drm: virtio_gpu: add support for ARGB8888 primary plane

[platform/kernel/linux-rpi.git] / kernel / sched / core.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  kernel/sched/core.c
 *
 *  Core kernel scheduler code and related syscalls
 *
 *  Copyright (C) 1991-2002  Linus Torvalds
 */
#define CREATE_TRACE_POINTS
#include <trace/events/sched.h>
#undef CREATE_TRACE_POINTS

#include "sched.h"

#include <linux/nospec.h>

#include <linux/kcov.h>
#include <linux/scs.h>

#include <asm/switch_to.h>
#include <asm/tlb.h>

#include "../workqueue_internal.h"
#include "../../io_uring/io-wq.h"
#include "../smpboot.h"

#include "pelt.h"
#include "smp.h"

/*
 * Export tracepoints that act as a bare tracehook (ie: have no trace event
 * associated with them) to allow external modules to probe them.
 */
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_cfs_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_rt_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_dl_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_irq_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_se_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_thermal_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_cpu_capacity_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_cfs_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);

DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);

#ifdef CONFIG_SCHED_DEBUG
/*
 * Debugging: various feature bits
 *
 * If SCHED_DEBUG is disabled, each compilation unit has its own copy of
 * sysctl_sched_features, defined in sched.h, to allow constants propagation
 * at compile time and compiler optimization based on features default.
 */
#define SCHED_FEAT(name, enabled)       \
        (1UL << __SCHED_FEAT_##name) * enabled |
const_debug unsigned int sysctl_sched_features =
#include "features.h"
        0;
#undef SCHED_FEAT

/*
 * Print a warning if need_resched is set for the given duration (if
 * LATENCY_WARN is enabled).
 *
 * If sysctl_resched_latency_warn_once is set, only one warning will be shown
 * per boot.
 */
__read_mostly int sysctl_resched_latency_warn_ms = 100;
__read_mostly int sysctl_resched_latency_warn_once = 1;
#endif /* CONFIG_SCHED_DEBUG */

/*
 * Number of tasks to iterate in a single balance run.
 * Limited because this is done with IRQs disabled.
 */
#ifdef CONFIG_PREEMPT_RT
const_debug unsigned int sysctl_sched_nr_migrate = 8;
#else
const_debug unsigned int sysctl_sched_nr_migrate = 32;
#endif

/*
 * period over which we measure -rt task CPU usage in us.
 * default: 1s
 */
unsigned int sysctl_sched_rt_period = 1000000;

__read_mostly int scheduler_running;

#ifdef CONFIG_SCHED_CORE

DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);

/* kernel prio, less is more */
static inline int __task_prio(struct task_struct *p)
{
        if (p->sched_class == &stop_sched_class) /* trumps deadline */
                return -2;

        if (rt_prio(p->prio)) /* includes deadline */
                return p->prio; /* [-1, 99] */

        if (p->sched_class == &idle_sched_class)
                return MAX_RT_PRIO + NICE_WIDTH; /* 140 */

        return MAX_RT_PRIO + MAX_NICE; /* 120, squash fair */
}

/*
 * l(a,b)
 * le(a,b) := !l(b,a)
 * g(a,b)  := l(b,a)
 * ge(a,b) := !l(a,b)
 */

/* real prio, less is less */
static inline bool prio_less(struct task_struct *a, struct task_struct *b, bool in_fi)
{

        int pa = __task_prio(a), pb = __task_prio(b);

        if (-pa < -pb)
                return true;

        if (-pb < -pa)
                return false;

        if (pa == -1) /* dl_prio() doesn't work because of stop_class above */
                return !dl_time_before(a->dl.deadline, b->dl.deadline);

        if (pa == MAX_RT_PRIO + MAX_NICE)       /* fair */
                return cfs_prio_less(a, b, in_fi);

        return false;
}

static inline bool __sched_core_less(struct task_struct *a, struct task_struct *b)
{
        if (a->core_cookie < b->core_cookie)
                return true;

        if (a->core_cookie > b->core_cookie)
                return false;

        /* flip prio, so high prio is leftmost */
        if (prio_less(b, a, task_rq(a)->core->core_forceidle))
                return true;

        return false;
}

#define __node_2_sc(node) rb_entry((node), struct task_struct, core_node)

static inline bool rb_sched_core_less(struct rb_node *a, const struct rb_node *b)
{
        return __sched_core_less(__node_2_sc(a), __node_2_sc(b));
}

static inline int rb_sched_core_cmp(const void *key, const struct rb_node *node)
{
        const struct task_struct *p = __node_2_sc(node);
        unsigned long cookie = (unsigned long)key;

        if (cookie < p->core_cookie)
                return -1;

        if (cookie > p->core_cookie)
                return 1;

        return 0;
}

void sched_core_enqueue(struct rq *rq, struct task_struct *p)
{
        rq->core->core_task_seq++;

        if (!p->core_cookie)
                return;

        rb_add(&p->core_node, &rq->core_tree, rb_sched_core_less);
}

void sched_core_dequeue(struct rq *rq, struct task_struct *p)
{
        rq->core->core_task_seq++;

        if (!sched_core_enqueued(p))
                return;

        rb_erase(&p->core_node, &rq->core_tree);
        RB_CLEAR_NODE(&p->core_node);
}

/*
 * Find left-most (aka, highest priority) task matching @cookie.
 */
static struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie)
{
        struct rb_node *node;

        node = rb_find_first((void *)cookie, &rq->core_tree, rb_sched_core_cmp);
        /*
         * The idle task always matches any cookie!
         */
        if (!node)
                return idle_sched_class.pick_task(rq);

        return __node_2_sc(node);
}

static struct task_struct *sched_core_next(struct task_struct *p, unsigned long cookie)
{
        struct rb_node *node = &p->core_node;

        node = rb_next(node);
        if (!node)
                return NULL;

        p = container_of(node, struct task_struct, core_node);
        if (p->core_cookie != cookie)
                return NULL;

        return p;
}

/*
 * Magic required such that:
 *
 *      raw_spin_rq_lock(rq);
 *      ...
 *      raw_spin_rq_unlock(rq);
 *
 * ends up locking and unlocking the _same_ lock, and all CPUs
 * always agree on what rq has what lock.
 *
 * XXX entirely possible to selectively enable cores, don't bother for now.
 */

static DEFINE_MUTEX(sched_core_mutex);
static atomic_t sched_core_count;
static struct cpumask sched_core_mask;

static void sched_core_lock(int cpu, unsigned long *flags)
{
        const struct cpumask *smt_mask = cpu_smt_mask(cpu);
        int t, i = 0;

        local_irq_save(*flags);
        for_each_cpu(t, smt_mask)
                raw_spin_lock_nested(&cpu_rq(t)->__lock, i++);
}

static void sched_core_unlock(int cpu, unsigned long *flags)
{
        const struct cpumask *smt_mask = cpu_smt_mask(cpu);
        int t;

        for_each_cpu(t, smt_mask)
                raw_spin_unlock(&cpu_rq(t)->__lock);
        local_irq_restore(*flags);
}

static void __sched_core_flip(bool enabled)
{
        unsigned long flags;
        int cpu, t;

        cpus_read_lock();

        /*
         * Toggle the online cores, one by one.
         */
        cpumask_copy(&sched_core_mask, cpu_online_mask);
        for_each_cpu(cpu, &sched_core_mask) {
                const struct cpumask *smt_mask = cpu_smt_mask(cpu);

                sched_core_lock(cpu, &flags);

                for_each_cpu(t, smt_mask)
                        cpu_rq(t)->core_enabled = enabled;

                sched_core_unlock(cpu, &flags);

                cpumask_andnot(&sched_core_mask, &sched_core_mask, smt_mask);
        }

        /*
         * Toggle the offline CPUs.
         */
        cpumask_copy(&sched_core_mask, cpu_possible_mask);
        cpumask_andnot(&sched_core_mask, &sched_core_mask, cpu_online_mask);

        for_each_cpu(cpu, &sched_core_mask)
                cpu_rq(cpu)->core_enabled = enabled;

        cpus_read_unlock();
}

static void sched_core_assert_empty(void)
{
        int cpu;

        for_each_possible_cpu(cpu)
                WARN_ON_ONCE(!RB_EMPTY_ROOT(&cpu_rq(cpu)->core_tree));
}

static void __sched_core_enable(void)
{
        static_branch_enable(&__sched_core_enabled);
        /*
         * Ensure all previous instances of raw_spin_rq_*lock() have finished
         * and future ones will observe !sched_core_disabled().
         */
        synchronize_rcu();
        __sched_core_flip(true);
        sched_core_assert_empty();
}

static void __sched_core_disable(void)
{
        sched_core_assert_empty();
        __sched_core_flip(false);
        static_branch_disable(&__sched_core_enabled);
}

void sched_core_get(void)
{
        if (atomic_inc_not_zero(&sched_core_count))
                return;

        mutex_lock(&sched_core_mutex);
        if (!atomic_read(&sched_core_count))
                __sched_core_enable();

        smp_mb__before_atomic();
        atomic_inc(&sched_core_count);
        mutex_unlock(&sched_core_mutex);
}

static void __sched_core_put(struct work_struct *work)
{
        if (atomic_dec_and_mutex_lock(&sched_core_count, &sched_core_mutex)) {
                __sched_core_disable();
                mutex_unlock(&sched_core_mutex);
        }
}

void sched_core_put(void)
{
        static DECLARE_WORK(_work, __sched_core_put);

        /*
         * "There can be only one"
         *
         * Either this is the last one, or we don't actually need to do any
         * 'work'. If it is the last *again*, we rely on
         * WORK_STRUCT_PENDING_BIT.
         */
        if (!atomic_add_unless(&sched_core_count, -1, 1))
                schedule_work(&_work);
}

#else /* !CONFIG_SCHED_CORE */

static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }

#endif /* CONFIG_SCHED_CORE */

/*
 * part of the period that we allow rt tasks to run in us.
 * default: 0.95s
 */
int sysctl_sched_rt_runtime = 950000;


/*
 * Serialization rules:
 *
 * Lock order:
 *
 *   p->pi_lock
 *     rq->lock
 *       hrtimer_cpu_base->lock (hrtimer_start() for bandwidth controls)
 *
 *  rq1->lock
 *    rq2->lock  where: rq1 < rq2
 *
 * Regular state:
 *
 * Normal scheduling state is serialized by rq->lock. __schedule() takes the
 * local CPU's rq->lock, it optionally removes the task from the runqueue and
 * always looks at the local rq data structures to find the most eligible task
 * to run next.
 *
 * Task enqueue is also under rq->lock, possibly taken from another CPU.
 * Wakeups from another LLC domain might use an IPI to transfer the enqueue to
 * the local CPU to avoid bouncing the runqueue state around [ see
 * ttwu_queue_wakelist() ]
 *
 * Task wakeup, specifically wakeups that involve migration, are horribly
 * complicated to avoid having to take two rq->locks.
 *
 * Special state:
 *
 * System-calls and anything external will use task_rq_lock() which acquires
 * both p->pi_lock and rq->lock. As a consequence the state they change is
 * stable while holding either lock:
 *
 *  - sched_setaffinity()/
 *    set_cpus_allowed_ptr():   p->cpus_ptr, p->nr_cpus_allowed
 *  - set_user_nice():          p->se.load, p->*prio
 *  - __sched_setscheduler():   p->sched_class, p->policy, p->*prio,
 *                              p->se.load, p->rt_priority,
 *                              p->dl.dl_{runtime, deadline, period, flags, bw, density}
 *  - sched_setnuma():          p->numa_preferred_nid
 *  - sched_move_task()/
 *    cpu_cgroup_fork():        p->sched_task_group
 *  - uclamp_update_active()    p->uclamp*
 *
 * p->state <- TASK_*:
 *
 *   is changed locklessly using set_current_state(), __set_current_state() or
 *   set_special_state(), see their respective comments, or by
 *   try_to_wake_up(). This latter uses p->pi_lock to serialize against
 *   concurrent self.
 *
 * p->on_rq <- { 0, 1 = TASK_ON_RQ_QUEUED, 2 = TASK_ON_RQ_MIGRATING }:
 *
 *   is set by activate_task() and cleared by deactivate_task(), under
 *   rq->lock. Non-zero indicates the task is runnable, the special
 *   ON_RQ_MIGRATING state is used for migration without holding both
 *   rq->locks. It indicates task_cpu() is not stable, see task_rq_lock().
 *
 * p->on_cpu <- { 0, 1 }:
 *
 *   is set by prepare_task() and cleared by finish_task() such that it will be
 *   set before p is scheduled-in and cleared after p is scheduled-out, both
 *   under rq->lock. Non-zero indicates the task is running on its CPU.
 *
 *   [ The astute reader will observe that it is possible for two tasks on one
 *     CPU to have ->on_cpu = 1 at the same time. ]
 *
 * task_cpu(p): is changed by set_task_cpu(), the rules are:
 *
 *  - Don't call set_task_cpu() on a blocked task:
 *
 *    We don't care what CPU we're not running on, this simplifies hotplug,
 *    the CPU assignment of blocked tasks isn't required to be valid.
 *
 *  - for try_to_wake_up(), called under p->pi_lock:
 *
 *    This allows try_to_wake_up() to only take one rq->lock, see its comment.
 *
 *  - for migration called under rq->lock:
 *    [ see task_on_rq_migrating() in task_rq_lock() ]
 *
 *    o move_queued_task()
 *    o detach_task()
 *
 *  - for migration called under double_rq_lock():
 *
 *    o __migrate_swap_task()
 *    o push_rt_task() / pull_rt_task()
 *    o push_dl_task() / pull_dl_task()
 *    o dl_task_offline_migration()
 *
 */

void raw_spin_rq_lock_nested(struct rq *rq, int subclass)
{
        raw_spinlock_t *lock;

        /* Matches synchronize_rcu() in __sched_core_enable() */
        preempt_disable();
        if (sched_core_disabled()) {
                raw_spin_lock_nested(&rq->__lock, subclass);
                /* preempt_count *MUST* be > 1 */
                preempt_enable_no_resched();
                return;
        }

        for (;;) {
                lock = __rq_lockp(rq);
                raw_spin_lock_nested(lock, subclass);
                if (likely(lock == __rq_lockp(rq))) {
                        /* preempt_count *MUST* be > 1 */
                        preempt_enable_no_resched();
                        return;
                }
                raw_spin_unlock(lock);
        }
}

bool raw_spin_rq_trylock(struct rq *rq)
{
        raw_spinlock_t *lock;
        bool ret;

        /* Matches synchronize_rcu() in __sched_core_enable() */
        preempt_disable();
        if (sched_core_disabled()) {
                ret = raw_spin_trylock(&rq->__lock);
                preempt_enable();
                return ret;
        }

        for (;;) {
                lock = __rq_lockp(rq);
                ret = raw_spin_trylock(lock);
                if (!ret || (likely(lock == __rq_lockp(rq)))) {
                        preempt_enable();
                        return ret;
                }
                raw_spin_unlock(lock);
        }
}

void raw_spin_rq_unlock(struct rq *rq)
{
        raw_spin_unlock(rq_lockp(rq));
}

#ifdef CONFIG_SMP
/*
 * double_rq_lock - safely lock two runqueues
 */
void double_rq_lock(struct rq *rq1, struct rq *rq2)
{
        lockdep_assert_irqs_disabled();

        if (rq_order_less(rq2, rq1))
                swap(rq1, rq2);

        raw_spin_rq_lock(rq1);
        if (__rq_lockp(rq1) != __rq_lockp(rq2))
                raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);

        double_rq_clock_clear_update(rq1, rq2);
}
#endif

/*
 * __task_rq_lock - lock the rq @p resides on.
 */
struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
        __acquires(rq->lock)
{
        struct rq *rq;

        lockdep_assert_held(&p->pi_lock);

        for (;;) {
                rq = task_rq(p);
                raw_spin_rq_lock(rq);
                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
                        rq_pin_lock(rq, rf);
                        return rq;
                }
                raw_spin_rq_unlock(rq);

                while (unlikely(task_on_rq_migrating(p)))
                        cpu_relax();
        }
}

/*
 * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
 */
struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
        __acquires(p->pi_lock)
        __acquires(rq->lock)
{
        struct rq *rq;

        for (;;) {
                raw_spin_lock_irqsave(&p->pi_lock, rf->flags);
                rq = task_rq(p);
                raw_spin_rq_lock(rq);
                /*
                 *      move_queued_task()              task_rq_lock()
                 *
                 *      ACQUIRE (rq->lock)
                 *      [S] ->on_rq = MIGRATING         [L] rq = task_rq()
                 *      WMB (__set_task_cpu())          ACQUIRE (rq->lock);
                 *      [S] ->cpu = new_cpu             [L] task_rq()
                 *                                      [L] ->on_rq
                 *      RELEASE (rq->lock)
                 *
                 * If we observe the old CPU in task_rq_lock(), the acquire of
                 * the old rq->lock will fully serialize against the stores.
                 *
                 * If we observe the new CPU in task_rq_lock(), the address
                 * dependency headed by '[L] rq = task_rq()' and the acquire
                 * will pair with the WMB to ensure we then also see migrating.
                 */
                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
                        rq_pin_lock(rq, rf);
                        return rq;
                }
                raw_spin_rq_unlock(rq);
                raw_spin_unlock_irqrestore(&p->pi_lock, rf->flags);

                while (unlikely(task_on_rq_migrating(p)))
                        cpu_relax();
        }
}

/*
 * RQ-clock updating methods:
 */

static void update_rq_clock_task(struct rq *rq, s64 delta)
{
/*
 * In theory, the compile should just see 0 here, and optimize out the call
 * to sched_rt_avg_update. But I don't trust it...
 */
        s64 __maybe_unused steal = 0, irq_delta = 0;

#ifdef CONFIG_IRQ_TIME_ACCOUNTING
        irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;

        /*
         * Since irq_time is only updated on {soft,}irq_exit, we might run into
         * this case when a previous update_rq_clock() happened inside a
         * {soft,}irq region.
         *
         * When this happens, we stop ->clock_task and only update the
         * prev_irq_time stamp to account for the part that fit, so that a next
         * update will consume the rest. This ensures ->clock_task is
         * monotonic.
         *
         * It does however cause some slight miss-attribution of {soft,}irq
         * time, a more accurate solution would be to update the irq_time using
         * the current rq->clock timestamp, except that would require using
         * atomic ops.
         */
        if (irq_delta > delta)
                irq_delta = delta;

        rq->prev_irq_time += irq_delta;
        delta -= irq_delta;
#endif
#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
        if (static_key_false((&paravirt_steal_rq_enabled))) {
                steal = paravirt_steal_clock(cpu_of(rq));
                steal -= rq->prev_steal_time_rq;

                if (unlikely(steal > delta))
                        steal = delta;

                rq->prev_steal_time_rq += steal;
                delta -= steal;
        }
#endif

        rq->clock_task += delta;

#ifdef CONFIG_HAVE_SCHED_AVG_IRQ
        if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
                update_irq_load_avg(rq, irq_delta + steal);
#endif
        update_rq_clock_pelt(rq, delta);
}

void update_rq_clock(struct rq *rq)
{
        s64 delta;

        lockdep_assert_rq_held(rq);

        if (rq->clock_update_flags & RQCF_ACT_SKIP)
                return;

#ifdef CONFIG_SCHED_DEBUG
        if (sched_feat(WARN_DOUBLE_CLOCK))
                SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
        rq->clock_update_flags |= RQCF_UPDATED;
#endif

        delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
        if (delta < 0)
                return;
        rq->clock += delta;
        update_rq_clock_task(rq, delta);
}

#ifdef CONFIG_SCHED_HRTICK
/*
 * Use HR-timers to deliver accurate preemption points.
 */

static void hrtick_clear(struct rq *rq)
{
        if (hrtimer_active(&rq->hrtick_timer))
                hrtimer_cancel(&rq->hrtick_timer);
}

/*
 * High-resolution timer tick.
 * Runs from hardirq context with interrupts disabled.
 */
static enum hrtimer_restart hrtick(struct hrtimer *timer)
{
        struct rq *rq = container_of(timer, struct rq, hrtick_timer);
        struct rq_flags rf;

        WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());

        rq_lock(rq, &rf);
        update_rq_clock(rq);
        rq->curr->sched_class->task_tick(rq, rq->curr, 1);
        rq_unlock(rq, &rf);

        return HRTIMER_NORESTART;
}

#ifdef CONFIG_SMP

static void __hrtick_restart(struct rq *rq)
{
        struct hrtimer *timer = &rq->hrtick_timer;
        ktime_t time = rq->hrtick_time;

        hrtimer_start(timer, time, HRTIMER_MODE_ABS_PINNED_HARD);
}

/*
 * called from hardirq (IPI) context
 */
static void __hrtick_start(void *arg)
{
        struct rq *rq = arg;
        struct rq_flags rf;

        rq_lock(rq, &rf);
        __hrtick_restart(rq);
        rq_unlock(rq, &rf);
}

/*
 * Called to set the hrtick timer state.
 *
 * called with rq->lock held and irqs disabled
 */
void hrtick_start(struct rq *rq, u64 delay)
{
        struct hrtimer *timer = &rq->hrtick_timer;
        s64 delta;

        /*
         * Don't schedule slices shorter than 10000ns, that just
         * doesn't make sense and can cause timer DoS.
         */
        delta = max_t(s64, delay, 10000LL);
        rq->hrtick_time = ktime_add_ns(timer->base->get_time(), delta);

        if (rq == this_rq())
                __hrtick_restart(rq);
        else
                smp_call_function_single_async(cpu_of(rq), &rq->hrtick_csd);
}

#else
/*
 * Called to set the hrtick timer state.
 *
 * called with rq->lock held and irqs disabled
 */
void hrtick_start(struct rq *rq, u64 delay)
{
        /*
         * Don't schedule slices shorter than 10000ns, that just
         * doesn't make sense. Rely on vruntime for fairness.
         */
        delay = max_t(u64, delay, 10000LL);
        hrtimer_start(&rq->hrtick_timer, ns_to_ktime(delay),
                      HRTIMER_MODE_REL_PINNED_HARD);
}

#endif /* CONFIG_SMP */

static void hrtick_rq_init(struct rq *rq)
{
#ifdef CONFIG_SMP
        INIT_CSD(&rq->hrtick_csd, __hrtick_start, rq);
#endif
        hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
        rq->hrtick_timer.function = hrtick;
}
#else   /* CONFIG_SCHED_HRTICK */
static inline void hrtick_clear(struct rq *rq)
{
}

static inline void hrtick_rq_init(struct rq *rq)
{
}
#endif  /* CONFIG_SCHED_HRTICK */

/*
 * cmpxchg based fetch_or, macro so it works for different integer types
 */
#define fetch_or(ptr, mask)                                             \
        ({                                                              \
                typeof(ptr) _ptr = (ptr);                               \
                typeof(mask) _mask = (mask);                            \
                typeof(*_ptr) _old, _val = *_ptr;                       \
                                                                        \
                for (;;) {                                              \
                        _old = cmpxchg(_ptr, _val, _val | _mask);       \
                        if (_old == _val)                               \
                                break;                                  \
                        _val = _old;                                    \
                }                                                       \
        _old;                                                           \
})

#if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
/*
 * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
 * this avoids any races wrt polling state changes and thereby avoids
 * spurious IPIs.
 */
static bool set_nr_and_not_polling(struct task_struct *p)
{
        struct thread_info *ti = task_thread_info(p);
        return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
}

/*
 * Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set.
 *
 * If this returns true, then the idle task promises to call
 * sched_ttwu_pending() and reschedule soon.
 */
static bool set_nr_if_polling(struct task_struct *p)
{
        struct thread_info *ti = task_thread_info(p);
        typeof(ti->flags) old, val = READ_ONCE(ti->flags);

        for (;;) {
                if (!(val & _TIF_POLLING_NRFLAG))
                        return false;
                if (val & _TIF_NEED_RESCHED)
                        return true;
                old = cmpxchg(&ti->flags, val, val | _TIF_NEED_RESCHED);
                if (old == val)
                        break;
                val = old;
        }
        return true;
}

#else
static bool set_nr_and_not_polling(struct task_struct *p)
{
        set_tsk_need_resched(p);
        return true;
}

#ifdef CONFIG_SMP
static bool set_nr_if_polling(struct task_struct *p)
{
        return false;
}
#endif
#endif

static bool __wake_q_add(struct wake_q_head *head, struct task_struct *task)
{
        struct wake_q_node *node = &task->wake_q;

        /*
         * Atomically grab the task, if ->wake_q is !nil already it means
         * it's already queued (either by us or someone else) and will get the
         * wakeup due to that.
         *
         * In order to ensure that a pending wakeup will observe our pending
         * state, even in the failed case, an explicit smp_mb() must be used.
         */
        smp_mb__before_atomic();
        if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)))
                return false;

        /*
         * The head is context local, there can be no concurrency.
         */
        *head->lastp = node;
        head->lastp = &node->next;
        return true;
}

/**
 * wake_q_add() - queue a wakeup for 'later' waking.
 * @head: the wake_q_head to add @task to
 * @task: the task to queue for 'later' wakeup
 *
 * Queue a task for later wakeup, most likely by the wake_up_q() call in the
 * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
 * instantly.
 *
 * This function must be used as-if it were wake_up_process(); IOW the task
 * must be ready to be woken at this location.
 */
void wake_q_add(struct wake_q_head *head, struct task_struct *task)
{
        if (__wake_q_add(head, task))
                get_task_struct(task);
}

/**
 * wake_q_add_safe() - safely queue a wakeup for 'later' waking.
 * @head: the wake_q_head to add @task to
 * @task: the task to queue for 'later' wakeup
 *
 * Queue a task for later wakeup, most likely by the wake_up_q() call in the
 * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
 * instantly.
 *
 * This function must be used as-if it were wake_up_process(); IOW the task
 * must be ready to be woken at this location.
 *
 * This function is essentially a task-safe equivalent to wake_q_add(). Callers
 * that already hold reference to @task can call the 'safe' version and trust
 * wake_q to do the right thing depending whether or not the @task is already
 * queued for wakeup.
 */
void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task)
{
        if (!__wake_q_add(head, task))
                put_task_struct(task);
}

void wake_up_q(struct wake_q_head *head)
{
        struct wake_q_node *node = head->first;

        while (node != WAKE_Q_TAIL) {
                struct task_struct *task;

                task = container_of(node, struct task_struct, wake_q);
                /* Task can safely be re-inserted now: */
                node = node->next;
                task->wake_q.next = NULL;

                /*
                 * wake_up_process() executes a full barrier, which pairs with
                 * the queueing in wake_q_add() so as not to miss wakeups.
                 */
                wake_up_process(task);
                put_task_struct(task);
        }
}

/*
 * resched_curr - mark rq's current task 'to be rescheduled now'.
 *
 * On UP this means the setting of the need_resched flag, on SMP it
 * might also involve a cross-CPU call to trigger the scheduler on
 * the target CPU.
 */
void resched_curr(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        int cpu;

        lockdep_assert_rq_held(rq);

        if (test_tsk_need_resched(curr))
                return;

        cpu = cpu_of(rq);

        if (cpu == smp_processor_id()) {
                set_tsk_need_resched(curr);
                set_preempt_need_resched();
                return;
        }

        if (set_nr_and_not_polling(curr))
                smp_send_reschedule(cpu);
        else
                trace_sched_wake_idle_without_ipi(cpu);
}

#ifdef CONFIG_PREEMPT_LAZY

static int tsk_is_polling(struct task_struct *p)
{
#ifdef TIF_POLLING_NRFLAG
        return test_tsk_thread_flag(p, TIF_POLLING_NRFLAG);
#else
        return 0;
#endif
}

void resched_curr_lazy(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        int cpu;

        if (!sched_feat(PREEMPT_LAZY)) {
                resched_curr(rq);
                return;
        }

        if (test_tsk_need_resched(curr))
                return;

        if (test_tsk_need_resched_lazy(curr))
                return;

        set_tsk_need_resched_lazy(curr);

        cpu = cpu_of(rq);
        if (cpu == smp_processor_id())
                return;

        /* NEED_RESCHED_LAZY must be visible before we test polling */
        smp_mb();
        if (!tsk_is_polling(curr))
                smp_send_reschedule(cpu);
}
#endif

void resched_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long flags;

        raw_spin_rq_lock_irqsave(rq, flags);
        if (cpu_online(cpu) || cpu == smp_processor_id())
                resched_curr(rq);
        raw_spin_rq_unlock_irqrestore(rq, flags);
}

#ifdef CONFIG_SMP
#ifdef CONFIG_NO_HZ_COMMON
/*
 * In the semi idle case, use the nearest busy CPU for migrating timers
 * from an idle CPU.  This is good for power-savings.
 *
 * We don't do similar optimization for completely idle system, as
 * selecting an idle CPU will add more delays to the timers than intended
 * (as that CPU's timer base may not be uptodate wrt jiffies etc).
 */
int get_nohz_timer_target(void)
{
        int i, cpu = smp_processor_id(), default_cpu = -1;
        struct sched_domain *sd;
        const struct cpumask *hk_mask;

        if (housekeeping_cpu(cpu, HK_FLAG_TIMER)) {
                if (!idle_cpu(cpu))
                        return cpu;
                default_cpu = cpu;
        }

        hk_mask = housekeeping_cpumask(HK_FLAG_TIMER);

        rcu_read_lock();
        for_each_domain(cpu, sd) {
                for_each_cpu_and(i, sched_domain_span(sd), hk_mask) {
                        if (cpu == i)
                                continue;

                        if (!idle_cpu(i)) {
                                cpu = i;
                                goto unlock;
                        }
                }
        }

        if (default_cpu == -1)
                default_cpu = housekeeping_any_cpu(HK_FLAG_TIMER);
        cpu = default_cpu;
unlock:
        rcu_read_unlock();
        return cpu;
}

/*
 * When add_timer_on() enqueues a timer into the timer wheel of an
 * idle CPU then this timer might expire before the next timer event
 * which is scheduled to wake up that CPU. In case of a completely
 * idle system the next event might even be infinite time into the
 * future. wake_up_idle_cpu() ensures that the CPU is woken up and
 * leaves the inner idle loop so the newly added timer is taken into
 * account when the CPU goes back to idle and evaluates the timer
 * wheel for the next timer event.
 */
static void wake_up_idle_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (cpu == smp_processor_id())
                return;

        if (set_nr_and_not_polling(rq->idle))
                smp_send_reschedule(cpu);
        else
                trace_sched_wake_idle_without_ipi(cpu);
}

static bool wake_up_full_nohz_cpu(int cpu)
{
        /*
         * We just need the target to call irq_exit() and re-evaluate
         * the next tick. The nohz full kick at least implies that.
         * If needed we can still optimize that later with an
         * empty IRQ.
         */
        if (cpu_is_offline(cpu))
                return true;  /* Don't try to wake offline CPUs. */
        if (tick_nohz_full_cpu(cpu)) {
                if (cpu != smp_processor_id() ||
                    tick_nohz_tick_stopped())
                        tick_nohz_full_kick_cpu(cpu);
                return true;
        }

        return false;
}

/*
 * Wake up the specified CPU.  If the CPU is going offline, it is the
 * caller's responsibility to deal with the lost wakeup, for example,
 * by hooking into the CPU_DEAD notifier like timers and hrtimers do.
 */
void wake_up_nohz_cpu(int cpu)
{
        if (!wake_up_full_nohz_cpu(cpu))
                wake_up_idle_cpu(cpu);
}

static void nohz_csd_func(void *info)
{
        struct rq *rq = info;
        int cpu = cpu_of(rq);
        unsigned int flags;

        /*
         * Release the rq::nohz_csd.
         */
        flags = atomic_fetch_andnot(NOHZ_KICK_MASK | NOHZ_NEWILB_KICK, nohz_flags(cpu));
        WARN_ON(!(flags & NOHZ_KICK_MASK));

        rq->idle_balance = idle_cpu(cpu);
        if (rq->idle_balance && !need_resched()) {
                rq->nohz_idle_balance = flags;
                raise_softirq_irqoff(SCHED_SOFTIRQ);
        }
}

#endif /* CONFIG_NO_HZ_COMMON */

#ifdef CONFIG_NO_HZ_FULL
bool sched_can_stop_tick(struct rq *rq)
{
        int fifo_nr_running;

        /* Deadline tasks, even if single, need the tick */
        if (rq->dl.dl_nr_running)
                return false;

        /*
         * If there are more than one RR tasks, we need the tick to affect the
         * actual RR behaviour.
         */
        if (rq->rt.rr_nr_running) {
                if (rq->rt.rr_nr_running == 1)
                        return true;
                else
                        return false;
        }

        /*
         * If there's no RR tasks, but FIFO tasks, we can skip the tick, no
         * forced preemption between FIFO tasks.
         */
        fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
        if (fifo_nr_running)
                return true;

        /*
         * If there are no DL,RR/FIFO tasks, there must only be CFS tasks left;
         * if there's more than one we need the tick for involuntary
         * preemption.
         */
        if (rq->nr_running > 1)
                return false;

        return true;
}
#endif /* CONFIG_NO_HZ_FULL */
#endif /* CONFIG_SMP */

#if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \
                        (defined(CONFIG_SMP) || defined(CONFIG_CFS_BANDWIDTH)))
/*
 * Iterate task_group tree rooted at *from, calling @down when first entering a
 * node and @up when leaving it for the final time.
 *
 * Caller must hold rcu_lock or sufficient equivalent.
 */
int walk_tg_tree_from(struct task_group *from,
                             tg_visitor down, tg_visitor up, void *data)
{
        struct task_group *parent, *child;
        int ret;

        parent = from;

down:
        ret = (*down)(parent, data);
        if (ret)
                goto out;
        list_for_each_entry_rcu(child, &parent->children, siblings) {
                parent = child;
                goto down;

up:
                continue;
        }
        ret = (*up)(parent, data);
        if (ret || parent == from)
                goto out;

        child = parent;
        parent = parent->parent;
        if (parent)
                goto up;
out:
        return ret;
}

int tg_nop(struct task_group *tg, void *data)
{
        return 0;
}
#endif

static void set_load_weight(struct task_struct *p, bool update_load)
{
        int prio = p->static_prio - MAX_RT_PRIO;
        struct load_weight *load = &p->se.load;

        /*
         * SCHED_IDLE tasks get minimal weight:
         */
        if (task_has_idle_policy(p)) {
                load->weight = scale_load(WEIGHT_IDLEPRIO);
                load->inv_weight = WMULT_IDLEPRIO;
                return;
        }

        /*
         * SCHED_OTHER tasks have to update their load when changing their
         * weight
         */
        if (update_load && p->sched_class == &fair_sched_class) {
                reweight_task(p, prio);
        } else {
                load->weight = scale_load(sched_prio_to_weight[prio]);
                load->inv_weight = sched_prio_to_wmult[prio];
        }
}

#ifdef CONFIG_UCLAMP_TASK
/*
 * Serializes updates of utilization clamp values
 *
 * The (slow-path) user-space triggers utilization clamp value updates which
 * can require updates on (fast-path) scheduler's data structures used to
 * support enqueue/dequeue operations.
 * While the per-CPU rq lock protects fast-path update operations, user-space
 * requests are serialized using a mutex to reduce the risk of conflicting
 * updates or API abuses.
 */
static DEFINE_MUTEX(uclamp_mutex);

/* Max allowed minimum utilization */
unsigned int sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;

/* Max allowed maximum utilization */
unsigned int sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;

/*
 * By default RT tasks run at the maximum performance point/capacity of the
 * system. Uclamp enforces this by always setting UCLAMP_MIN of RT tasks to
 * SCHED_CAPACITY_SCALE.
 *
 * This knob allows admins to change the default behavior when uclamp is being
 * used. In battery powered devices, particularly, running at the maximum
 * capacity and frequency will increase energy consumption and shorten the
 * battery life.
 *
 * This knob only affects RT tasks that their uclamp_se->user_defined == false.
 *
 * This knob will not override the system default sched_util_clamp_min defined
 * above.
 */
unsigned int sysctl_sched_uclamp_util_min_rt_default = SCHED_CAPACITY_SCALE;

/* All clamps are required to be less or equal than these values */
static struct uclamp_se uclamp_default[UCLAMP_CNT];

/*
 * This static key is used to reduce the uclamp overhead in the fast path. It
 * primarily disables the call to uclamp_rq_{inc, dec}() in
 * enqueue/dequeue_task().
 *
 * This allows users to continue to enable uclamp in their kernel config with
 * minimum uclamp overhead in the fast path.
 *
 * As soon as userspace modifies any of the uclamp knobs, the static key is
 * enabled, since we have an actual users that make use of uclamp
 * functionality.
 *
 * The knobs that would enable this static key are:
 *
 *   * A task modifying its uclamp value with sched_setattr().
 *   * An admin modifying the sysctl_sched_uclamp_{min, max} via procfs.
 *   * An admin modifying the cgroup cpu.uclamp.{min, max}
 */
DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);

/* Integer rounded range for each bucket */
#define UCLAMP_BUCKET_DELTA DIV_ROUND_CLOSEST(SCHED_CAPACITY_SCALE, UCLAMP_BUCKETS)

#define for_each_clamp_id(clamp_id) \
        for ((clamp_id) = 0; (clamp_id) < UCLAMP_CNT; (clamp_id)++)

static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
{
        return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
}

static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
{
        if (clamp_id == UCLAMP_MIN)
                return 0;
        return SCHED_CAPACITY_SCALE;
}

static inline void uclamp_se_set(struct uclamp_se *uc_se,
                                 unsigned int value, bool user_defined)
{
        uc_se->value = value;
        uc_se->bucket_id = uclamp_bucket_id(value);
        uc_se->user_defined = user_defined;
}

static inline unsigned int
uclamp_idle_value(struct rq *rq, enum uclamp_id clamp_id,
                  unsigned int clamp_value)
{
        /*
         * Avoid blocked utilization pushing up the frequency when we go
         * idle (which drops the max-clamp) by retaining the last known
         * max-clamp.
         */
        if (clamp_id == UCLAMP_MAX) {
                rq->uclamp_flags |= UCLAMP_FLAG_IDLE;
                return clamp_value;
        }

        return uclamp_none(UCLAMP_MIN);
}

static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
                                     unsigned int clamp_value)
{
        /* Reset max-clamp retention only on idle exit */
        if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
                return;

        WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
}

static inline
unsigned int uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
                                   unsigned int clamp_value)
{
        struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
        int bucket_id = UCLAMP_BUCKETS - 1;

        /*
         * Since both min and max clamps are max aggregated, find the
         * top most bucket with tasks in.
         */
        for ( ; bucket_id >= 0; bucket_id--) {
                if (!bucket[bucket_id].tasks)
                        continue;
                return bucket[bucket_id].value;
        }

        /* No tasks -- default clamp values */
        return uclamp_idle_value(rq, clamp_id, clamp_value);
}

static void __uclamp_update_util_min_rt_default(struct task_struct *p)
{
        unsigned int default_util_min;
        struct uclamp_se *uc_se;

        lockdep_assert_held(&p->pi_lock);

        uc_se = &p->uclamp_req[UCLAMP_MIN];

        /* Only sync if user didn't override the default */
        if (uc_se->user_defined)
                return;

        default_util_min = sysctl_sched_uclamp_util_min_rt_default;
        uclamp_se_set(uc_se, default_util_min, false);
}

static void uclamp_update_util_min_rt_default(struct task_struct *p)
{
        struct rq_flags rf;
        struct rq *rq;

        if (!rt_task(p))
                return;

        /* Protect updates to p->uclamp_* */
        rq = task_rq_lock(p, &rf);
        __uclamp_update_util_min_rt_default(p);
        task_rq_unlock(rq, p, &rf);
}

static void uclamp_sync_util_min_rt_default(void)
{
        struct task_struct *g, *p;

        /*
         * copy_process()                       sysctl_uclamp
         *                                        uclamp_min_rt = X;
         *   write_lock(&tasklist_lock)           read_lock(&tasklist_lock)
         *   // link thread                       smp_mb__after_spinlock()
         *   write_unlock(&tasklist_lock)         read_unlock(&tasklist_lock);
         *   sched_post_fork()                    for_each_process_thread()
         *     __uclamp_sync_rt()                   __uclamp_sync_rt()
         *
         * Ensures that either sched_post_fork() will observe the new
         * uclamp_min_rt or for_each_process_thread() will observe the new
         * task.
         */
        read_lock(&tasklist_lock);
        smp_mb__after_spinlock();
        read_unlock(&tasklist_lock);

        rcu_read_lock();
        for_each_process_thread(g, p)
                uclamp_update_util_min_rt_default(p);
        rcu_read_unlock();
}

static inline struct uclamp_se
uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
{
        /* Copy by value as we could modify it */
        struct uclamp_se uc_req = p->uclamp_req[clamp_id];
#ifdef CONFIG_UCLAMP_TASK_GROUP
        unsigned int tg_min, tg_max, value;

        /*
         * Tasks in autogroups or root task group will be
         * restricted by system defaults.
         */
        if (task_group_is_autogroup(task_group(p)))
                return uc_req;
        if (task_group(p) == &root_task_group)
                return uc_req;

        tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
        tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
        value = uc_req.value;
        value = clamp(value, tg_min, tg_max);
        uclamp_se_set(&uc_req, value, false);
#endif

        return uc_req;
}

/*
 * The effective clamp bucket index of a task depends on, by increasing
 * priority:
 * - the task specific clamp value, when explicitly requested from userspace
 * - the task group effective clamp value, for tasks not either in the root
 *   group or in an autogroup
 * - the system default clamp value, defined by the sysadmin
 */
static inline struct uclamp_se
uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
{
        struct uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id);
        struct uclamp_se uc_max = uclamp_default[clamp_id];

        /* System default restrictions always apply */
        if (unlikely(uc_req.value > uc_max.value))
                return uc_max;

        return uc_req;
}

unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
{
        struct uclamp_se uc_eff;

        /* Task currently refcounted: use back-annotated (effective) value */
        if (p->uclamp[clamp_id].active)
                return (unsigned long)p->uclamp[clamp_id].value;

        uc_eff = uclamp_eff_get(p, clamp_id);

        return (unsigned long)uc_eff.value;
}

/*
 * When a task is enqueued on a rq, the clamp bucket currently defined by the
 * task's uclamp::bucket_id is refcounted on that rq. This also immediately
 * updates the rq's clamp value if required.
 *
 * Tasks can have a task-specific value requested from user-space, track
 * within each bucket the maximum value for tasks refcounted in it.
 * This "local max aggregation" allows to track the exact "requested" value
 * for each bucket when all its RUNNABLE tasks require the same clamp.
 */
static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
                                    enum uclamp_id clamp_id)
{
        struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
        struct uclamp_se *uc_se = &p->uclamp[clamp_id];
        struct uclamp_bucket *bucket;

        lockdep_assert_rq_held(rq);

        /* Update task effective clamp */
        p->uclamp[clamp_id] = uclamp_eff_get(p, clamp_id);

        bucket = &uc_rq->bucket[uc_se->bucket_id];
        bucket->tasks++;
        uc_se->active = true;

        uclamp_idle_reset(rq, clamp_id, uc_se->value);

        /*
         * Local max aggregation: rq buckets always track the max
         * "requested" clamp value of its RUNNABLE tasks.
         */
        if (bucket->tasks == 1 || uc_se->value > bucket->value)
                bucket->value = uc_se->value;

        if (uc_se->value > READ_ONCE(uc_rq->value))
                WRITE_ONCE(uc_rq->value, uc_se->value);
}

/*
 * When a task is dequeued from a rq, the clamp bucket refcounted by the task
 * is released. If this is the last task reference counting the rq's max
 * active clamp value, then the rq's clamp value is updated.
 *
 * Both refcounted tasks and rq's cached clamp values are expected to be
 * always valid. If it's detected they are not, as defensive programming,
 * enforce the expected state and warn.
 */
static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
                                    enum uclamp_id clamp_id)
{
        struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
        struct uclamp_se *uc_se = &p->uclamp[clamp_id];
        struct uclamp_bucket *bucket;
        unsigned int bkt_clamp;
        unsigned int rq_clamp;

        lockdep_assert_rq_held(rq);

        /*
         * If sched_uclamp_used was enabled after task @p was enqueued,
         * we could end up with unbalanced call to uclamp_rq_dec_id().
         *
         * In this case the uc_se->active flag should be false since no uclamp
         * accounting was performed at enqueue time and we can just return
         * here.
         *
         * Need to be careful of the following enqueue/dequeue ordering
         * problem too
         *
         *      enqueue(taskA)
         *      // sched_uclamp_used gets enabled
         *      enqueue(taskB)
         *      dequeue(taskA)
         *      // Must not decrement bucket->tasks here
         *      dequeue(taskB)
         *
         * where we could end up with stale data in uc_se and
         * bucket[uc_se->bucket_id].
         *
         * The following check here eliminates the possibility of such race.
         */
        if (unlikely(!uc_se->active))
                return;

        bucket = &uc_rq->bucket[uc_se->bucket_id];

        SCHED_WARN_ON(!bucket->tasks);
        if (likely(bucket->tasks))
                bucket->tasks--;

        uc_se->active = false;

        /*
         * Keep "local max aggregation" simple and accept to (possibly)
         * overboost some RUNNABLE tasks in the same bucket.
         * The rq clamp bucket value is reset to its base value whenever
         * there are no more RUNNABLE tasks refcounting it.
         */
        if (likely(bucket->tasks))
                return;

        rq_clamp = READ_ONCE(uc_rq->value);
        /*
         * Defensive programming: this should never happen. If it happens,
         * e.g. due to future modification, warn and fixup the expected value.
         */
        SCHED_WARN_ON(bucket->value > rq_clamp);
        if (bucket->value >= rq_clamp) {
                bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
                WRITE_ONCE(uc_rq->value, bkt_clamp);
        }
}

static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
{
        enum uclamp_id clamp_id;

        /*
         * Avoid any overhead until uclamp is actually used by the userspace.
         *
         * The condition is constructed such that a NOP is generated when
         * sched_uclamp_used is disabled.
         */
        if (!static_branch_unlikely(&sched_uclamp_used))
                return;

        if (unlikely(!p->sched_class->uclamp_enabled))
                return;

        for_each_clamp_id(clamp_id)
                uclamp_rq_inc_id(rq, p, clamp_id);

        /* Reset clamp idle holding when there is one RUNNABLE task */
        if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
                rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
}

static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
{
        enum uclamp_id clamp_id;

        /*
         * Avoid any overhead until uclamp is actually used by the userspace.
         *
         * The condition is constructed such that a NOP is generated when
         * sched_uclamp_used is disabled.
         */
        if (!static_branch_unlikely(&sched_uclamp_used))
                return;

        if (unlikely(!p->sched_class->uclamp_enabled))
                return;

        for_each_clamp_id(clamp_id)
                uclamp_rq_dec_id(rq, p, clamp_id);
}

static inline void uclamp_rq_reinc_id(struct rq *rq, struct task_struct *p,
                                      enum uclamp_id clamp_id)
{
        if (!p->uclamp[clamp_id].active)
                return;

        uclamp_rq_dec_id(rq, p, clamp_id);
        uclamp_rq_inc_id(rq, p, clamp_id);

        /*
         * Make sure to clear the idle flag if we've transiently reached 0
         * active tasks on rq.
         */
        if (clamp_id == UCLAMP_MAX && (rq->uclamp_flags & UCLAMP_FLAG_IDLE))
                rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
}

static inline void
uclamp_update_active(struct task_struct *p)
{
        enum uclamp_id clamp_id;
        struct rq_flags rf;
        struct rq *rq;

        /*
         * Lock the task and the rq where the task is (or was) queued.
         *
         * We might lock the (previous) rq of a !RUNNABLE task, but that's the
         * price to pay to safely serialize util_{min,max} updates with
         * enqueues, dequeues and migration operations.
         * This is the same locking schema used by __set_cpus_allowed_ptr().
         */
        rq = task_rq_lock(p, &rf);

        /*
         * Setting the clamp bucket is serialized by task_rq_lock().
         * If the task is not yet RUNNABLE and its task_struct is not
         * affecting a valid clamp bucket, the next time it's enqueued,
         * it will already see the updated clamp bucket value.
         */
        for_each_clamp_id(clamp_id)
                uclamp_rq_reinc_id(rq, p, clamp_id);

        task_rq_unlock(rq, p, &rf);
}

#ifdef CONFIG_UCLAMP_TASK_GROUP
static inline void
uclamp_update_active_tasks(struct cgroup_subsys_state *css)
{
        struct css_task_iter it;
        struct task_struct *p;

        css_task_iter_start(css, 0, &it);
        while ((p = css_task_iter_next(&it)))
                uclamp_update_active(p);
        css_task_iter_end(&it);
}

static void cpu_util_update_eff(struct cgroup_subsys_state *css);
static void uclamp_update_root_tg(void)
{
        struct task_group *tg = &root_task_group;

        uclamp_se_set(&tg->uclamp_req[UCLAMP_MIN],
                      sysctl_sched_uclamp_util_min, false);
        uclamp_se_set(&tg->uclamp_req[UCLAMP_MAX],
                      sysctl_sched_uclamp_util_max, false);

        rcu_read_lock();
        cpu_util_update_eff(&root_task_group.css);
        rcu_read_unlock();
}
#else
static void uclamp_update_root_tg(void) { }
#endif

int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
                                void *buffer, size_t *lenp, loff_t *ppos)
{
        bool update_root_tg = false;
        int old_min, old_max, old_min_rt;
        int result;

        mutex_lock(&uclamp_mutex);
        old_min = sysctl_sched_uclamp_util_min;
        old_max = sysctl_sched_uclamp_util_max;
        old_min_rt = sysctl_sched_uclamp_util_min_rt_default;

        result = proc_dointvec(table, write, buffer, lenp, ppos);
        if (result)
                goto undo;
        if (!write)
                goto done;

        if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
            sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE ||
            sysctl_sched_uclamp_util_min_rt_default > SCHED_CAPACITY_SCALE) {

                result = -EINVAL;
                goto undo;
        }

        if (old_min != sysctl_sched_uclamp_util_min) {
                uclamp_se_set(&uclamp_default[UCLAMP_MIN],
                              sysctl_sched_uclamp_util_min, false);
                update_root_tg = true;
        }
        if (old_max != sysctl_sched_uclamp_util_max) {
                uclamp_se_set(&uclamp_default[UCLAMP_MAX],
                              sysctl_sched_uclamp_util_max, false);
                update_root_tg = true;
        }

        if (update_root_tg) {
                static_branch_enable(&sched_uclamp_used);
                uclamp_update_root_tg();
        }

        if (old_min_rt != sysctl_sched_uclamp_util_min_rt_default) {
                static_branch_enable(&sched_uclamp_used);
                uclamp_sync_util_min_rt_default();
        }

        /*
         * We update all RUNNABLE tasks only when task groups are in use.
         * Otherwise, keep it simple and do just a lazy update at each next
         * task enqueue time.
         */

        goto done;

undo:
        sysctl_sched_uclamp_util_min = old_min;
        sysctl_sched_uclamp_util_max = old_max;
        sysctl_sched_uclamp_util_min_rt_default = old_min_rt;
done:
        mutex_unlock(&uclamp_mutex);

        return result;
}

static int uclamp_validate(struct task_struct *p,
                           const struct sched_attr *attr)
{
        int util_min = p->uclamp_req[UCLAMP_MIN].value;
        int util_max = p->uclamp_req[UCLAMP_MAX].value;

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
                util_min = attr->sched_util_min;

                if (util_min + 1 > SCHED_CAPACITY_SCALE + 1)
                        return -EINVAL;
        }

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
                util_max = attr->sched_util_max;

                if (util_max + 1 > SCHED_CAPACITY_SCALE + 1)
                        return -EINVAL;
        }

        if (util_min != -1 && util_max != -1 && util_min > util_max)
                return -EINVAL;

        /*
         * We have valid uclamp attributes; make sure uclamp is enabled.
         *
         * We need to do that here, because enabling static branches is a
         * blocking operation which obviously cannot be done while holding
         * scheduler locks.
         */
        static_branch_enable(&sched_uclamp_used);

        return 0;
}

static bool uclamp_reset(const struct sched_attr *attr,
                         enum uclamp_id clamp_id,
                         struct uclamp_se *uc_se)
{
        /* Reset on sched class change for a non user-defined clamp value. */
        if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)) &&
            !uc_se->user_defined)
                return true;

        /* Reset on sched_util_{min,max} == -1. */
        if (clamp_id == UCLAMP_MIN &&
            attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN &&
            attr->sched_util_min == -1) {
                return true;
        }

        if (clamp_id == UCLAMP_MAX &&
            attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX &&
            attr->sched_util_max == -1) {
                return true;
        }

        return false;
}

static void __setscheduler_uclamp(struct task_struct *p,
                                  const struct sched_attr *attr)
{
        enum uclamp_id clamp_id;

        for_each_clamp_id(clamp_id) {
                struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
                unsigned int value;

                if (!uclamp_reset(attr, clamp_id, uc_se))
                        continue;

                /*
                 * RT by default have a 100% boost value that could be modified
                 * at runtime.
                 */
                if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
                        value = sysctl_sched_uclamp_util_min_rt_default;
                else
                        value = uclamp_none(clamp_id);

                uclamp_se_set(uc_se, value, false);

        }

        if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
                return;

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN &&
            attr->sched_util_min != -1) {
                uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
                              attr->sched_util_min, true);
        }

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX &&
            attr->sched_util_max != -1) {
                uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
                              attr->sched_util_max, true);
        }
}

static void uclamp_fork(struct task_struct *p)
{
        enum uclamp_id clamp_id;

        /*
         * We don't need to hold task_rq_lock() when updating p->uclamp_* here
         * as the task is still at its early fork stages.
         */
        for_each_clamp_id(clamp_id)
                p->uclamp[clamp_id].active = false;

        if (likely(!p->sched_reset_on_fork))
                return;

        for_each_clamp_id(clamp_id) {
                uclamp_se_set(&p->uclamp_req[clamp_id],
                              uclamp_none(clamp_id), false);
        }
}

static void uclamp_post_fork(struct task_struct *p)
{
        uclamp_update_util_min_rt_default(p);
}

static void __init init_uclamp_rq(struct rq *rq)
{
        enum uclamp_id clamp_id;
        struct uclamp_rq *uc_rq = rq->uclamp;

        for_each_clamp_id(clamp_id) {
                uc_rq[clamp_id] = (struct uclamp_rq) {
                        .value = uclamp_none(clamp_id)
                };
        }

        rq->uclamp_flags = UCLAMP_FLAG_IDLE;
}

static void __init init_uclamp(void)
{
        struct uclamp_se uc_max = {};
        enum uclamp_id clamp_id;
        int cpu;

        for_each_possible_cpu(cpu)
                init_uclamp_rq(cpu_rq(cpu));

        for_each_clamp_id(clamp_id) {
                uclamp_se_set(&init_task.uclamp_req[clamp_id],
                              uclamp_none(clamp_id), false);
        }

        /* System defaults allow max clamp values for both indexes */
        uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX), false);
        for_each_clamp_id(clamp_id) {
                uclamp_default[clamp_id] = uc_max;
#ifdef CONFIG_UCLAMP_TASK_GROUP
                root_task_group.uclamp_req[clamp_id] = uc_max;
                root_task_group.uclamp[clamp_id] = uc_max;
#endif
        }
}

#else /* CONFIG_UCLAMP_TASK */
static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
static inline int uclamp_validate(struct task_struct *p,
                                  const struct sched_attr *attr)
{
        return -EOPNOTSUPP;
}
static void __setscheduler_uclamp(struct task_struct *p,
                                  const struct sched_attr *attr) { }
static inline void uclamp_fork(struct task_struct *p) { }
static inline void uclamp_post_fork(struct task_struct *p) { }
static inline void init_uclamp(void) { }
#endif /* CONFIG_UCLAMP_TASK */

bool sched_task_on_rq(struct task_struct *p)
{
        return task_on_rq_queued(p);
}

static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
        if (!(flags & ENQUEUE_NOCLOCK))
                update_rq_clock(rq);

        if (!(flags & ENQUEUE_RESTORE)) {
                sched_info_enqueue(rq, p);
                psi_enqueue(p, flags & ENQUEUE_WAKEUP);
        }

        uclamp_rq_inc(rq, p);
        p->sched_class->enqueue_task(rq, p, flags);

        if (sched_core_enabled(rq))
                sched_core_enqueue(rq, p);
}

static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
{
        if (sched_core_enabled(rq))
                sched_core_dequeue(rq, p);

        if (!(flags & DEQUEUE_NOCLOCK))
                update_rq_clock(rq);

        if (!(flags & DEQUEUE_SAVE)) {
                sched_info_dequeue(rq, p);
                psi_dequeue(p, flags & DEQUEUE_SLEEP);
        }

        uclamp_rq_dec(rq, p);
        p->sched_class->dequeue_task(rq, p, flags);
}

void activate_task(struct rq *rq, struct task_struct *p, int flags)
{
        enqueue_task(rq, p, flags);

        p->on_rq = TASK_ON_RQ_QUEUED;
}

void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
{
        p->on_rq = (flags & DEQUEUE_SLEEP) ? 0 : TASK_ON_RQ_MIGRATING;

        dequeue_task(rq, p, flags);
}

static inline int __normal_prio(int policy, int rt_prio, int nice)
{
        int prio;

        if (dl_policy(policy))
                prio = MAX_DL_PRIO - 1;
        else if (rt_policy(policy))
                prio = MAX_RT_PRIO - 1 - rt_prio;
        else
                prio = NICE_TO_PRIO(nice);

        return prio;
}

/*
 * Calculate the expected normal priority: i.e. priority
 * without taking RT-inheritance into account. Might be
 * boosted by interactivity modifiers. Changes upon fork,
 * setprio syscalls, and whenever the interactivity
 * estimator recalculates.
 */
static inline int normal_prio(struct task_struct *p)
{
        return __normal_prio(p->policy, p->rt_priority, PRIO_TO_NICE(p->static_prio));
}

/*
 * Calculate the current priority, i.e. the priority
 * taken into account by the scheduler. This value might
 * be boosted by RT tasks, or might be boosted by
 * interactivity modifiers. Will be RT if the task got
 * RT-boosted. If not then it returns p->normal_prio.
 */
static int effective_prio(struct task_struct *p)
{
        p->normal_prio = normal_prio(p);
        /*
         * If we are RT tasks or we were boosted to RT priority,
         * keep the priority unchanged. Otherwise, update priority
         * to the normal priority:
         */
        if (!rt_prio(p->prio))
                return p->normal_prio;
        return p->prio;
}

/**
 * task_curr - is this task currently executing on a CPU?
 * @p: the task in question.
 *
 * Return: 1 if the task is currently executing. 0 otherwise.
 */
inline int task_curr(const struct task_struct *p)
{
        return cpu_curr(task_cpu(p)) == p;
}

/*
 * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock,
 * use the balance_callback list if you want balancing.
 *
 * this means any call to check_class_changed() must be followed by a call to
 * balance_callback().
 */
static inline void check_class_changed(struct rq *rq, struct task_struct *p,
                                       const struct sched_class *prev_class,
                                       int oldprio)
{
        if (prev_class != p->sched_class) {
                if (prev_class->switched_from)
                        prev_class->switched_from(rq, p);

                p->sched_class->switched_to(rq, p);
        } else if (oldprio != p->prio || dl_task(p))
                p->sched_class->prio_changed(rq, p, oldprio);
}

void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
{
        if (p->sched_class == rq->curr->sched_class)
                rq->curr->sched_class->check_preempt_curr(rq, p, flags);
        else if (p->sched_class > rq->curr->sched_class)
                resched_curr(rq);

        /*
         * A queue event has occurred, and we're going to schedule.  In
         * this case, we can save a useless back to back clock update.
         */
        if (task_on_rq_queued(rq->curr) && test_tsk_need_resched(rq->curr))
                rq_clock_skip_update(rq);
}

#ifdef CONFIG_SMP

static void
__do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 flags);

static int __set_cpus_allowed_ptr(struct task_struct *p,
                                  const struct cpumask *new_mask,
                                  u32 flags);

static void migrate_disable_switch(struct rq *rq, struct task_struct *p)
{
        if (likely(!p->migration_disabled))
                return;

        if (p->cpus_ptr != &p->cpus_mask)
                return;

        /*
         * Violates locking rules! see comment in __do_set_cpus_allowed().
         */
        __do_set_cpus_allowed(p, cpumask_of(rq->cpu), SCA_MIGRATE_DISABLE);
}

void migrate_disable(void)
{
        struct task_struct *p = current;

        if (p->migration_disabled) {
                p->migration_disabled++;
                return;
        }

        preempt_disable();
        this_rq()->nr_pinned++;
        p->migration_disabled = 1;
        preempt_lazy_disable();
        preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_disable);

void migrate_enable(void)
{
        struct task_struct *p = current;

        if (p->migration_disabled > 1) {
                p->migration_disabled--;
                return;
        } else if (WARN_ON_ONCE(p->migration_disabled == 0)) {
                return;
        }

        /*
         * Ensure stop_task runs either before or after this, and that
         * __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule().
         */
        preempt_disable();
        if (p->cpus_ptr != &p->cpus_mask)
                __set_cpus_allowed_ptr(p, &p->cpus_mask, SCA_MIGRATE_ENABLE);
        /*
         * Mustn't clear migration_disabled() until cpus_ptr points back at the
         * regular cpus_mask, otherwise things that race (eg.
         * select_fallback_rq) get confused.
         */
        barrier();
        p->migration_disabled = 0;
        this_rq()->nr_pinned--;
        preempt_lazy_enable();
        preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_enable);

static inline bool rq_has_pinned_tasks(struct rq *rq)
{
        return rq->nr_pinned;
}

/*
 * Per-CPU kthreads are allowed to run on !active && online CPUs, see
 * __set_cpus_allowed_ptr() and select_fallback_rq().
 */
static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
{
        /* When not in the task's cpumask, no point in looking further. */
        if (!cpumask_test_cpu(cpu, p->cpus_ptr))
                return false;

        /* migrate_disabled() must be allowed to finish. */
        if (is_migration_disabled(p))
                return cpu_online(cpu);

        /* Non kernel threads are not allowed during either online or offline. */
        if (!(p->flags & PF_KTHREAD))
                return cpu_active(cpu) && task_cpu_possible(cpu, p);

        /* KTHREAD_IS_PER_CPU is always allowed. */
        if (kthread_is_per_cpu(p))
                return cpu_online(cpu);

        /* Regular kernel threads don't get to stay during offline. */
        if (cpu_dying(cpu))
                return false;

        /* But are allowed during online. */
        return cpu_online(cpu);
}

/*
 * This is how migration works:
 *
 * 1) we invoke migration_cpu_stop() on the target CPU using
 *    stop_one_cpu().
 * 2) stopper starts to run (implicitly forcing the migrated thread
 *    off the CPU)
 * 3) it checks whether the migrated task is still in the wrong runqueue.
 * 4) if it's in the wrong runqueue then the migration thread removes
 *    it and puts it into the right queue.
 * 5) stopper completes and stop_one_cpu() returns and the migration
 *    is done.
 */

/*
 * move_queued_task - move a queued task to new rq.
 *
 * Returns (locked) new rq. Old rq's lock is released.
 */
static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
                                   struct task_struct *p, int new_cpu)
{
        lockdep_assert_rq_held(rq);

        deactivate_task(rq, p, DEQUEUE_NOCLOCK);
        set_task_cpu(p, new_cpu);
        rq_unlock(rq, rf);

        rq = cpu_rq(new_cpu);

        rq_lock(rq, rf);
        BUG_ON(task_cpu(p) != new_cpu);
        activate_task(rq, p, 0);
        check_preempt_curr(rq, p, 0);

        return rq;
}

struct migration_arg {
        struct task_struct              *task;
        int                             dest_cpu;
        struct set_affinity_pending     *pending;
};

/*
 * @refs: number of wait_for_completion()
 * @stop_pending: is @stop_work in use
 */
struct set_affinity_pending {
        refcount_t              refs;
        unsigned int            stop_pending;
        struct completion       done;
        struct cpu_stop_work    stop_work;
        struct migration_arg    arg;
};

/*
 * Move (not current) task off this CPU, onto the destination CPU. We're doing
 * this because either it can't run here any more (set_cpus_allowed()
 * away from this CPU, or CPU going down), or because we're
 * attempting to rebalance this task on exec (sched_exec).
 *
 * So we race with normal scheduler movements, but that's OK, as long
 * as the task is no longer on this CPU.
 */
static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
                                 struct task_struct *p, int dest_cpu)
{
        /* Affinity changed (again). */
        if (!is_cpu_allowed(p, dest_cpu))
                return rq;

        update_rq_clock(rq);
        rq = move_queued_task(rq, rf, p, dest_cpu);

        return rq;
}

/*
 * migration_cpu_stop - this will be executed by a highprio stopper thread
 * and performs thread migration by bumping thread off CPU then
 * 'pushing' onto another runqueue.
 */
static int migration_cpu_stop(void *data)
{
        struct migration_arg *arg = data;
        struct set_affinity_pending *pending = arg->pending;
        struct task_struct *p = arg->task;
        struct rq *rq = this_rq();
        bool complete = false;
        struct rq_flags rf;

        /*
         * The original target CPU might have gone down and we might
         * be on another CPU but it doesn't matter.
         */
        local_irq_save(rf.flags);
        /*
         * We need to explicitly wake pending tasks before running
         * __migrate_task() such that we will not miss enforcing cpus_ptr
         * during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test.
         */
        flush_smp_call_function_from_idle();

        raw_spin_lock(&p->pi_lock);
        rq_lock(rq, &rf);

        /*
         * If we were passed a pending, then ->stop_pending was set, thus
         * p->migration_pending must have remained stable.
         */
        WARN_ON_ONCE(pending && pending != p->migration_pending);

        /*
         * If task_rq(p) != rq, it cannot be migrated here, because we're
         * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
         * we're holding p->pi_lock.
         */
        if (task_rq(p) == rq) {
                if (is_migration_disabled(p))
                        goto out;

                if (pending) {
                        p->migration_pending = NULL;
                        complete = true;

                        if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask))
                                goto out;
                }

                if (task_on_rq_queued(p))
                        rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
                else
                        p->wake_cpu = arg->dest_cpu;

                /*
                 * XXX __migrate_task() can fail, at which point we might end
                 * up running on a dodgy CPU, AFAICT this can only happen
                 * during CPU hotplug, at which point we'll get pushed out
                 * anyway, so it's probably not a big deal.
                 */

        } else if (pending) {
                /*
                 * This happens when we get migrated between migrate_enable()'s
                 * preempt_enable() and scheduling the stopper task. At that
                 * point we're a regular task again and not current anymore.
                 *
                 * A !PREEMPT kernel has a giant hole here, which makes it far
                 * more likely.
                 */

                /*
                 * The task moved before the stopper got to run. We're holding
                 * ->pi_lock, so the allowed mask is stable - if it got
                 * somewhere allowed, we're done.
                 */
                if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) {
                        p->migration_pending = NULL;
                        complete = true;
                        goto out;
                }

                /*
                 * When migrate_enable() hits a rq mis-match we can't reliably
                 * determine is_migration_disabled() and so have to chase after
                 * it.
                 */
                WARN_ON_ONCE(!pending->stop_pending);
                task_rq_unlock(rq, p, &rf);
                stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
                                    &pending->arg, &pending->stop_work);
                return 0;
        }
out:
        if (pending)
                pending->stop_pending = false;
        task_rq_unlock(rq, p, &rf);

        if (complete)
                complete_all(&pending->done);

        return 0;
}

int push_cpu_stop(void *arg)
{
        struct rq *lowest_rq = NULL, *rq = this_rq();
        struct task_struct *p = arg;

        raw_spin_lock_irq(&p->pi_lock);
        raw_spin_rq_lock(rq);

        if (task_rq(p) != rq)
                goto out_unlock;

        if (is_migration_disabled(p)) {
                p->migration_flags |= MDF_PUSH;
                goto out_unlock;
        }

        p->migration_flags &= ~MDF_PUSH;

        if (p->sched_class->find_lock_rq)
                lowest_rq = p->sched_class->find_lock_rq(p, rq);

        if (!lowest_rq)
                goto out_unlock;

        // XXX validate p is still the highest prio task
        if (task_rq(p) == rq) {
                deactivate_task(rq, p, 0);
                set_task_cpu(p, lowest_rq->cpu);
                activate_task(lowest_rq, p, 0);
                resched_curr(lowest_rq);
        }

        double_unlock_balance(rq, lowest_rq);

out_unlock:
        rq->push_busy = false;
        raw_spin_rq_unlock(rq);
        raw_spin_unlock_irq(&p->pi_lock);

        put_task_struct(p);
        return 0;
}

/*
 * sched_class::set_cpus_allowed must do the below, but is not required to
 * actually call this function.
 */
void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_mask, u32 flags)
{
        if (flags & (SCA_MIGRATE_ENABLE | SCA_MIGRATE_DISABLE)) {
                p->cpus_ptr = new_mask;
                return;
        }

        cpumask_copy(&p->cpus_mask, new_mask);
        p->nr_cpus_allowed = cpumask_weight(new_mask);
}

static void
__do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 flags)
{
        struct rq *rq = task_rq(p);
        bool queued, running;

        /*
         * This here violates the locking rules for affinity, since we're only
         * supposed to change these variables while holding both rq->lock and
         * p->pi_lock.
         *
         * HOWEVER, it magically works, because ttwu() is the only code that
         * accesses these variables under p->pi_lock and only does so after
         * smp_cond_load_acquire(&p->on_cpu, !VAL), and we're in __schedule()
         * before finish_task().
         *
         * XXX do further audits, this smells like something putrid.
         */
        if (flags & SCA_MIGRATE_DISABLE)
                SCHED_WARN_ON(!p->on_cpu);
        else
                lockdep_assert_held(&p->pi_lock);

        queued = task_on_rq_queued(p);
        running = task_current(rq, p);

        if (queued) {
                /*
                 * Because __kthread_bind() calls this on blocked tasks without
                 * holding rq->lock.
                 */
                lockdep_assert_rq_held(rq);
                dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
        }
        if (running)
                put_prev_task(rq, p);

        p->sched_class->set_cpus_allowed(p, new_mask, flags);

        if (queued)
                enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
        if (running)
                set_next_task(rq, p);
}

void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
{
        __do_set_cpus_allowed(p, new_mask, 0);
}

int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
                      int node)
{
        cpumask_t *user_mask;
        unsigned long flags;

        /*
         * Always clear dst->user_cpus_ptr first as their user_cpus_ptr's
         * may differ by now due to racing.
         */
        dst->user_cpus_ptr = NULL;

        /*
         * This check is racy and losing the race is a valid situation.
         * It is not worth the extra overhead of taking the pi_lock on
         * every fork/clone.
         */
        if (data_race(!src->user_cpus_ptr))
                return 0;

        user_mask = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
        if (!user_mask)
                return -ENOMEM;

        /*
         * Use pi_lock to protect content of user_cpus_ptr
         *
         * Though unlikely, user_cpus_ptr can be reset to NULL by a concurrent
         * do_set_cpus_allowed().
         */
        raw_spin_lock_irqsave(&src->pi_lock, flags);
        if (src->user_cpus_ptr) {
                swap(dst->user_cpus_ptr, user_mask);
                cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
        }
        raw_spin_unlock_irqrestore(&src->pi_lock, flags);

        if (unlikely(user_mask))
                kfree(user_mask);

        return 0;
}

static inline struct cpumask *clear_user_cpus_ptr(struct task_struct *p)
{
        struct cpumask *user_mask = NULL;

        swap(p->user_cpus_ptr, user_mask);

        return user_mask;
}

void release_user_cpus_ptr(struct task_struct *p)
{
        kfree(clear_user_cpus_ptr(p));
}

/*
 * This function is wildly self concurrent; here be dragons.
 *
 *
 * When given a valid mask, __set_cpus_allowed_ptr() must block until the
 * designated task is enqueued on an allowed CPU. If that task is currently
 * running, we have to kick it out using the CPU stopper.
 *
 * Migrate-Disable comes along and tramples all over our nice sandcastle.
 * Consider:
 *
 *     Initial conditions: P0->cpus_mask = [0, 1]
 *
 *     P0@CPU0                  P1
 *
 *     migrate_disable();
 *     <preempted>
 *                              set_cpus_allowed_ptr(P0, [1]);
 *
 * P1 *cannot* return from this set_cpus_allowed_ptr() call until P0 executes
 * its outermost migrate_enable() (i.e. it exits its Migrate-Disable region).
 * This means we need the following scheme:
 *
 *     P0@CPU0                  P1
 *
 *     migrate_disable();
 *     <preempted>
 *                              set_cpus_allowed_ptr(P0, [1]);
 *                                <blocks>
 *     <resumes>
 *     migrate_enable();
 *       __set_cpus_allowed_ptr();
 *       <wakes local stopper>
 *                         `--> <woken on migration completion>
 *
 * Now the fun stuff: there may be several P1-like tasks, i.e. multiple
 * concurrent set_cpus_allowed_ptr(P0, [*]) calls. CPU affinity changes of any
 * task p are serialized by p->pi_lock, which we can leverage: the one that
 * should come into effect at the end of the Migrate-Disable region is the last
 * one. This means we only need to track a single cpumask (i.e. p->cpus_mask),
 * but we still need to properly signal those waiting tasks at the appropriate
 * moment.
 *
 * This is implemented using struct set_affinity_pending. The first
 * __set_cpus_allowed_ptr() caller within a given Migrate-Disable region will
 * setup an instance of that struct and install it on the targeted task_struct.
 * Any and all further callers will reuse that instance. Those then wait for
 * a completion signaled at the tail of the CPU stopper callback (1), triggered
 * on the end of the Migrate-Disable region (i.e. outermost migrate_enable()).
 *
 *
 * (1) In the cases covered above. There is one more where the completion is
 * signaled within affine_move_task() itself: when a subsequent affinity request
 * occurs after the stopper bailed out due to the targeted task still being
 * Migrate-Disable. Consider:
 *
 *     Initial conditions: P0->cpus_mask = [0, 1]
 *
 *     CPU0               P1                            P2
 *     <P0>
 *       migrate_disable();
 *       <preempted>
 *                        set_cpus_allowed_ptr(P0, [1]);
 *                          <blocks>
 *     <migration/0>
 *       migration_cpu_stop()
 *         is_migration_disabled()
 *           <bails>
 *                                                       set_cpus_allowed_ptr(P0, [0, 1]);
 *                                                         <signal completion>
 *                          <awakes>
 *
 * Note that the above is safe vs a concurrent migrate_enable(), as any
 * pending affinity completion is preceded by an uninstallation of
 * p->migration_pending done with p->pi_lock held.
 */
static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flags *rf,
                            int dest_cpu, unsigned int flags)
{
        struct set_affinity_pending my_pending = { }, *pending = NULL;
        bool stop_pending, complete = false;

        /* Can the task run on the task's current CPU? If so, we're done */
        if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
                struct task_struct *push_task = NULL;

                if ((flags & SCA_MIGRATE_ENABLE) &&
                    (p->migration_flags & MDF_PUSH) && !rq->push_busy) {
                        rq->push_busy = true;
                        push_task = get_task_struct(p);
                }

                /*
                 * If there are pending waiters, but no pending stop_work,
                 * then complete now.
                 */
                pending = p->migration_pending;
                if (pending && !pending->stop_pending) {
                        p->migration_pending = NULL;
                        complete = true;
                }

                task_rq_unlock(rq, p, rf);

                if (push_task) {
                        stop_one_cpu_nowait(rq->cpu, push_cpu_stop,
                                            p, &rq->push_work);
                }

                if (complete)
                        complete_all(&pending->done);

                return 0;
        }

        if (!(flags & SCA_MIGRATE_ENABLE)) {
                /* serialized by p->pi_lock */
                if (!p->migration_pending) {
                        /* Install the request */
                        refcount_set(&my_pending.refs, 1);
                        init_completion(&my_pending.done);
                        my_pending.arg = (struct migration_arg) {
                                .task = p,
                                .dest_cpu = dest_cpu,
                                .pending = &my_pending,
                        };

                        p->migration_pending = &my_pending;
                } else {
                        pending = p->migration_pending;
                        refcount_inc(&pending->refs);
                        /*
                         * Affinity has changed, but we've already installed a
                         * pending. migration_cpu_stop() *must* see this, else
                         * we risk a completion of the pending despite having a
                         * task on a disallowed CPU.
                         *
                         * Serialized by p->pi_lock, so this is safe.
                         */
                        pending->arg.dest_cpu = dest_cpu;
                }
        }
        pending = p->migration_pending;
        /*
         * - !MIGRATE_ENABLE:
         *   we'll have installed a pending if there wasn't one already.
         *
         * - MIGRATE_ENABLE:
         *   we're here because the current CPU isn't matching anymore,
         *   the only way that can happen is because of a concurrent
         *   set_cpus_allowed_ptr() call, which should then still be
         *   pending completion.
         *
         * Either way, we really should have a @pending here.
         */
        if (WARN_ON_ONCE(!pending)) {
                task_rq_unlock(rq, p, rf);
                return -EINVAL;
        }

        if (task_running(rq, p) || READ_ONCE(p->__state) == TASK_WAKING) {
                /*
                 * MIGRATE_ENABLE gets here because 'p == current', but for
                 * anything else we cannot do is_migration_disabled(), punt
                 * and have the stopper function handle it all race-free.
                 */
                stop_pending = pending->stop_pending;
                if (!stop_pending)
                        pending->stop_pending = true;

                if (flags & SCA_MIGRATE_ENABLE)
                        p->migration_flags &= ~MDF_PUSH;

                task_rq_unlock(rq, p, rf);

                if (!stop_pending) {
                        stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
                                            &pending->arg, &pending->stop_work);
                }

                if (flags & SCA_MIGRATE_ENABLE)
                        return 0;
        } else {

                if (!is_migration_disabled(p)) {
                        if (task_on_rq_queued(p))
                                rq = move_queued_task(rq, rf, p, dest_cpu);

                        if (!pending->stop_pending) {
                                p->migration_pending = NULL;
                                complete = true;
                        }
                }
                task_rq_unlock(rq, p, rf);

                if (complete)
                        complete_all(&pending->done);
        }

        wait_for_completion(&pending->done);

        if (refcount_dec_and_test(&pending->refs))
                wake_up_var(&pending->refs); /* No UaF, just an address */

        /*
         * Block the original owner of &pending until all subsequent callers
         * have seen the completion and decremented the refcount
         */
        wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs));

        /* ARGH */
        WARN_ON_ONCE(my_pending.stop_pending);

        return 0;
}

/*
 * Called with both p->pi_lock and rq->lock held; drops both before returning.
 */
static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
                                         const struct cpumask *new_mask,
                                         u32 flags,
                                         struct rq *rq,
                                         struct rq_flags *rf)
        __releases(rq->lock)
        __releases(p->pi_lock)
{
        const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
        const struct cpumask *cpu_valid_mask = cpu_active_mask;
        bool kthread = p->flags & PF_KTHREAD;
        struct cpumask *user_mask = NULL;
        unsigned int dest_cpu;
        int ret = 0;

        update_rq_clock(rq);

        if (kthread || is_migration_disabled(p)) {
                /*
                 * Kernel threads are allowed on online && !active CPUs,
                 * however, during cpu-hot-unplug, even these might get pushed
                 * away if not KTHREAD_IS_PER_CPU.
                 *
                 * Specifically, migration_disabled() tasks must not fail the
                 * cpumask_any_and_distribute() pick below, esp. so on
                 * SCA_MIGRATE_ENABLE, otherwise we'll not call
                 * set_cpus_allowed_common() and actually reset p->cpus_ptr.
                 */
                cpu_valid_mask = cpu_online_mask;
        }

        if (!kthread && !cpumask_subset(new_mask, cpu_allowed_mask)) {
                ret = -EINVAL;
                goto out;
        }

        /*
         * Must re-check here, to close a race against __kthread_bind(),
         * sched_setaffinity() is not guaranteed to observe the flag.
         */
        if ((flags & SCA_CHECK) && (p->flags & PF_NO_SETAFFINITY)) {
                ret = -EINVAL;
                goto out;
        }

        if (!(flags & SCA_MIGRATE_ENABLE)) {
                if (cpumask_equal(&p->cpus_mask, new_mask))
                        goto out;

                if (WARN_ON_ONCE(p == current &&
                                 is_migration_disabled(p) &&
                                 !cpumask_test_cpu(task_cpu(p), new_mask))) {
                        ret = -EBUSY;
                        goto out;
                }
        }

        /*
         * Picking a ~random cpu helps in cases where we are changing affinity
         * for groups of tasks (ie. cpuset), so that load balancing is not
         * immediately required to distribute the tasks within their new mask.
         */
        dest_cpu = cpumask_any_and_distribute(cpu_valid_mask, new_mask);
        if (dest_cpu >= nr_cpu_ids) {
                ret = -EINVAL;
                goto out;
        }

        __do_set_cpus_allowed(p, new_mask, flags);

        if (flags & SCA_USER)
                user_mask = clear_user_cpus_ptr(p);

        ret = affine_move_task(rq, p, rf, dest_cpu, flags);

        kfree(user_mask);

        return ret;

out:
        task_rq_unlock(rq, p, rf);

        return ret;
}

/*
 * Change a given task's CPU affinity. Migrate the thread to a
 * proper CPU and schedule it away if the CPU it's executing on
 * is removed from the allowed bitmask.
 *
 * NOTE: the caller must have a valid reference to the task, the
 * task must not exit() & deallocate itself prematurely. The
 * call is not atomic; no spinlocks may be held.
 */
static int __set_cpus_allowed_ptr(struct task_struct *p,
                                  const struct cpumask *new_mask, u32 flags)
{
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(p, &rf);
        return __set_cpus_allowed_ptr_locked(p, new_mask, flags, rq, &rf);
}

int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
{
        return __set_cpus_allowed_ptr(p, new_mask, 0);
}
EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);

/*
 * Change a given task's CPU affinity to the intersection of its current
 * affinity mask and @subset_mask, writing the resulting mask to @new_mask
 * and pointing @p->user_cpus_ptr to a copy of the old mask.
 * If the resulting mask is empty, leave the affinity unchanged and return
 * -EINVAL.
 */
static int restrict_cpus_allowed_ptr(struct task_struct *p,
                                     struct cpumask *new_mask,
                                     const struct cpumask *subset_mask)
{
        struct cpumask *user_mask = NULL;
        struct rq_flags rf;
        struct rq *rq;
        int err;

        if (!p->user_cpus_ptr) {
                user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
                if (!user_mask)
                        return -ENOMEM;
        }

        rq = task_rq_lock(p, &rf);

        /*
         * Forcefully restricting the affinity of a deadline task is
         * likely to cause problems, so fail and noisily override the
         * mask entirely.
         */
        if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
                err = -EPERM;
                goto err_unlock;
        }

        if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
                err = -EINVAL;
                goto err_unlock;
        }

        /*
         * We're about to butcher the task affinity, so keep track of what
         * the user asked for in case we're able to restore it later on.
         */
        if (user_mask) {
                cpumask_copy(user_mask, p->cpus_ptr);
                p->user_cpus_ptr = user_mask;
        }

        return __set_cpus_allowed_ptr_locked(p, new_mask, 0, rq, &rf);

err_unlock:
        task_rq_unlock(rq, p, &rf);
        kfree(user_mask);
        return err;
}

/*
 * Restrict the CPU affinity of task @p so that it is a subset of
 * task_cpu_possible_mask() and point @p->user_cpu_ptr to a copy of the
 * old affinity mask. If the resulting mask is empty, we warn and walk
 * up the cpuset hierarchy until we find a suitable mask.
 */
void force_compatible_cpus_allowed_ptr(struct task_struct *p)
{
        cpumask_var_t new_mask;
        const struct cpumask *override_mask = task_cpu_possible_mask(p);

        alloc_cpumask_var(&new_mask, GFP_KERNEL);

        /*
         * __migrate_task() can fail silently in the face of concurrent
         * offlining of the chosen destination CPU, so take the hotplug
         * lock to ensure that the migration succeeds.
         */
        cpus_read_lock();
        if (!cpumask_available(new_mask))
                goto out_set_mask;

        if (!restrict_cpus_allowed_ptr(p, new_mask, override_mask))
                goto out_free_mask;

        /*
         * We failed to find a valid subset of the affinity mask for the
         * task, so override it based on its cpuset hierarchy.
         */
        cpuset_cpus_allowed(p, new_mask);
        override_mask = new_mask;

out_set_mask:
        if (printk_ratelimit()) {
                printk_deferred("Overriding affinity for process %d (%s) to CPUs %*pbl\n",
                                task_pid_nr(p), p->comm,
                                cpumask_pr_args(override_mask));
        }

        WARN_ON(set_cpus_allowed_ptr(p, override_mask));
out_free_mask:
        cpus_read_unlock();
        free_cpumask_var(new_mask);
}

static int
__sched_setaffinity(struct task_struct *p, const struct cpumask *mask);

/*
 * Restore the affinity of a task @p which was previously restricted by a
 * call to force_compatible_cpus_allowed_ptr(). This will clear (and free)
 * @p->user_cpus_ptr.
 *
 * It is the caller's responsibility to serialise this with any calls to
 * force_compatible_cpus_allowed_ptr(@p).
 */
void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
{
        struct cpumask *user_mask = p->user_cpus_ptr;
        unsigned long flags;

        /*
         * Try to restore the old affinity mask. If this fails, then
         * we free the mask explicitly to avoid it being inherited across
         * a subsequent fork().
         */
        if (!user_mask || !__sched_setaffinity(p, user_mask))
                return;

        raw_spin_lock_irqsave(&p->pi_lock, flags);
        user_mask = clear_user_cpus_ptr(p);
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);

        kfree(user_mask);
}

void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
{
#ifdef CONFIG_SCHED_DEBUG
        unsigned int state = READ_ONCE(p->__state);

        /*
         * We should never call set_task_cpu() on a blocked task,
         * ttwu() will sort out the placement.
         */
        WARN_ON_ONCE(state != TASK_RUNNING && state != TASK_WAKING && !p->on_rq);

        /*
         * Migrating fair class task must have p->on_rq = TASK_ON_RQ_MIGRATING,
         * because schedstat_wait_{start,end} rebase migrating task's wait_start
         * time relying on p->on_rq.
         */
        WARN_ON_ONCE(state == TASK_RUNNING &&
                     p->sched_class == &fair_sched_class &&
                     (p->on_rq && !task_on_rq_migrating(p)));

#ifdef CONFIG_LOCKDEP
        /*
         * The caller should hold either p->pi_lock or rq->lock, when changing
         * a task's CPU. ->pi_lock for waking tasks, rq->lock for runnable tasks.
         *
         * sched_move_task() holds both and thus holding either pins the cgroup,
         * see task_group().
         *
         * Furthermore, all task_rq users should acquire both locks, see
         * task_rq_lock().
         */
        WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
                                      lockdep_is_held(__rq_lockp(task_rq(p)))));
#endif
        /*
         * Clearly, migrating tasks to offline CPUs is a fairly daft thing.
         */
        WARN_ON_ONCE(!cpu_online(new_cpu));

        WARN_ON_ONCE(is_migration_disabled(p));
#endif

        trace_sched_migrate_task(p, new_cpu);

        if (task_cpu(p) != new_cpu) {
                if (p->sched_class->migrate_task_rq)
                        p->sched_class->migrate_task_rq(p, new_cpu);
                p->se.nr_migrations++;
                rseq_migrate(p);
                perf_event_task_migrate(p);
        }

        __set_task_cpu(p, new_cpu);
}

#ifdef CONFIG_NUMA_BALANCING
static void __migrate_swap_task(struct task_struct *p, int cpu)
{
        if (task_on_rq_queued(p)) {
                struct rq *src_rq, *dst_rq;
                struct rq_flags srf, drf;

                src_rq = task_rq(p);
                dst_rq = cpu_rq(cpu);

                rq_pin_lock(src_rq, &srf);
                rq_pin_lock(dst_rq, &drf);

                deactivate_task(src_rq, p, 0);
                set_task_cpu(p, cpu);
                activate_task(dst_rq, p, 0);
                check_preempt_curr(dst_rq, p, 0);

                rq_unpin_lock(dst_rq, &drf);
                rq_unpin_lock(src_rq, &srf);

        } else {
                /*
                 * Task isn't running anymore; make it appear like we migrated
                 * it before it went to sleep. This means on wakeup we make the
                 * previous CPU our target instead of where it really is.
                 */
                p->wake_cpu = cpu;
        }
}

struct migration_swap_arg {
        struct task_struct *src_task, *dst_task;
        int src_cpu, dst_cpu;
};

static int migrate_swap_stop(void *data)
{
        struct migration_swap_arg *arg = data;
        struct rq *src_rq, *dst_rq;
        int ret = -EAGAIN;

        if (!cpu_active(arg->src_cpu) || !cpu_active(arg->dst_cpu))
                return -EAGAIN;

        src_rq = cpu_rq(arg->src_cpu);
        dst_rq = cpu_rq(arg->dst_cpu);

        double_raw_lock(&arg->src_task->pi_lock,
                        &arg->dst_task->pi_lock);
        double_rq_lock(src_rq, dst_rq);

        if (task_cpu(arg->dst_task) != arg->dst_cpu)
                goto unlock;

        if (task_cpu(arg->src_task) != arg->src_cpu)
                goto unlock;

        if (!cpumask_test_cpu(arg->dst_cpu, arg->src_task->cpus_ptr))
                goto unlock;

        if (!cpumask_test_cpu(arg->src_cpu, arg->dst_task->cpus_ptr))
                goto unlock;

        __migrate_swap_task(arg->src_task, arg->dst_cpu);
        __migrate_swap_task(arg->dst_task, arg->src_cpu);

        ret = 0;

unlock:
        double_rq_unlock(src_rq, dst_rq);
        raw_spin_unlock(&arg->dst_task->pi_lock);
        raw_spin_unlock(&arg->src_task->pi_lock);

        return ret;
}

/*
 * Cross migrate two tasks
 */
int migrate_swap(struct task_struct *cur, struct task_struct *p,
                int target_cpu, int curr_cpu)
{
        struct migration_swap_arg arg;
        int ret = -EINVAL;

        arg = (struct migration_swap_arg){
                .src_task = cur,
                .src_cpu = curr_cpu,
                .dst_task = p,
                .dst_cpu = target_cpu,
        };

        if (arg.src_cpu == arg.dst_cpu)
                goto out;

        /*
         * These three tests are all lockless; this is OK since all of them
         * will be re-checked with proper locks held further down the line.
         */
        if (!cpu_active(arg.src_cpu) || !cpu_active(arg.dst_cpu))
                goto out;

        if (!cpumask_test_cpu(arg.dst_cpu, arg.src_task->cpus_ptr))
                goto out;

        if (!cpumask_test_cpu(arg.src_cpu, arg.dst_task->cpus_ptr))
                goto out;

        trace_sched_swap_numa(cur, arg.src_cpu, p, arg.dst_cpu);
        ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);

out:
        return ret;
}
#endif /* CONFIG_NUMA_BALANCING */

/*
 * wait_task_inactive - wait for a thread to unschedule.
 *
 * If @match_state is nonzero, it's the @p->state value just checked and
 * not expected to change.  If it changes, i.e. @p might have woken up,
 * then return zero.  When we succeed in waiting for @p to be off its CPU,
 * we return a positive number (its total switch count).  If a second call
 * a short while later returns the same number, the caller can be sure that
 * @p has remained unscheduled the whole time.
 *
 * The caller must ensure that the task *will* unschedule sometime soon,
 * else this function might spin for a *long* time. This function can't
 * be called with interrupts off, or it may introduce deadlock with
 * smp_call_function() if an IPI is sent by the same process we are
 * waiting to become inactive.
 */
unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state)
{
        int running, queued;
        struct rq_flags rf;
        unsigned long ncsw;
        struct rq *rq;

        for (;;) {
                /*
                 * We do the initial early heuristics without holding
                 * any task-queue locks at all. We'll only try to get
                 * the runqueue lock when things look like they will
                 * work out!
                 */
                rq = task_rq(p);

                /*
                 * If the task is actively running on another CPU
                 * still, just relax and busy-wait without holding
                 * any locks.
                 *
                 * NOTE! Since we don't hold any locks, it's not
                 * even sure that "rq" stays as the right runqueue!
                 * But we don't care, since "task_running()" will
                 * return false if the runqueue has changed and p
                 * is actually now running somewhere else!
                 */
                while (task_running(rq, p)) {
                        if (match_state && !task_match_state_lock(p, match_state))
                                return 0;
                        cpu_relax();
                }

                /*
                 * Ok, time to look more closely! We need the rq
                 * lock now, to be *sure*. If we're wrong, we'll
                 * just go back and repeat.
                 */
                rq = task_rq_lock(p, &rf);
                trace_sched_wait_task(p);
                running = task_running(rq, p);
                queued = task_on_rq_queued(p);
                ncsw = 0;
                if (!match_state || task_match_state_or_saved(p, match_state))
                        ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
                task_rq_unlock(rq, p, &rf);

                /*
                 * If it changed from the expected state, bail out now.
                 */
                if (unlikely(!ncsw))
                        break;

                /*
                 * Was it really running after all now that we
                 * checked with the proper locks actually held?
                 *
                 * Oops. Go back and try again..
                 */
                if (unlikely(running)) {
                        cpu_relax();
                        continue;
                }

                /*
                 * It's not enough that it's not actively running,
                 * it must be off the runqueue _entirely_, and not
                 * preempted!
                 *
                 * So if it was still runnable (but just not actively
                 * running right now), it's preempted, and we should
                 * yield - it could be a while.
                 */
                if (unlikely(queued)) {
                        ktime_t to = NSEC_PER_SEC / HZ;

                        set_current_state(TASK_UNINTERRUPTIBLE);
                        schedule_hrtimeout(&to, HRTIMER_MODE_REL_HARD);
                        continue;
                }

                /*
                 * Ahh, all good. It wasn't running, and it wasn't
                 * runnable, which means that it will never become
                 * running in the future either. We're all done!
                 */
                break;
        }

        return ncsw;
}

/***
 * kick_process - kick a running thread to enter/exit the kernel
 * @p: the to-be-kicked thread
 *
 * Cause a process which is running on another CPU to enter
 * kernel-mode, without any delay. (to get signals handled.)
 *
 * NOTE: this function doesn't have to take the runqueue lock,
 * because all it wants to ensure is that the remote task enters
 * the kernel. If the IPI races and the task has been migrated
 * to another CPU then no harm is done and the purpose has been
 * achieved as well.
 */
void kick_process(struct task_struct *p)
{
        int cpu;

        preempt_disable();
        cpu = task_cpu(p);
        if ((cpu != smp_processor_id()) && task_curr(p))
                smp_send_reschedule(cpu);
        preempt_enable();
}
EXPORT_SYMBOL_GPL(kick_process);

/*
 * ->cpus_ptr is protected by both rq->lock and p->pi_lock
 *
 * A few notes on cpu_active vs cpu_online:
 *
 *  - cpu_active must be a subset of cpu_online
 *
 *  - on CPU-up we allow per-CPU kthreads on the online && !active CPU,
 *    see __set_cpus_allowed_ptr(). At this point the newly online
 *    CPU isn't yet part of the sched domains, and balancing will not
 *    see it.
 *
 *  - on CPU-down we clear cpu_active() to mask the sched domains and
 *    avoid the load balancer to place new tasks on the to be removed
 *    CPU. Existing tasks will remain running there and will be taken
 *    off.
 *
 * This means that fallback selection must not select !active CPUs.
 * And can assume that any active CPU must be online. Conversely
 * select_task_rq() below may allow selection of !active CPUs in order
 * to satisfy the above rules.
 */
static int select_fallback_rq(int cpu, struct task_struct *p)
{
        int nid = cpu_to_node(cpu);
        const struct cpumask *nodemask = NULL;
        enum { cpuset, possible, fail } state = cpuset;
        int dest_cpu;

        /*
         * If the node that the CPU is on has been offlined, cpu_to_node()
         * will return -1. There is no CPU on the node, and we should
         * select the CPU on the other node.
         */
        if (nid != -1) {
                nodemask = cpumask_of_node(nid);

                /* Look for allowed, online CPU in same node. */
                for_each_cpu(dest_cpu, nodemask) {
                        if (is_cpu_allowed(p, dest_cpu))
                                return dest_cpu;
                }
        }

        for (;;) {
                /* Any allowed, online CPU? */
                for_each_cpu(dest_cpu, p->cpus_ptr) {
                        if (!is_cpu_allowed(p, dest_cpu))
                                continue;

                        goto out;
                }

                /* No more Mr. Nice Guy. */
                switch (state) {
                case cpuset:
                        if (cpuset_cpus_allowed_fallback(p)) {
                                state = possible;
                                break;
                        }
                        fallthrough;
                case possible:
                        /*
                         * XXX When called from select_task_rq() we only
                         * hold p->pi_lock and again violate locking order.
                         *
                         * More yuck to audit.
                         */
                        do_set_cpus_allowed(p, task_cpu_possible_mask(p));
                        state = fail;
                        break;
                case fail:
                        BUG();
                        break;
                }
        }

out:
        if (state != cpuset) {
                /*
                 * Don't tell them about moving exiting tasks or
                 * kernel threads (both mm NULL), since they never
                 * leave kernel.
                 */
                if (p->mm && printk_ratelimit()) {
                        printk_deferred("process %d (%s) no longer affine to cpu%d\n",
                                        task_pid_nr(p), p->comm, cpu);
                }
        }

        return dest_cpu;
}

/*
 * The caller (fork, wakeup) owns p->pi_lock, ->cpus_ptr is stable.
 */
static inline
int select_task_rq(struct task_struct *p, int cpu, int wake_flags)
{
        lockdep_assert_held(&p->pi_lock);

        if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p))
                cpu = p->sched_class->select_task_rq(p, cpu, wake_flags);
        else
                cpu = cpumask_any(p->cpus_ptr);

        /*
         * In order not to call set_task_cpu() on a blocking task we need
         * to rely on ttwu() to place the task on a valid ->cpus_ptr
         * CPU.
         *
         * Since this is common to all placement strategies, this lives here.
         *
         * [ this allows ->select_task() to simply return task_cpu(p) and
         *   not worry about this generic constraint ]
         */
        if (unlikely(!is_cpu_allowed(p, cpu)))
                cpu = select_fallback_rq(task_cpu(p), p);

        return cpu;
}

void sched_set_stop_task(int cpu, struct task_struct *stop)
{
        static struct lock_class_key stop_pi_lock;
        struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
        struct task_struct *old_stop = cpu_rq(cpu)->stop;

        if (stop) {
                /*
                 * Make it appear like a SCHED_FIFO task, its something
                 * userspace knows about and won't get confused about.
                 *
                 * Also, it will make PI more or less work without too
                 * much confusion -- but then, stop work should not
                 * rely on PI working anyway.
                 */
                sched_setscheduler_nocheck(stop, SCHED_FIFO, &param);

                stop->sched_class = &stop_sched_class;

                /*
                 * The PI code calls rt_mutex_setprio() with ->pi_lock held to
                 * adjust the effective priority of a task. As a result,
                 * rt_mutex_setprio() can trigger (RT) balancing operations,
                 * which can then trigger wakeups of the stop thread to push
                 * around the current task.
                 *
                 * The stop task itself will never be part of the PI-chain, it
                 * never blocks, therefore that ->pi_lock recursion is safe.
                 * Tell lockdep about this by placing the stop->pi_lock in its
                 * own class.
                 */
                lockdep_set_class(&stop->pi_lock, &stop_pi_lock);
        }

        cpu_rq(cpu)->stop = stop;

        if (old_stop) {
                /*
                 * Reset it back to a normal scheduling class so that
                 * it can die in pieces.
                 */
                old_stop->sched_class = &rt_sched_class;
        }
}

#else /* CONFIG_SMP */

static inline int __set_cpus_allowed_ptr(struct task_struct *p,
                                         const struct cpumask *new_mask,
                                         u32 flags)
{
        return set_cpus_allowed_ptr(p, new_mask);
}

static inline void migrate_disable_switch(struct rq *rq, struct task_struct *p) { }

static inline bool rq_has_pinned_tasks(struct rq *rq)
{
        return false;
}

#endif /* !CONFIG_SMP */

static void
ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq;

        if (!schedstat_enabled())
                return;

        rq = this_rq();

#ifdef CONFIG_SMP
        if (cpu == rq->cpu) {
                __schedstat_inc(rq->ttwu_local);
                __schedstat_inc(p->se.statistics.nr_wakeups_local);
        } else {
                struct sched_domain *sd;

                __schedstat_inc(p->se.statistics.nr_wakeups_remote);
                rcu_read_lock();
                for_each_domain(rq->cpu, sd) {
                        if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
                                __schedstat_inc(sd->ttwu_wake_remote);
                                break;
                        }
                }
                rcu_read_unlock();
        }

        if (wake_flags & WF_MIGRATED)
                __schedstat_inc(p->se.statistics.nr_wakeups_migrate);
#endif /* CONFIG_SMP */

        __schedstat_inc(rq->ttwu_count);
        __schedstat_inc(p->se.statistics.nr_wakeups);

        if (wake_flags & WF_SYNC)
                __schedstat_inc(p->se.statistics.nr_wakeups_sync);
}

/*
 * Mark the task runnable and perform wakeup-preemption.
 */
static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags,
                           struct rq_flags *rf)
{
        check_preempt_curr(rq, p, wake_flags);
        WRITE_ONCE(p->__state, TASK_RUNNING);
        trace_sched_wakeup(p);

#ifdef CONFIG_SMP
        if (p->sched_class->task_woken) {
                /*
                 * Our task @p is fully woken up and running; so it's safe to
                 * drop the rq->lock, hereafter rq is only used for statistics.
                 */
                rq_unpin_lock(rq, rf);
                p->sched_class->task_woken(rq, p);
                rq_repin_lock(rq, rf);
        }

        if (rq->idle_stamp) {
                u64 delta = rq_clock(rq) - rq->idle_stamp;
                u64 max = 2*rq->max_idle_balance_cost;

                update_avg(&rq->avg_idle, delta);

                if (rq->avg_idle > max)
                        rq->avg_idle = max;

                rq->wake_stamp = jiffies;
                rq->wake_avg_idle = rq->avg_idle / 2;

                rq->idle_stamp = 0;
        }
#endif
}

static void
ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
                 struct rq_flags *rf)
{
        int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK;

        lockdep_assert_rq_held(rq);

        if (p->sched_contributes_to_load)
                rq->nr_uninterruptible--;

#ifdef CONFIG_SMP
        if (wake_flags & WF_MIGRATED)
                en_flags |= ENQUEUE_MIGRATED;
        else
#endif
        if (p->in_iowait) {
                delayacct_blkio_end(p);
                atomic_dec(&task_rq(p)->nr_iowait);
        }

        activate_task(rq, p, en_flags);
        ttwu_do_wakeup(rq, p, wake_flags, rf);
}

/*
 * Consider @p being inside a wait loop:
 *
 *   for (;;) {
 *      set_current_state(TASK_UNINTERRUPTIBLE);
 *
 *      if (CONDITION)
 *         break;
 *
 *      schedule();
 *   }
 *   __set_current_state(TASK_RUNNING);
 *
 * between set_current_state() and schedule(). In this case @p is still
 * runnable, so all that needs doing is change p->state back to TASK_RUNNING in
 * an atomic manner.
 *
 * By taking task_rq(p)->lock we serialize against schedule(), if @p->on_rq
 * then schedule() must still happen and p->state can be changed to
 * TASK_RUNNING. Otherwise we lost the race, schedule() has happened, and we
 * need to do a full wakeup with enqueue.
 *
 * Returns: %true when the wakeup is done,
 *          %false otherwise.
 */
static int ttwu_runnable(struct task_struct *p, int wake_flags)
{
        struct rq_flags rf;
        struct rq *rq;
        int ret = 0;

        rq = __task_rq_lock(p, &rf);
        if (task_on_rq_queued(p)) {
                /* check_preempt_curr() may use rq clock */
                update_rq_clock(rq);
                ttwu_do_wakeup(rq, p, wake_flags, &rf);
                ret = 1;
        }
        __task_rq_unlock(rq, &rf);

        return ret;
}

#ifdef CONFIG_SMP
void sched_ttwu_pending(void *arg)
{
        struct llist_node *llist = arg;
        struct rq *rq = this_rq();
        struct task_struct *p, *t;
        struct rq_flags rf;

        if (!llist)
                return;

        /*
         * rq::ttwu_pending racy indication of out-standing wakeups.
         * Races such that false-negatives are possible, since they
         * are shorter lived that false-positives would be.
         */
        WRITE_ONCE(rq->ttwu_pending, 0);

        rq_lock_irqsave(rq, &rf);
        update_rq_clock(rq);

        llist_for_each_entry_safe(p, t, llist, wake_entry.llist) {
                if (WARN_ON_ONCE(p->on_cpu))
                        smp_cond_load_acquire(&p->on_cpu, !VAL);

                if (WARN_ON_ONCE(task_cpu(p) != cpu_of(rq)))
                        set_task_cpu(p, cpu_of(rq));

                ttwu_do_activate(rq, p, p->sched_remote_wakeup ? WF_MIGRATED : 0, &rf);
        }

        rq_unlock_irqrestore(rq, &rf);
}

void send_call_function_single_ipi(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (!set_nr_if_polling(rq->idle))
                arch_send_call_function_single_ipi(cpu);
        else
                trace_sched_wake_idle_without_ipi(cpu);
}

/*
 * Queue a task on the target CPUs wake_list and wake the CPU via IPI if
 * necessary. The wakee CPU on receipt of the IPI will queue the task
 * via sched_ttwu_wakeup() for activation so the wakee incurs the cost
 * of the wakeup instead of the waker.
 */
static void __ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq = cpu_rq(cpu);

        p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);

        WRITE_ONCE(rq->ttwu_pending, 1);
        __smp_call_single_queue(cpu, &p->wake_entry.llist);
}

void wake_up_if_idle(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        rcu_read_lock();

        if (!is_idle_task(rcu_dereference(rq->curr)))
                goto out;

        if (set_nr_if_polling(rq->idle)) {
                trace_sched_wake_idle_without_ipi(cpu);
        } else {
                rq_lock_irqsave(rq, &rf);
                if (is_idle_task(rq->curr))
                        smp_send_reschedule(cpu);
                /* Else CPU is not idle, do nothing here: */
                rq_unlock_irqrestore(rq, &rf);
        }

out:
        rcu_read_unlock();
}

bool cpus_share_cache(int this_cpu, int that_cpu)
{
        if (this_cpu == that_cpu)
                return true;

        return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
}

static inline bool ttwu_queue_cond(struct task_struct *p, int cpu)
{
        /*
         * Do not complicate things with the async wake_list while the CPU is
         * in hotplug state.
         */
        if (!cpu_active(cpu))
                return false;

        /* Ensure the task will still be allowed to run on the CPU. */
        if (!cpumask_test_cpu(cpu, p->cpus_ptr))
                return false;

        /*
         * If the CPU does not share cache, then queue the task on the
         * remote rqs wakelist to avoid accessing remote data.
         */
        if (!cpus_share_cache(smp_processor_id(), cpu))
                return true;

        if (cpu == smp_processor_id())
                return false;

        /*
         * If the wakee cpu is idle, or the task is descheduling and the
         * only running task on the CPU, then use the wakelist to offload
         * the task activation to the idle (or soon-to-be-idle) CPU as
         * the current CPU is likely busy. nr_running is checked to
         * avoid unnecessary task stacking.
         *
         * Note that we can only get here with (wakee) p->on_rq=0,
         * p->on_cpu can be whatever, we've done the dequeue, so
         * the wakee has been accounted out of ->nr_running.
         */
        if (!cpu_rq(cpu)->nr_running)
                return true;

        return false;
}

static bool ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
        if (sched_feat(TTWU_QUEUE) && ttwu_queue_cond(p, cpu)) {
                sched_clock_cpu(cpu); /* Sync clocks across CPUs */
                __ttwu_queue_wakelist(p, cpu, wake_flags);
                return true;
        }

        return false;
}

#else /* !CONFIG_SMP */

static inline bool ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags)
{
        return false;
}

#endif /* CONFIG_SMP */

static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        if (ttwu_queue_wakelist(p, cpu, wake_flags))
                return;

        rq_lock(rq, &rf);
        update_rq_clock(rq);
        ttwu_do_activate(rq, p, wake_flags, &rf);
        rq_unlock(rq, &rf);
}

/*
 * Invoked from try_to_wake_up() to check whether the task can be woken up.
 *
 * The caller holds p::pi_lock if p != current or has preemption
 * disabled when p == current.
 *
 * The rules of PREEMPT_RT saved_state:
 *
 *   The related locking code always holds p::pi_lock when updating
 *   p::saved_state, which means the code is fully serialized in both cases.
 *
 *   The lock wait and lock wakeups happen via TASK_RTLOCK_WAIT. No other
 *   bits set. This allows to distinguish all wakeup scenarios.
 */
static __always_inline
bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success)
{
        if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)) {
                WARN_ON_ONCE((state & TASK_RTLOCK_WAIT) &&
                             state != TASK_RTLOCK_WAIT);
        }

        if (READ_ONCE(p->__state) & state) {
                *success = 1;
                return true;
        }

#ifdef CONFIG_PREEMPT_RT
        /*
         * Saved state preserves the task state across blocking on
         * an RT lock.  If the state matches, set p::saved_state to
         * TASK_RUNNING, but do not wake the task because it waits
         * for a lock wakeup. Also indicate success because from
         * the regular waker's point of view this has succeeded.
         *
         * After acquiring the lock the task will restore p::__state
         * from p::saved_state which ensures that the regular
         * wakeup is not lost. The restore will also set
         * p::saved_state to TASK_RUNNING so any further tests will
         * not result in false positives vs. @success
         */
        if (p->saved_state & state) {
                p->saved_state = TASK_RUNNING;
                *success = 1;
        }
#endif
        return false;
}

/*
 * Notes on Program-Order guarantees on SMP systems.
 *
 *  MIGRATION
 *
 * The basic program-order guarantee on SMP systems is that when a task [t]
 * migrates, all its activity on its old CPU [c0] happens-before any subsequent
 * execution on its new CPU [c1].
 *
 * For migration (of runnable tasks) this is provided by the following means:
 *
 *  A) UNLOCK of the rq(c0)->lock scheduling out task t
 *  B) migration for t is required to synchronize *both* rq(c0)->lock and
 *     rq(c1)->lock (if not at the same time, then in that order).
 *  C) LOCK of the rq(c1)->lock scheduling in task
 *
 * Release/acquire chaining guarantees that B happens after A and C after B.
 * Note: the CPU doing B need not be c0 or c1
 *
 * Example:
 *
 *   CPU0            CPU1            CPU2
 *
 *   LOCK rq(0)->lock
 *   sched-out X
 *   sched-in Y
 *   UNLOCK rq(0)->lock
 *
 *                                   LOCK rq(0)->lock // orders against CPU0
 *                                   dequeue X
 *                                   UNLOCK rq(0)->lock
 *
 *                                   LOCK rq(1)->lock
 *                                   enqueue X
 *                                   UNLOCK rq(1)->lock
 *
 *                   LOCK rq(1)->lock // orders against CPU2
 *                   sched-out Z
 *                   sched-in X
 *                   UNLOCK rq(1)->lock
 *
 *
 *  BLOCKING -- aka. SLEEP + WAKEUP
 *
 * For blocking we (obviously) need to provide the same guarantee as for
 * migration. However the means are completely different as there is no lock
 * chain to provide order. Instead we do:
 *
 *   1) smp_store_release(X->on_cpu, 0)   -- finish_task()
 *   2) smp_cond_load_acquire(!X->on_cpu) -- try_to_wake_up()
 *
 * Example:
 *
 *   CPU0 (schedule)  CPU1 (try_to_wake_up) CPU2 (schedule)
 *
 *   LOCK rq(0)->lock LOCK X->pi_lock
 *   dequeue X
 *   sched-out X
 *   smp_store_release(X->on_cpu, 0);
 *
 *                    smp_cond_load_acquire(&X->on_cpu, !VAL);
 *                    X->state = WAKING
 *                    set_task_cpu(X,2)
 *
 *                    LOCK rq(2)->lock
 *                    enqueue X
 *                    X->state = RUNNING
 *                    UNLOCK rq(2)->lock
 *
 *                                          LOCK rq(2)->lock // orders against CPU1
 *                                          sched-out Z
 *                                          sched-in X
 *                                          UNLOCK rq(2)->lock
 *
 *                    UNLOCK X->pi_lock
 *   UNLOCK rq(0)->lock
 *
 *
 * However, for wakeups there is a second guarantee we must provide, namely we
 * must ensure that CONDITION=1 done by the caller can not be reordered with
 * accesses to the task state; see try_to_wake_up() and set_current_state().
 */

/**
 * try_to_wake_up - wake up a thread
 * @p: the thread to be awakened
 * @state: the mask of task states that can be woken
 * @wake_flags: wake modifier flags (WF_*)
 *
 * Conceptually does:
 *
 *   If (@state & @p->state) @p->state = TASK_RUNNING.
 *
 * If the task was not queued/runnable, also place it back on a runqueue.
 *
 * This function is atomic against schedule() which would dequeue the task.
 *
 * It issues a full memory barrier before accessing @p->state, see the comment
 * with set_current_state().
 *
 * Uses p->pi_lock to serialize against concurrent wake-ups.
 *
 * Relies on p->pi_lock stabilizing:
 *  - p->sched_class
 *  - p->cpus_ptr
 *  - p->sched_task_group
 * in order to do migration, see its use of select_task_rq()/set_task_cpu().
 *
 * Tries really hard to only take one task_rq(p)->lock for performance.
 * Takes rq->lock in:
 *  - ttwu_runnable()    -- old rq, unavoidable, see comment there;
 *  - ttwu_queue()       -- new rq, for enqueue of the task;
 *  - psi_ttwu_dequeue() -- much sadness :-( accounting will kill us.
 *
 * As a consequence we race really badly with just about everything. See the
 * many memory barriers and their comments for details.
 *
 * Return: %true if @p->state changes (an actual wakeup was done),
 *         %false otherwise.
 */
static int
try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
{
        unsigned long flags;
        int cpu, success = 0;

        preempt_disable();
        if (p == current) {
                /*
                 * We're waking current, this means 'p->on_rq' and 'task_cpu(p)
                 * == smp_processor_id()'. Together this means we can special
                 * case the whole 'p->on_rq && ttwu_runnable()' case below
                 * without taking any locks.
                 *
                 * In particular:
                 *  - we rely on Program-Order guarantees for all the ordering,
                 *  - we're serialized against set_special_state() by virtue of
                 *    it disabling IRQs (this allows not taking ->pi_lock).
                 */
                if (!ttwu_state_match(p, state, &success))
                        goto out;

                trace_sched_waking(p);
                WRITE_ONCE(p->__state, TASK_RUNNING);
                trace_sched_wakeup(p);
                goto out;
        }

        /*
         * If we are going to wake up a thread waiting for CONDITION we
         * need to ensure that CONDITION=1 done by the caller can not be
         * reordered with p->state check below. This pairs with smp_store_mb()
         * in set_current_state() that the waiting thread does.
         */
        raw_spin_lock_irqsave(&p->pi_lock, flags);
        smp_mb__after_spinlock();
        if (!ttwu_state_match(p, state, &success))
                goto unlock;

        trace_sched_waking(p);

        /*
         * Ensure we load p->on_rq _after_ p->state, otherwise it would
         * be possible to, falsely, observe p->on_rq == 0 and get stuck
         * in smp_cond_load_acquire() below.
         *
         * sched_ttwu_pending()                 try_to_wake_up()
         *   STORE p->on_rq = 1                   LOAD p->state
         *   UNLOCK rq->lock
         *
         * __schedule() (switch to task 'p')
         *   LOCK rq->lock                        smp_rmb();
         *   smp_mb__after_spinlock();
         *   UNLOCK rq->lock
         *
         * [task p]
         *   STORE p->state = UNINTERRUPTIBLE     LOAD p->on_rq
         *
         * Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
         * __schedule().  See the comment for smp_mb__after_spinlock().
         *
         * A similar smb_rmb() lives in try_invoke_on_locked_down_task().
         */
        smp_rmb();
        if (READ_ONCE(p->on_rq) && ttwu_runnable(p, wake_flags))
                goto unlock;

#ifdef CONFIG_SMP
        /*
         * Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be
         * possible to, falsely, observe p->on_cpu == 0.
         *
         * One must be running (->on_cpu == 1) in order to remove oneself
         * from the runqueue.
         *
         * __schedule() (switch to task 'p')    try_to_wake_up()
         *   STORE p->on_cpu = 1                  LOAD p->on_rq
         *   UNLOCK rq->lock
         *
         * __schedule() (put 'p' to sleep)
         *   LOCK rq->lock                        smp_rmb();
         *   smp_mb__after_spinlock();
         *   STORE p->on_rq = 0                   LOAD p->on_cpu
         *
         * Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
         * __schedule().  See the comment for smp_mb__after_spinlock().
         *
         * Form a control-dep-acquire with p->on_rq == 0 above, to ensure
         * schedule()'s deactivate_task() has 'happened' and p will no longer
         * care about it's own p->state. See the comment in __schedule().
         */
        smp_acquire__after_ctrl_dep();

        /*
         * We're doing the wakeup (@success == 1), they did a dequeue (p->on_rq
         * == 0), which means we need to do an enqueue, change p->state to
         * TASK_WAKING such that we can unlock p->pi_lock before doing the
         * enqueue, such as ttwu_queue_wakelist().
         */
        WRITE_ONCE(p->__state, TASK_WAKING);

        /*
         * If the owning (remote) CPU is still in the middle of schedule() with
         * this task as prev, considering queueing p on the remote CPUs wake_list
         * which potentially sends an IPI instead of spinning on p->on_cpu to
         * let the waker make forward progress. This is safe because IRQs are
         * disabled and the IPI will deliver after on_cpu is cleared.
         *
         * Ensure we load task_cpu(p) after p->on_cpu:
         *
         * set_task_cpu(p, cpu);
         *   STORE p->cpu = @cpu
         * __schedule() (switch to task 'p')
         *   LOCK rq->lock
         *   smp_mb__after_spin_lock()          smp_cond_load_acquire(&p->on_cpu)
         *   STORE p->on_cpu = 1                LOAD p->cpu
         *
         * to ensure we observe the correct CPU on which the task is currently
         * scheduling.
         */
        if (smp_load_acquire(&p->on_cpu) &&
            ttwu_queue_wakelist(p, task_cpu(p), wake_flags))
                goto unlock;

        /*
         * If the owning (remote) CPU is still in the middle of schedule() with
         * this task as prev, wait until it's done referencing the task.
         *
         * Pairs with the smp_store_release() in finish_task().
         *
         * This ensures that tasks getting woken will be fully ordered against
         * their previous state and preserve Program Order.
         */
        smp_cond_load_acquire(&p->on_cpu, !VAL);

        cpu = select_task_rq(p, p->wake_cpu, wake_flags | WF_TTWU);
        if (task_cpu(p) != cpu) {
                if (p->in_iowait) {
                        delayacct_blkio_end(p);
                        atomic_dec(&task_rq(p)->nr_iowait);
                }

                wake_flags |= WF_MIGRATED;
                psi_ttwu_dequeue(p);
                set_task_cpu(p, cpu);
        }
#else
        cpu = task_cpu(p);
#endif /* CONFIG_SMP */

        ttwu_queue(p, cpu, wake_flags);
unlock:
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
out:
        if (success)
                ttwu_stat(p, task_cpu(p), wake_flags);
        preempt_enable();

        return success;
}

/**
 * try_invoke_on_locked_down_task - Invoke a function on task in fixed state
 * @p: Process for which the function is to be invoked, can be @current.
 * @func: Function to invoke.
 * @arg: Argument to function.
 *
 * If the specified task can be quickly locked into a definite state
 * (either sleeping or on a given runqueue), arrange to keep it in that
 * state while invoking @func(@arg).  This function can use ->on_rq and
 * task_curr() to work out what the state is, if required.  Given that
 * @func can be invoked with a runqueue lock held, it had better be quite
 * lightweight.
 *
 * Returns:
 *      @false if the task slipped out from under the locks.
 *      @true if the task was locked onto a runqueue or is sleeping.
 *              However, @func can override this by returning @false.
 */
bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg)
{
        struct rq_flags rf;
        bool ret = false;
        struct rq *rq;

        raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
        if (p->on_rq) {
                rq = __task_rq_lock(p, &rf);
                if (task_rq(p) == rq)
                        ret = func(p, arg);
                rq_unlock(rq, &rf);
        } else {
                switch (READ_ONCE(p->__state)) {
                case TASK_RUNNING:
                case TASK_WAKING:
                        break;
                default:
                        smp_rmb(); // See smp_rmb() comment in try_to_wake_up().
                        if (!p->on_rq)
                                ret = func(p, arg);
                }
        }
        raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
        return ret;
}

/**
 * wake_up_process - Wake up a specific process
 * @p: The process to be woken up.
 *
 * Attempt to wake up the nominated process and move it to the set of runnable
 * processes.
 *
 * Return: 1 if the process was woken up, 0 if it was already running.
 *
 * This function executes a full memory barrier before accessing the task state.
 */
int wake_up_process(struct task_struct *p)
{
        return try_to_wake_up(p, TASK_NORMAL, 0);
}
EXPORT_SYMBOL(wake_up_process);

int wake_up_state(struct task_struct *p, unsigned int state)
{
        return try_to_wake_up(p, state, 0);
}

/*
 * Perform scheduler related setup for a newly forked process p.
 * p is forked by current.
 *
 * __sched_fork() is basic setup used by init_idle() too:
 */
static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
{
        p->on_rq                        = 0;

        p->se.on_rq                     = 0;
        p->se.exec_start                = 0;
        p->se.sum_exec_runtime          = 0;
        p->se.prev_sum_exec_runtime     = 0;
        p->se.nr_migrations             = 0;
        p->se.vruntime                  = 0;
        INIT_LIST_HEAD(&p->se.group_node);

#ifdef CONFIG_FAIR_GROUP_SCHED
        p->se.cfs_rq                    = NULL;
#endif

#ifdef CONFIG_SCHEDSTATS
        /* Even if schedstat is disabled, there should not be garbage */
        memset(&p->se.statistics, 0, sizeof(p->se.statistics));
#endif

        RB_CLEAR_NODE(&p->dl.rb_node);
        init_dl_task_timer(&p->dl);
        init_dl_inactive_task_timer(&p->dl);
        __dl_clear_params(p);

        INIT_LIST_HEAD(&p->rt.run_list);
        p->rt.timeout           = 0;
        p->rt.time_slice        = sched_rr_timeslice;
        p->rt.on_rq             = 0;
        p->rt.on_list           = 0;

#ifdef CONFIG_PREEMPT_NOTIFIERS
        INIT_HLIST_HEAD(&p->preempt_notifiers);
#endif

#ifdef CONFIG_COMPACTION
        p->capture_control = NULL;
#endif
        init_numa_balancing(clone_flags, p);
#ifdef CONFIG_SMP
        p->wake_entry.u_flags = CSD_TYPE_TTWU;
        p->migration_pending = NULL;
#endif
}

DEFINE_STATIC_KEY_FALSE(sched_numa_balancing);

#ifdef CONFIG_NUMA_BALANCING

void set_numabalancing_state(bool enabled)
{
        if (enabled)
                static_branch_enable(&sched_numa_balancing);
        else
                static_branch_disable(&sched_numa_balancing);
}

#ifdef CONFIG_PROC_SYSCTL
int sysctl_numa_balancing(struct ctl_table *table, int write,
                          void *buffer, size_t *lenp, loff_t *ppos)
{
        struct ctl_table t;
        int err;
        int state = static_branch_likely(&sched_numa_balancing);

        if (write && !capable(CAP_SYS_ADMIN))
                return -EPERM;

        t = *table;
        t.data = &state;
        err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
        if (err < 0)
                return err;
        if (write)
                set_numabalancing_state(state);
        return err;
}
#endif
#endif

#ifdef CONFIG_SCHEDSTATS

DEFINE_STATIC_KEY_FALSE(sched_schedstats);

static void set_schedstats(bool enabled)
{
        if (enabled)
                static_branch_enable(&sched_schedstats);
        else
                static_branch_disable(&sched_schedstats);
}

void force_schedstat_enabled(void)
{
        if (!schedstat_enabled()) {
                pr_info("kernel profiling enabled schedstats, disable via kernel.sched_schedstats.\n");
                static_branch_enable(&sched_schedstats);
        }
}

static int __init setup_schedstats(char *str)
{
        int ret = 0;
        if (!str)
                goto out;

        if (!strcmp(str, "enable")) {
                set_schedstats(true);
                ret = 1;
        } else if (!strcmp(str, "disable")) {
                set_schedstats(false);
                ret = 1;
        }
out:
        if (!ret)
                pr_warn("Unable to parse schedstats=\n");

        return ret;
}
__setup("schedstats=", setup_schedstats);

#ifdef CONFIG_PROC_SYSCTL
int sysctl_schedstats(struct ctl_table *table, int write, void *buffer,
                size_t *lenp, loff_t *ppos)
{
        struct ctl_table t;
        int err;
        int state = static_branch_likely(&sched_schedstats);

        if (write && !capable(CAP_SYS_ADMIN))
                return -EPERM;

        t = *table;
        t.data = &state;
        err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
        if (err < 0)
                return err;
        if (write)
                set_schedstats(state);
        return err;
}
#endif /* CONFIG_PROC_SYSCTL */
#endif /* CONFIG_SCHEDSTATS */

/*
 * fork()/clone()-time setup:
 */
int sched_fork(unsigned long clone_flags, struct task_struct *p)
{
        __sched_fork(clone_flags, p);
        /*
         * We mark the process as NEW here. This guarantees that
         * nobody will actually run it, and a signal or other external
         * event cannot wake it up and insert it on the runqueue either.
         */
        p->__state = TASK_NEW;

        /*
         * Make sure we do not leak PI boosting priority to the child.
         */
        p->prio = current->normal_prio;

        uclamp_fork(p);

        /*
         * Revert to default priority/policy on fork if requested.
         */
        if (unlikely(p->sched_reset_on_fork)) {
                if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
                        p->policy = SCHED_NORMAL;
                        p->static_prio = NICE_TO_PRIO(0);
                        p->rt_priority = 0;
                } else if (PRIO_TO_NICE(p->static_prio) < 0)
                        p->static_prio = NICE_TO_PRIO(0);

                p->prio = p->normal_prio = p->static_prio;
                set_load_weight(p, false);

                /*
                 * We don't need the reset flag anymore after the fork. It has
                 * fulfilled its duty:
                 */
                p->sched_reset_on_fork = 0;
        }

        if (dl_prio(p->prio))
                return -EAGAIN;
        else if (rt_prio(p->prio))
                p->sched_class = &rt_sched_class;
        else
                p->sched_class = &fair_sched_class;

        init_entity_runnable_average(&p->se);


#ifdef CONFIG_SCHED_INFO
        if (likely(sched_info_on()))
                memset(&p->sched_info, 0, sizeof(p->sched_info));
#endif
#if defined(CONFIG_SMP)
        p->on_cpu = 0;
#endif
        init_task_preempt_count(p);
#ifdef CONFIG_HAVE_PREEMPT_LAZY
        task_thread_info(p)->preempt_lazy_count = 0;
#endif
#ifdef CONFIG_SMP
        plist_node_init(&p->pushable_tasks, MAX_PRIO);
        RB_CLEAR_NODE(&p->pushable_dl_tasks);
#endif
        return 0;
}

void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)
{
        unsigned long flags;

        /*
         * Because we're not yet on the pid-hash, p->pi_lock isn't strictly
         * required yet, but lockdep gets upset if rules are violated.
         */
        raw_spin_lock_irqsave(&p->pi_lock, flags);
#ifdef CONFIG_CGROUP_SCHED
        if (1) {
                struct task_group *tg;
                tg = container_of(kargs->cset->subsys[cpu_cgrp_id],
                                  struct task_group, css);
                tg = autogroup_task_group(p, tg);
                p->sched_task_group = tg;
        }
#endif
        rseq_migrate(p);
        /*
         * We're setting the CPU for the first time, we don't migrate,
         * so use __set_task_cpu().
         */
        __set_task_cpu(p, smp_processor_id());
        if (p->sched_class->task_fork)
                p->sched_class->task_fork(p);
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
}

void sched_post_fork(struct task_struct *p)
{
        uclamp_post_fork(p);
}

unsigned long to_ratio(u64 period, u64 runtime)
{
        if (runtime == RUNTIME_INF)
                return BW_UNIT;

        /*
         * Doing this here saves a lot of checks in all
         * the calling paths, and returning zero seems
         * safe for them anyway.
         */
        if (period == 0)
                return 0;

        return div64_u64(runtime << BW_SHIFT, period);
}

/*
 * wake_up_new_task - wake up a newly created task for the first time.
 *
 * This function will do some initial scheduler statistics housekeeping
 * that must be done for every newly created context, then puts the task
 * on the runqueue and wakes it.
 */
void wake_up_new_task(struct task_struct *p)
{
        struct rq_flags rf;
        struct rq *rq;

        raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
        WRITE_ONCE(p->__state, TASK_RUNNING);
#ifdef CONFIG_SMP
        /*
         * Fork balancing, do it here and not earlier because:
         *  - cpus_ptr can change in the fork path
         *  - any previously selected CPU might disappear through hotplug
         *
         * Use __set_task_cpu() to avoid calling sched_class::migrate_task_rq,
         * as we're not fully set-up yet.
         */
        p->recent_used_cpu = task_cpu(p);
        rseq_migrate(p);
        __set_task_cpu(p, select_task_rq(p, task_cpu(p), WF_FORK));
#endif
        rq = __task_rq_lock(p, &rf);
        update_rq_clock(rq);
        post_init_entity_util_avg(p);

        activate_task(rq, p, ENQUEUE_NOCLOCK);
        trace_sched_wakeup_new(p);
        check_preempt_curr(rq, p, WF_FORK);
#ifdef CONFIG_SMP
        if (p->sched_class->task_woken) {
                /*
                 * Nothing relies on rq->lock after this, so it's fine to
                 * drop it.
                 */
                rq_unpin_lock(rq, &rf);
                p->sched_class->task_woken(rq, p);
                rq_repin_lock(rq, &rf);
        }
#endif
        task_rq_unlock(rq, p, &rf);
}

#ifdef CONFIG_PREEMPT_NOTIFIERS

static DEFINE_STATIC_KEY_FALSE(preempt_notifier_key);

void preempt_notifier_inc(void)
{
        static_branch_inc(&preempt_notifier_key);
}
EXPORT_SYMBOL_GPL(preempt_notifier_inc);

void preempt_notifier_dec(void)
{
        static_branch_dec(&preempt_notifier_key);
}
EXPORT_SYMBOL_GPL(preempt_notifier_dec);

/**
 * preempt_notifier_register - tell me when current is being preempted & rescheduled
 * @notifier: notifier struct to register
 */
void preempt_notifier_register(struct preempt_notifier *notifier)
{
        if (!static_branch_unlikely(&preempt_notifier_key))
                WARN(1, "registering preempt_notifier while notifiers disabled\n");

        hlist_add_head(&notifier->link, &current->preempt_notifiers);
}
EXPORT_SYMBOL_GPL(preempt_notifier_register);

/**
 * preempt_notifier_unregister - no longer interested in preemption notifications
 * @notifier: notifier struct to unregister
 *
 * This is *not* safe to call from within a preemption notifier.
 */
void preempt_notifier_unregister(struct preempt_notifier *notifier)
{
        hlist_del(&notifier->link);
}
EXPORT_SYMBOL_GPL(preempt_notifier_unregister);

static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
        struct preempt_notifier *notifier;

        hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
                notifier->ops->sched_in(notifier, raw_smp_processor_id());
}

static __always_inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
        if (static_branch_unlikely(&preempt_notifier_key))
                __fire_sched_in_preempt_notifiers(curr);
}

static void
__fire_sched_out_preempt_notifiers(struct task_struct *curr,
                                   struct task_struct *next)
{
        struct preempt_notifier *notifier;

        hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
                notifier->ops->sched_out(notifier, next);
}

static __always_inline void
fire_sched_out_preempt_notifiers(struct task_struct *curr,
                                 struct task_struct *next)
{
        if (static_branch_unlikely(&preempt_notifier_key))
                __fire_sched_out_preempt_notifiers(curr, next);
}

#else /* !CONFIG_PREEMPT_NOTIFIERS */

static inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
}

static inline void
fire_sched_out_preempt_notifiers(struct task_struct *curr,
                                 struct task_struct *next)
{
}

#endif /* CONFIG_PREEMPT_NOTIFIERS */

static inline void prepare_task(struct task_struct *next)
{
#ifdef CONFIG_SMP
        /*
         * Claim the task as running, we do this before switching to it
         * such that any running task will have this set.
         *
         * See the smp_load_acquire(&p->on_cpu) case in ttwu() and
         * its ordering comment.
         */
        WRITE_ONCE(next->on_cpu, 1);
#endif
}

static inline void finish_task(struct task_struct *prev)
{
#ifdef CONFIG_SMP
        /*
         * This must be the very last reference to @prev from this CPU. After
         * p->on_cpu is cleared, the task can be moved to a different CPU. We
         * must ensure this doesn't happen until the switch is completely
         * finished.
         *
         * In particular, the load of prev->state in finish_task_switch() must
         * happen before this.
         *
         * Pairs with the smp_cond_load_acquire() in try_to_wake_up().
         */
        smp_store_release(&prev->on_cpu, 0);
#endif
}

#ifdef CONFIG_SMP

static void do_balance_callbacks(struct rq *rq, struct callback_head *head)
{
        void (*func)(struct rq *rq);
        struct callback_head *next;

        lockdep_assert_rq_held(rq);

        while (head) {
                func = (void (*)(struct rq *))head->func;
                next = head->next;
                head->next = NULL;
                head = next;

                func(rq);
        }
}

static void balance_push(struct rq *rq);

/*
 * balance_push_callback is a right abuse of the callback interface and plays
 * by significantly different rules.
 *
 * Where the normal balance_callback's purpose is to be ran in the same context
 * that queued it (only later, when it's safe to drop rq->lock again),
 * balance_push_callback is specifically targeted at __schedule().
 *
 * This abuse is tolerated because it places all the unlikely/odd cases behind
 * a single test, namely: rq->balance_callback == NULL.
 */
struct callback_head balance_push_callback = {
        .next = NULL,
        .func = (void (*)(struct callback_head *))balance_push,
};

static inline struct callback_head *
__splice_balance_callbacks(struct rq *rq, bool split)
{
        struct callback_head *head = rq->balance_callback;

        if (likely(!head))
                return NULL;

        lockdep_assert_rq_held(rq);
        /*
         * Must not take balance_push_callback off the list when
         * splice_balance_callbacks() and balance_callbacks() are not
         * in the same rq->lock section.
         *
         * In that case it would be possible for __schedule() to interleave
         * and observe the list empty.
         */
        if (split && head == &balance_push_callback)
                head = NULL;
        else
                rq->balance_callback = NULL;

        return head;
}

static inline struct callback_head *splice_balance_callbacks(struct rq *rq)
{
        return __splice_balance_callbacks(rq, true);
}

static void __balance_callbacks(struct rq *rq)
{
        do_balance_callbacks(rq, __splice_balance_callbacks(rq, false));
}

static inline void balance_callbacks(struct rq *rq, struct callback_head *head)
{
        unsigned long flags;

        if (unlikely(head)) {
                raw_spin_rq_lock_irqsave(rq, flags);
                do_balance_callbacks(rq, head);
                raw_spin_rq_unlock_irqrestore(rq, flags);
        }
}

#else

static inline void __balance_callbacks(struct rq *rq)
{
}

static inline struct callback_head *splice_balance_callbacks(struct rq *rq)
{
        return NULL;
}

static inline void balance_callbacks(struct rq *rq, struct callback_head *head)
{
}

#endif

static inline void
prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
{
        /*
         * Since the runqueue lock will be released by the next
         * task (which is an invalid locking op but in the case
         * of the scheduler it's an obvious special-case), so we
         * do an early lockdep release here:
         */
        rq_unpin_lock(rq, rf);
        spin_release(&__rq_lockp(rq)->dep_map, _THIS_IP_);
#ifdef CONFIG_DEBUG_SPINLOCK
        /* this is a valid case when another task releases the spinlock */
        rq_lockp(rq)->owner = next;
#endif
}

static inline void finish_lock_switch(struct rq *rq)
{
        /*
         * If we are tracking spinlock dependencies then we have to
         * fix up the runqueue lock - which gets 'carried over' from
         * prev into current:
         */
        spin_acquire(&__rq_lockp(rq)->dep_map, 0, 0, _THIS_IP_);
        __balance_callbacks(rq);
        raw_spin_rq_unlock_irq(rq);
}

/*
 * NOP if the arch has not defined these:
 */

#ifndef prepare_arch_switch
# define prepare_arch_switch(next)      do { } while (0)
#endif

#ifndef finish_arch_post_lock_switch
# define finish_arch_post_lock_switch() do { } while (0)
#endif

static inline void kmap_local_sched_out(void)
{
#ifdef CONFIG_KMAP_LOCAL
        if (unlikely(current->kmap_ctrl.idx))
                __kmap_local_sched_out();
#endif
}

static inline void kmap_local_sched_in(void)
{
#ifdef CONFIG_KMAP_LOCAL
        if (unlikely(current->kmap_ctrl.idx))
                __kmap_local_sched_in();
#endif
}

/**
 * prepare_task_switch - prepare to switch tasks
 * @rq: the runqueue preparing to switch
 * @prev: the current task that is being switched out
 * @next: the task we are going to switch to.
 *
 * This is called with the rq lock held and interrupts off. It must
 * be paired with a subsequent finish_task_switch after the context
 * switch.
 *
 * prepare_task_switch sets up locking and calls architecture specific
 * hooks.
 */
static inline void
prepare_task_switch(struct rq *rq, struct task_struct *prev,
                    struct task_struct *next)
{
        kcov_prepare_switch(prev);
        sched_info_switch(rq, prev, next);
        perf_event_task_sched_out(prev, next);
        rseq_preempt(prev);
        fire_sched_out_preempt_notifiers(prev, next);
        kmap_local_sched_out();
        prepare_task(next);
        prepare_arch_switch(next);
}

/**
 * finish_task_switch - clean up after a task-switch
 * @prev: the thread we just switched away from.
 *
 * finish_task_switch must be called after the context switch, paired
 * with a prepare_task_switch call before the context switch.
 * finish_task_switch will reconcile locking set up by prepare_task_switch,
 * and do any other architecture-specific cleanup actions.
 *
 * Note that we may have delayed dropping an mm in context_switch(). If
 * so, we finish that here outside of the runqueue lock. (Doing it
 * with the lock held can cause deadlocks; see schedule() for
 * details.)
 *
 * The context switch have flipped the stack from under us and restored the
 * local variables which were saved when this task called schedule() in the
 * past. prev == current is still correct but we need to recalculate this_rq
 * because prev may have moved to another CPU.
 */
static struct rq *finish_task_switch(struct task_struct *prev)
        __releases(rq->lock)
{
        struct rq *rq = this_rq();
        struct mm_struct *mm = rq->prev_mm;
        long prev_state;

        /*
         * The previous task will have left us with a preempt_count of 2
         * because it left us after:
         *
         *      schedule()
         *        preempt_disable();                    // 1
         *        __schedule()
         *          raw_spin_lock_irq(&rq->lock)        // 2
         *
         * Also, see FORK_PREEMPT_COUNT.
         */
        if (WARN_ONCE(preempt_count() != 2*PREEMPT_DISABLE_OFFSET,
                      "corrupted preempt_count: %s/%d/0x%x\n",
                      current->comm, current->pid, preempt_count()))
                preempt_count_set(FORK_PREEMPT_COUNT);

        rq->prev_mm = NULL;

        /*
         * A task struct has one reference for the use as "current".
         * If a task dies, then it sets TASK_DEAD in tsk->state and calls
         * schedule one last time. The schedule call will never return, and
         * the scheduled task must drop that reference.
         *
         * We must observe prev->state before clearing prev->on_cpu (in
         * finish_task), otherwise a concurrent wakeup can get prev
         * running on another CPU and we could rave with its RUNNING -> DEAD
         * transition, resulting in a double drop.
         */
        prev_state = READ_ONCE(prev->__state);
        vtime_task_switch(prev);
        perf_event_task_sched_in(prev, current);
        finish_task(prev);
        tick_nohz_task_switch();
        finish_lock_switch(rq);
        finish_arch_post_lock_switch();
        kcov_finish_switch(current);
        /*
         * kmap_local_sched_out() is invoked with rq::lock held and
         * interrupts disabled. There is no requirement for that, but the
         * sched out code does not have an interrupt enabled section.
         * Restoring the maps on sched in does not require interrupts being
         * disabled either.
         */
        kmap_local_sched_in();

        fire_sched_in_preempt_notifiers(current);
        /*
         * When switching through a kernel thread, the loop in
         * membarrier_{private,global}_expedited() may have observed that
         * kernel thread and not issued an IPI. It is therefore possible to
         * schedule between user->kernel->user threads without passing though
         * switch_mm(). Membarrier requires a barrier after storing to
         * rq->curr, before returning to userspace, so provide them here:
         *
         * - a full memory barrier for {PRIVATE,GLOBAL}_EXPEDITED, implicitly
         *   provided by mmdrop(),
         * - a sync_core for SYNC_CORE.
         */
        if (mm) {
                membarrier_mm_sync_core_before_usermode(mm);
                mmdrop_sched(mm);
        }
        if (unlikely(prev_state == TASK_DEAD)) {
                if (prev->sched_class->task_dead)
                        prev->sched_class->task_dead(prev);

                /*
                 * Release VMAP'ed task stack immediate for reuse. On RT
                 * enabled kernels this is delayed for latency reasons.
                 */
                if (!IS_ENABLED(CONFIG_PREEMPT_RT))
                        put_task_stack(prev);

                put_task_struct_rcu_user(prev);
        }

        return rq;
}

/**
 * schedule_tail - first thing a freshly forked thread must call.
 * @prev: the thread we just switched away from.
 */
asmlinkage __visible void schedule_tail(struct task_struct *prev)
        __releases(rq->lock)
{
        /*
         * New tasks start with FORK_PREEMPT_COUNT, see there and
         * finish_task_switch() for details.
         *
         * finish_task_switch() will drop rq->lock() and lower preempt_count
         * and the preempt_enable() will end up enabling preemption (on
         * PREEMPT_COUNT kernels).
         */

        finish_task_switch(prev);
        preempt_enable();

        if (current->set_child_tid)
                put_user(task_pid_vnr(current), current->set_child_tid);

        calculate_sigpending();
}

/*
 * context_switch - switch to the new MM and the new thread's register state.
 */
static __always_inline struct rq *
context_switch(struct rq *rq, struct task_struct *prev,
               struct task_struct *next, struct rq_flags *rf)
{
        prepare_task_switch(rq, prev, next);

        /*
         * For paravirt, this is coupled with an exit in switch_to to
         * combine the page table reload and the switch backend into
         * one hypercall.
         */
        arch_start_context_switch(prev);

        /*
         * kernel -> kernel   lazy + transfer active
         *   user -> kernel   lazy + mmgrab() active
         *
         * kernel ->   user   switch + mmdrop() active
         *   user ->   user   switch
         */
        if (!next->mm) {                                // to kernel
                enter_lazy_tlb(prev->active_mm, next);

                next->active_mm = prev->active_mm;
                if (prev->mm)                           // from user
                        mmgrab(prev->active_mm);
                else
                        prev->active_mm = NULL;
        } else {                                        // to user
                membarrier_switch_mm(rq, prev->active_mm, next->mm);
                /*
                 * sys_membarrier() requires an smp_mb() between setting
                 * rq->curr / membarrier_switch_mm() and returning to userspace.
                 *
                 * The below provides this either through switch_mm(), or in
                 * case 'prev->active_mm == next->mm' through
                 * finish_task_switch()'s mmdrop().
                 */
                switch_mm_irqs_off(prev->active_mm, next->mm, next);

                if (!prev->mm) {                        // from kernel
                        /* will mmdrop() in finish_task_switch(). */
                        rq->prev_mm = prev->active_mm;
                        prev->active_mm = NULL;
                }
        }

        rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);

        prepare_lock_switch(rq, next, rf);

        /* Here we just switch the register state and the stack. */
        switch_to(prev, next, prev);
        barrier();

        return finish_task_switch(prev);
}

/*
 * nr_running and nr_context_switches:
 *
 * externally visible scheduler statistics: current number of runnable
 * threads, total number of context switches performed since bootup.
 */
unsigned int nr_running(void)
{
        unsigned int i, sum = 0;

        for_each_online_cpu(i)
                sum += cpu_rq(i)->nr_running;

        return sum;
}

/*
 * Check if only the current task is running on the CPU.
 *
 * Caution: this function does not check that the caller has disabled
 * preemption, thus the result might have a time-of-check-to-time-of-use
 * race.  The caller is responsible to use it correctly, for example:
 *
 * - from a non-preemptible section (of course)
 *
 * - from a thread that is bound to a single CPU
 *
 * - in a loop with very short iterations (e.g. a polling loop)
 */
bool single_task_running(void)
{
        return raw_rq()->nr_running == 1;
}
EXPORT_SYMBOL(single_task_running);

unsigned long long nr_context_switches(void)
{
        int i;
        unsigned long long sum = 0;

        for_each_possible_cpu(i)
                sum += cpu_rq(i)->nr_switches;

        return sum;
}

/*
 * Consumers of these two interfaces, like for example the cpuidle menu
 * governor, are using nonsensical data. Preferring shallow idle state selection
 * for a CPU that has IO-wait which might not even end up running the task when
 * it does become runnable.
 */

unsigned int nr_iowait_cpu(int cpu)
{
        return atomic_read(&cpu_rq(cpu)->nr_iowait);
}

/*
 * IO-wait accounting, and how it's mostly bollocks (on SMP).
 *
 * The idea behind IO-wait account is to account the idle time that we could
 * have spend running if it were not for IO. That is, if we were to improve the
 * storage performance, we'd have a proportional reduction in IO-wait time.
 *
 * This all works nicely on UP, where, when a task blocks on IO, we account
 * idle time as IO-wait, because if the storage were faster, it could've been
 * running and we'd not be idle.
 *
 * This has been extended to SMP, by doing the same for each CPU. This however
 * is broken.
 *
 * Imagine for instance the case where two tasks block on one CPU, only the one
 * CPU will have IO-wait accounted, while the other has regular idle. Even
 * though, if the storage were faster, both could've ran at the same time,
 * utilising both CPUs.
 *
 * This means, that when looking globally, the current IO-wait accounting on
 * SMP is a lower bound, by reason of under accounting.
 *
 * Worse, since the numbers are provided per CPU, they are sometimes
 * interpreted per CPU, and that is nonsensical. A blocked task isn't strictly
 * associated with any one particular CPU, it can wake to another CPU than it
 * blocked on. This means the per CPU IO-wait number is meaningless.
 *
 * Task CPU affinities can make all that even more 'interesting'.
 */

unsigned int nr_iowait(void)
{
        unsigned int i, sum = 0;

        for_each_possible_cpu(i)
                sum += nr_iowait_cpu(i);

        return sum;
}

#ifdef CONFIG_SMP

/*
 * sched_exec - execve() is a valuable balancing opportunity, because at
 * this point the task has the smallest effective memory and cache footprint.
 */
void sched_exec(void)
{
        struct task_struct *p = current;
        unsigned long flags;
        int dest_cpu;

        raw_spin_lock_irqsave(&p->pi_lock, flags);
        dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), WF_EXEC);
        if (dest_cpu == smp_processor_id())
                goto unlock;

        if (likely(cpu_active(dest_cpu))) {
                struct migration_arg arg = { p, dest_cpu };

                raw_spin_unlock_irqrestore(&p->pi_lock, flags);
                stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
                return;
        }
unlock:
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
}

#endif

DEFINE_PER_CPU(struct kernel_stat, kstat);
DEFINE_PER_CPU(struct kernel_cpustat, kernel_cpustat);

EXPORT_PER_CPU_SYMBOL(kstat);
EXPORT_PER_CPU_SYMBOL(kernel_cpustat);

/*
 * The function fair_sched_class.update_curr accesses the struct curr
 * and its field curr->exec_start; when called from task_sched_runtime(),
 * we observe a high rate of cache misses in practice.
 * Prefetching this data results in improved performance.
 */
static inline void prefetch_curr_exec_start(struct task_struct *p)
{
#ifdef CONFIG_FAIR_GROUP_SCHED
        struct sched_entity *curr = (&p->se)->cfs_rq->curr;
#else
        struct sched_entity *curr = (&task_rq(p)->cfs)->curr;
#endif
        prefetch(curr);
        prefetch(&curr->exec_start);
}

/*
 * Return accounted runtime for the task.
 * In case the task is currently running, return the runtime plus current's
 * pending runtime that have not been accounted yet.
 */
unsigned long long task_sched_runtime(struct task_struct *p)
{
        struct rq_flags rf;
        struct rq *rq;
        u64 ns;

#if defined(CONFIG_64BIT) && defined(CONFIG_SMP)
        /*
         * 64-bit doesn't need locks to atomically read a 64-bit value.
         * So we have a optimization chance when the task's delta_exec is 0.
         * Reading ->on_cpu is racy, but this is ok.
         *
         * If we race with it leaving CPU, we'll take a lock. So we're correct.
         * If we race with it entering CPU, unaccounted time is 0. This is
         * indistinguishable from the read occurring a few cycles earlier.
         * If we see ->on_cpu without ->on_rq, the task is leaving, and has
         * been accounted, so we're correct here as well.
         */
        if (!p->on_cpu || !task_on_rq_queued(p))
                return p->se.sum_exec_runtime;
#endif

        rq = task_rq_lock(p, &rf);
        /*
         * Must be ->curr _and_ ->on_rq.  If dequeued, we would
         * project cycles that may never be accounted to this
         * thread, breaking clock_gettime().
         */
        if (task_current(rq, p) && task_on_rq_queued(p)) {
                prefetch_curr_exec_start(p);
                update_rq_clock(rq);
                p->sched_class->update_curr(rq);
        }
        ns = p->se.sum_exec_runtime;
        task_rq_unlock(rq, p, &rf);

        return ns;
}

#ifdef CONFIG_SCHED_DEBUG
static u64 cpu_resched_latency(struct rq *rq)
{
        int latency_warn_ms = READ_ONCE(sysctl_resched_latency_warn_ms);
        u64 resched_latency, now = rq_clock(rq);
        static bool warned_once;

        if (sysctl_resched_latency_warn_once && warned_once)
                return 0;

        if (!need_resched() || !latency_warn_ms)
                return 0;

        if (system_state == SYSTEM_BOOTING)
                return 0;

        if (!rq->last_seen_need_resched_ns) {
                rq->last_seen_need_resched_ns = now;
                rq->ticks_without_resched = 0;
                return 0;
        }

        rq->ticks_without_resched++;
        resched_latency = now - rq->last_seen_need_resched_ns;
        if (resched_latency <= latency_warn_ms * NSEC_PER_MSEC)
                return 0;

        warned_once = true;

        return resched_latency;
}

static int __init setup_resched_latency_warn_ms(char *str)
{
        long val;

        if ((kstrtol(str, 0, &val))) {
                pr_warn("Unable to set resched_latency_warn_ms\n");
                return 1;
        }

        sysctl_resched_latency_warn_ms = val;
        return 1;
}
__setup("resched_latency_warn_ms=", setup_resched_latency_warn_ms);
#else
static inline u64 cpu_resched_latency(struct rq *rq) { return 0; }
#endif /* CONFIG_SCHED_DEBUG */

/*
 * This function gets called by the timer code, with HZ frequency.
 * We call it with interrupts disabled.
 */
void scheduler_tick(void)
{
        int cpu = smp_processor_id();
        struct rq *rq = cpu_rq(cpu);
        struct task_struct *curr = rq->curr;
        struct rq_flags rf;
        unsigned long thermal_pressure;
        u64 resched_latency;

        arch_scale_freq_tick();
        sched_clock_tick();

        rq_lock(rq, &rf);

        update_rq_clock(rq);
        thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
        update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
        curr->sched_class->task_tick(rq, curr, 0);
        if (sched_feat(LATENCY_WARN))
                resched_latency = cpu_resched_latency(rq);
        calc_global_load_tick(rq);

        rq_unlock(rq, &rf);

        if (sched_feat(LATENCY_WARN) && resched_latency)
                resched_latency_warn(cpu, resched_latency);

        perf_event_task_tick();

#ifdef CONFIG_SMP
        rq->idle_balance = idle_cpu(cpu);
        trigger_load_balance(rq);
#endif
}

#ifdef CONFIG_NO_HZ_FULL

struct tick_work {
        int                     cpu;
        atomic_t                state;
        struct delayed_work     work;
};
/* Values for ->state, see diagram below. */
#define TICK_SCHED_REMOTE_OFFLINE       0
#define TICK_SCHED_REMOTE_OFFLINING     1
#define TICK_SCHED_REMOTE_RUNNING       2

/*
 * State diagram for ->state:
 *
 *
 *          TICK_SCHED_REMOTE_OFFLINE
 *                    |   ^
 *                    |   |
 *                    |   | sched_tick_remote()
 *                    |   |
 *                    |   |
 *                    +--TICK_SCHED_REMOTE_OFFLINING
 *                    |   ^
 *                    |   |
 * sched_tick_start() |   | sched_tick_stop()
 *                    |   |
 *                    V   |
 *          TICK_SCHED_REMOTE_RUNNING
 *
 *
 * Other transitions get WARN_ON_ONCE(), except that sched_tick_remote()
 * and sched_tick_start() are happy to leave the state in RUNNING.
 */

static struct tick_work __percpu *tick_work_cpu;

static void sched_tick_remote(struct work_struct *work)
{
        struct delayed_work *dwork = to_delayed_work(work);
        struct tick_work *twork = container_of(dwork, struct tick_work, work);
        int cpu = twork->cpu;
        struct rq *rq = cpu_rq(cpu);
        struct task_struct *curr;
        struct rq_flags rf;
        u64 delta;
        int os;

        /*
         * Handle the tick only if it appears the remote CPU is running in full
         * dynticks mode. The check is racy by nature, but missing a tick or
         * having one too much is no big deal because the scheduler tick updates
         * statistics and checks timeslices in a time-independent way, regardless
         * of when exactly it is running.
         */
        if (!tick_nohz_tick_stopped_cpu(cpu))
                goto out_requeue;

        rq_lock_irq(rq, &rf);
        curr = rq->curr;
        if (cpu_is_offline(cpu))
                goto out_unlock;

        update_rq_clock(rq);

        if (!is_idle_task(curr)) {
                /*
                 * Make sure the next tick runs within a reasonable
                 * amount of time.
                 */
                delta = rq_clock_task(rq) - curr->se.exec_start;
                WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
        }
        curr->sched_class->task_tick(rq, curr, 0);

        calc_load_nohz_remote(rq);
out_unlock:
        rq_unlock_irq(rq, &rf);
out_requeue:

        /*
         * Run the remote tick once per second (1Hz). This arbitrary
         * frequency is large enough to avoid overload but short enough
         * to keep scheduler internal stats reasonably up to date.  But
         * first update state to reflect hotplug activity if required.
         */
        os = atomic_fetch_add_unless(&twork->state, -1, TICK_SCHED_REMOTE_RUNNING);
        WARN_ON_ONCE(os == TICK_SCHED_REMOTE_OFFLINE);
        if (os == TICK_SCHED_REMOTE_RUNNING)
                queue_delayed_work(system_unbound_wq, dwork, HZ);
}

static void sched_tick_start(int cpu)
{
        int os;
        struct tick_work *twork;

        if (housekeeping_cpu(cpu, HK_FLAG_TICK))
                return;

        WARN_ON_ONCE(!tick_work_cpu);

        twork = per_cpu_ptr(tick_work_cpu, cpu);
        os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_RUNNING);
        WARN_ON_ONCE(os == TICK_SCHED_REMOTE_RUNNING);
        if (os == TICK_SCHED_REMOTE_OFFLINE) {
                twork->cpu = cpu;
                INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
                queue_delayed_work(system_unbound_wq, &twork->work, HZ);
        }
}

#ifdef CONFIG_HOTPLUG_CPU
static void sched_tick_stop(int cpu)
{
        struct tick_work *twork;
        int os;

        if (housekeeping_cpu(cpu, HK_FLAG_TICK))
                return;

        WARN_ON_ONCE(!tick_work_cpu);

        twork = per_cpu_ptr(tick_work_cpu, cpu);
        /* There cannot be competing actions, but don't rely on stop-machine. */
        os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_OFFLINING);
        WARN_ON_ONCE(os != TICK_SCHED_REMOTE_RUNNING);
        /* Don't cancel, as this would mess up the state machine. */
}
#endif /* CONFIG_HOTPLUG_CPU */

int __init sched_tick_offload_init(void)
{
        tick_work_cpu = alloc_percpu(struct tick_work);
        BUG_ON(!tick_work_cpu);
        return 0;
}

#else /* !CONFIG_NO_HZ_FULL */
static inline void sched_tick_start(int cpu) { }
static inline void sched_tick_stop(int cpu) { }
#endif

#if defined(CONFIG_PREEMPTION) && (defined(CONFIG_DEBUG_PREEMPT) || \
                                defined(CONFIG_TRACE_PREEMPT_TOGGLE))
/*
 * If the value passed in is equal to the current preempt count
 * then we just disabled preemption. Start timing the latency.
 */
static inline void preempt_latency_start(int val)
{
        if (preempt_count() == val) {
                unsigned long ip = get_lock_parent_ip();
#ifdef CONFIG_DEBUG_PREEMPT
                current->preempt_disable_ip = ip;
#endif
                trace_preempt_off(CALLER_ADDR0, ip);
        }
}

void preempt_count_add(int val)
{
#ifdef CONFIG_DEBUG_PREEMPT
        /*
         * Underflow?
         */
        if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
                return;
#endif
        __preempt_count_add(val);
#ifdef CONFIG_DEBUG_PREEMPT
        /*
         * Spinlock count overflowing soon?
         */
        DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=
                                PREEMPT_MASK - 10);
#endif
        preempt_latency_start(val);
}
EXPORT_SYMBOL(preempt_count_add);
NOKPROBE_SYMBOL(preempt_count_add);

/*
 * If the value passed in equals to the current preempt count
 * then we just enabled preemption. Stop timing the latency.
 */
static inline void preempt_latency_stop(int val)
{
        if (preempt_count() == val)
                trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
}

void preempt_count_sub(int val)
{
#ifdef CONFIG_DEBUG_PREEMPT
        /*
         * Underflow?
         */
        if (DEBUG_LOCKS_WARN_ON(val > preempt_count()))
                return;
        /*
         * Is the spinlock portion underflowing?
         */
        if (DEBUG_LOCKS_WARN_ON((val < PREEMPT_MASK) &&
                        !(preempt_count() & PREEMPT_MASK)))
                return;
#endif

        preempt_latency_stop(val);
        __preempt_count_sub(val);
}
EXPORT_SYMBOL(preempt_count_sub);
NOKPROBE_SYMBOL(preempt_count_sub);

#else
static inline void preempt_latency_start(int val) { }
static inline void preempt_latency_stop(int val) { }
#endif

static inline unsigned long get_preempt_disable_ip(struct task_struct *p)
{
#ifdef CONFIG_DEBUG_PREEMPT
        return p->preempt_disable_ip;
#else
        return 0;
#endif
}

/*
 * Print scheduling while atomic bug:
 */
static noinline void __schedule_bug(struct task_struct *prev)
{
        /* Save this before calling printk(), since that will clobber it */
        unsigned long preempt_disable_ip = get_preempt_disable_ip(current);

        if (oops_in_progress)
                return;

        printk(KERN_ERR "BUG: scheduling while atomic: %s/%d/0x%08x\n",
                prev->comm, prev->pid, preempt_count());

        debug_show_held_locks(prev);
        print_modules();
        if (irqs_disabled())
                print_irqtrace_events(prev);
        if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)
            && in_atomic_preempt_off()) {
                pr_err("Preemption disabled at:");
                print_ip_sym(KERN_ERR, preempt_disable_ip);
        }
        check_panic_on_warn("scheduling while atomic");

        dump_stack();
        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}

/*
 * Various schedule()-time debugging checks and statistics:
 */
static inline void schedule_debug(struct task_struct *prev, bool preempt)
{
#ifdef CONFIG_SCHED_STACK_END_CHECK
        if (task_stack_end_corrupted(prev))
                panic("corrupted stack end detected inside scheduler\n");

        if (task_scs_end_corrupted(prev))
                panic("corrupted shadow stack detected inside scheduler\n");
#endif

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
        if (!preempt && READ_ONCE(prev->__state) && prev->non_block_count) {
                printk(KERN_ERR "BUG: scheduling in a non-blocking section: %s/%d/%i\n",
                        prev->comm, prev->pid, prev->non_block_count);
                dump_stack();
                add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
        }
#endif

        if (unlikely(in_atomic_preempt_off())) {
                __schedule_bug(prev);
                preempt_count_set(PREEMPT_DISABLED);
        }
        rcu_sleep_check();
        SCHED_WARN_ON(ct_state() == CONTEXT_USER);

        profile_hit(SCHED_PROFILING, __builtin_return_address(0));

        schedstat_inc(this_rq()->sched_count);
}

static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
                                  struct rq_flags *rf)
{
#ifdef CONFIG_SMP
        const struct sched_class *class;
        /*
         * We must do the balancing pass before put_prev_task(), such
         * that when we release the rq->lock the task is in the same
         * state as before we took rq->lock.
         *
         * We can terminate the balance pass as soon as we know there is
         * a runnable task of @class priority or higher.
         */
        for_class_range(class, prev->sched_class, &idle_sched_class) {
                if (class->balance(rq, prev, rf))
                        break;
        }
#endif

        put_prev_task(rq, prev);
}

/*
 * Pick up the highest-prio task:
 */
static inline struct task_struct *
__pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
        const struct sched_class *class;
        struct task_struct *p;

        /*
         * Optimization: we know that if all tasks are in the fair class we can
         * call that function directly, but only if the @prev task wasn't of a
         * higher scheduling class, because otherwise those lose the
         * opportunity to pull in more work from other CPUs.
         */
        if (likely(prev->sched_class <= &fair_sched_class &&
                   rq->nr_running == rq->cfs.h_nr_running)) {

                p = pick_next_task_fair(rq, prev, rf);
                if (unlikely(p == RETRY_TASK))
                        goto restart;

                /* Assume the next prioritized class is idle_sched_class */
                if (!p) {
                        put_prev_task(rq, prev);
                        p = pick_next_task_idle(rq);
                }

                return p;
        }

restart:
        put_prev_task_balance(rq, prev, rf);

        for_each_class(class) {
                p = class->pick_next_task(rq);
                if (p)
                        return p;
        }

        /* The idle class should always have a runnable task: */
        BUG();
}

#ifdef CONFIG_SCHED_CORE
static inline bool is_task_rq_idle(struct task_struct *t)
{
        return (task_rq(t)->idle == t);
}

static inline bool cookie_equals(struct task_struct *a, unsigned long cookie)
{
        return is_task_rq_idle(a) || (a->core_cookie == cookie);
}

static inline bool cookie_match(struct task_struct *a, struct task_struct *b)
{
        if (is_task_rq_idle(a) || is_task_rq_idle(b))
                return true;

        return a->core_cookie == b->core_cookie;
}

// XXX fairness/fwd progress conditions
/*
 * Returns
 * - NULL if there is no runnable task for this class.
 * - the highest priority task for this runqueue if it matches
 *   rq->core->core_cookie or its priority is greater than max.
 * - Else returns idle_task.
 */
static struct task_struct *
pick_task(struct rq *rq, const struct sched_class *class, struct task_struct *max, bool in_fi)
{
        struct task_struct *class_pick, *cookie_pick;
        unsigned long cookie = rq->core->core_cookie;

        class_pick = class->pick_task(rq);
        if (!class_pick)
                return NULL;

        if (!cookie) {
                /*
                 * If class_pick is tagged, return it only if it has
                 * higher priority than max.
                 */
                if (max && class_pick->core_cookie &&
                    prio_less(class_pick, max, in_fi))
                        return idle_sched_class.pick_task(rq);

                return class_pick;
        }

        /*
         * If class_pick is idle or matches cookie, return early.
         */
        if (cookie_equals(class_pick, cookie))
                return class_pick;

        cookie_pick = sched_core_find(rq, cookie);

        /*
         * If class > max && class > cookie, it is the highest priority task on
         * the core (so far) and it must be selected, otherwise we must go with
         * the cookie pick in order to satisfy the constraint.
         */
        if (prio_less(cookie_pick, class_pick, in_fi) &&
            (!max || prio_less(max, class_pick, in_fi)))
                return class_pick;

        return cookie_pick;
}

extern void task_vruntime_update(struct rq *rq, struct task_struct *p, bool in_fi);

static struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
        struct task_struct *next, *max = NULL;
        const struct sched_class *class;
        const struct cpumask *smt_mask;
        bool fi_before = false;
        int i, j, cpu, occ = 0;
        bool need_sync;

        if (!sched_core_enabled(rq))
                return __pick_next_task(rq, prev, rf);

        cpu = cpu_of(rq);

        /* Stopper task is switching into idle, no need core-wide selection. */
        if (cpu_is_offline(cpu)) {
                /*
                 * Reset core_pick so that we don't enter the fastpath when
                 * coming online. core_pick would already be migrated to
                 * another cpu during offline.
                 */
                rq->core_pick = NULL;
                return __pick_next_task(rq, prev, rf);
        }

        /*
         * If there were no {en,de}queues since we picked (IOW, the task
         * pointers are all still valid), and we haven't scheduled the last
         * pick yet, do so now.
         *
         * rq->core_pick can be NULL if no selection was made for a CPU because
         * it was either offline or went offline during a sibling's core-wide
         * selection. In this case, do a core-wide selection.
         */
        if (rq->core->core_pick_seq == rq->core->core_task_seq &&
            rq->core->core_pick_seq != rq->core_sched_seq &&
            rq->core_pick) {
                WRITE_ONCE(rq->core_sched_seq, rq->core->core_pick_seq);

                next = rq->core_pick;
                if (next != prev) {
                        put_prev_task(rq, prev);
                        set_next_task(rq, next);
                }

                rq->core_pick = NULL;
                return next;
        }

        put_prev_task_balance(rq, prev, rf);

        smt_mask = cpu_smt_mask(cpu);
        need_sync = !!rq->core->core_cookie;

        /* reset state */
        rq->core->core_cookie = 0UL;
        if (rq->core->core_forceidle) {
                need_sync = true;
                fi_before = true;
                rq->core->core_forceidle = false;
        }

        /*
         * core->core_task_seq, core->core_pick_seq, rq->core_sched_seq
         *
         * @task_seq guards the task state ({en,de}queues)
         * @pick_seq is the @task_seq we did a selection on
         * @sched_seq is the @pick_seq we scheduled
         *
         * However, preemptions can cause multiple picks on the same task set.
         * 'Fix' this by also increasing @task_seq for every pick.
         */
        rq->core->core_task_seq++;

        /*
         * Optimize for common case where this CPU has no cookies
         * and there are no cookied tasks running on siblings.
         */
        if (!need_sync) {
                for_each_class(class) {
                        next = class->pick_task(rq);
                        if (next)
                                break;
                }

                if (!next->core_cookie) {
                        rq->core_pick = NULL;
                        /*
                         * For robustness, update the min_vruntime_fi for
                         * unconstrained picks as well.
                         */
                        WARN_ON_ONCE(fi_before);
                        task_vruntime_update(rq, next, false);
                        goto done;
                }
        }

        for_each_cpu(i, smt_mask) {
                struct rq *rq_i = cpu_rq(i);

                rq_i->core_pick = NULL;

                if (i != cpu)
                        update_rq_clock(rq_i);
        }

        /*
         * Try and select tasks for each sibling in descending sched_class
         * order.
         */
        for_each_class(class) {
again:
                for_each_cpu_wrap(i, smt_mask, cpu) {
                        struct rq *rq_i = cpu_rq(i);
                        struct task_struct *p;

                        if (rq_i->core_pick)
                                continue;

                        /*
                         * If this sibling doesn't yet have a suitable task to
                         * run; ask for the most eligible task, given the
                         * highest priority task already selected for this
                         * core.
                         */
                        p = pick_task(rq_i, class, max, fi_before);
                        if (!p)
                                continue;

                        if (!is_task_rq_idle(p))
                                occ++;

                        rq_i->core_pick = p;
                        if (rq_i->idle == p && rq_i->nr_running) {
                                rq->core->core_forceidle = true;
                                if (!fi_before)
                                        rq->core->core_forceidle_seq++;
                        }

                        /*
                         * If this new candidate is of higher priority than the
                         * previous; and they're incompatible; we need to wipe
                         * the slate and start over. pick_task makes sure that
                         * p's priority is more than max if it doesn't match
                         * max's cookie.
                         *
                         * NOTE: this is a linear max-filter and is thus bounded
                         * in execution time.
                         */
                        if (!max || !cookie_match(max, p)) {
                                struct task_struct *old_max = max;

                                rq->core->core_cookie = p->core_cookie;
                                max = p;

                                if (old_max) {
                                        rq->core->core_forceidle = false;
                                        for_each_cpu(j, smt_mask) {
                                                if (j == i)
                                                        continue;

                                                cpu_rq(j)->core_pick = NULL;
                                        }
                                        occ = 1;
                                        goto again;
                                }
                        }
                }
        }

        rq->core->core_pick_seq = rq->core->core_task_seq;
        next = rq->core_pick;
        rq->core_sched_seq = rq->core->core_pick_seq;

        /* Something should have been selected for current CPU */
        WARN_ON_ONCE(!next);

        /*
         * Reschedule siblings
         *
         * NOTE: L1TF -- at this point we're no longer running the old task and
         * sending an IPI (below) ensures the sibling will no longer be running
         * their task. This ensures there is no inter-sibling overlap between
         * non-matching user state.
         */
        for_each_cpu(i, smt_mask) {
                struct rq *rq_i = cpu_rq(i);

                /*
                 * An online sibling might have gone offline before a task
                 * could be picked for it, or it might be offline but later
                 * happen to come online, but its too late and nothing was
                 * picked for it.  That's Ok - it will pick tasks for itself,
                 * so ignore it.
                 */
                if (!rq_i->core_pick)
                        continue;

                /*
                 * Update for new !FI->FI transitions, or if continuing to be in !FI:
                 * fi_before     fi      update?
                 *  0            0       1
                 *  0            1       1
                 *  1            0       1
                 *  1            1       0
                 */
                if (!(fi_before && rq->core->core_forceidle))
                        task_vruntime_update(rq_i, rq_i->core_pick, rq->core->core_forceidle);

                rq_i->core_pick->core_occupation = occ;

                if (i == cpu) {
                        rq_i->core_pick = NULL;
                        continue;
                }

                /* Did we break L1TF mitigation requirements? */
                WARN_ON_ONCE(!cookie_match(next, rq_i->core_pick));

                if (rq_i->curr == rq_i->core_pick) {
                        rq_i->core_pick = NULL;
                        continue;
                }

                resched_curr(rq_i);
        }

done:
        set_next_task(rq, next);
        return next;
}

static bool try_steal_cookie(int this, int that)
{
        struct rq *dst = cpu_rq(this), *src = cpu_rq(that);
        struct task_struct *p;
        unsigned long cookie;
        bool success = false;

        local_irq_disable();
        double_rq_lock(dst, src);

        cookie = dst->core->core_cookie;
        if (!cookie)
                goto unlock;

        if (dst->curr != dst->idle)
                goto unlock;

        p = sched_core_find(src, cookie);
        if (p == src->idle)
                goto unlock;

        do {
                if (p == src->core_pick || p == src->curr)
                        goto next;

                if (!is_cpu_allowed(p, this))
                        goto next;

                if (p->core_occupation > dst->idle->core_occupation)
                        goto next;

                deactivate_task(src, p, 0);
                set_task_cpu(p, this);
                activate_task(dst, p, 0);

                resched_curr(dst);

                success = true;
                break;

next:
                p = sched_core_next(p, cookie);
        } while (p);

unlock:
        double_rq_unlock(dst, src);
        local_irq_enable();

        return success;
}

static bool steal_cookie_task(int cpu, struct sched_domain *sd)
{
        int i;

        for_each_cpu_wrap(i, sched_domain_span(sd), cpu) {
                if (i == cpu)
                        continue;

                if (need_resched())
                        break;

                if (try_steal_cookie(cpu, i))
                        return true;
        }

        return false;
}

static void sched_core_balance(struct rq *rq)
{
        struct sched_domain *sd;
        int cpu = cpu_of(rq);

        preempt_disable();
        rcu_read_lock();
        raw_spin_rq_unlock_irq(rq);
        for_each_domain(cpu, sd) {
                if (need_resched())
                        break;

                if (steal_cookie_task(cpu, sd))
                        break;
        }
        raw_spin_rq_lock_irq(rq);
        rcu_read_unlock();
        preempt_enable();
}

static DEFINE_PER_CPU(struct callback_head, core_balance_head);

void queue_core_balance(struct rq *rq)
{
        if (!sched_core_enabled(rq))
                return;

        if (!rq->core->core_cookie)
                return;

        if (!rq->nr_running) /* not forced idle */
                return;

        queue_balance_callback(rq, &per_cpu(core_balance_head, rq->cpu), sched_core_balance);
}

static void sched_core_cpu_starting(unsigned int cpu)
{
        const struct cpumask *smt_mask = cpu_smt_mask(cpu);
        struct rq *rq = cpu_rq(cpu), *core_rq = NULL;
        unsigned long flags;
        int t;

        sched_core_lock(cpu, &flags);

        WARN_ON_ONCE(rq->core != rq);

        /* if we're the first, we'll be our own leader */
        if (cpumask_weight(smt_mask) == 1)
                goto unlock;

        /* find the leader */
        for_each_cpu(t, smt_mask) {
                if (t == cpu)
                        continue;
                rq = cpu_rq(t);
                if (rq->core == rq) {
                        core_rq = rq;
                        break;
                }
        }

        if (WARN_ON_ONCE(!core_rq)) /* whoopsie */
                goto unlock;

        /* install and validate core_rq */
        for_each_cpu(t, smt_mask) {
                rq = cpu_rq(t);

                if (t == cpu)
                        rq->core = core_rq;

                WARN_ON_ONCE(rq->core != core_rq);
        }

unlock:
        sched_core_unlock(cpu, &flags);
}

static void sched_core_cpu_deactivate(unsigned int cpu)
{
        const struct cpumask *smt_mask = cpu_smt_mask(cpu);
        struct rq *rq = cpu_rq(cpu), *core_rq = NULL;
        unsigned long flags;
        int t;

        sched_core_lock(cpu, &flags);

        /* if we're the last man standing, nothing to do */
        if (cpumask_weight(smt_mask) == 1) {
                WARN_ON_ONCE(rq->core != rq);
                goto unlock;
        }

        /* if we're not the leader, nothing to do */
        if (rq->core != rq)
                goto unlock;

        /* find a new leader */
        for_each_cpu(t, smt_mask) {
                if (t == cpu)
                        continue;
                core_rq = cpu_rq(t);
                break;
        }

        if (WARN_ON_ONCE(!core_rq)) /* impossible */
                goto unlock;

        /* copy the shared state to the new leader */
        core_rq->core_task_seq      = rq->core_task_seq;
        core_rq->core_pick_seq      = rq->core_pick_seq;
        core_rq->core_cookie        = rq->core_cookie;
        core_rq->core_forceidle     = rq->core_forceidle;
        core_rq->core_forceidle_seq = rq->core_forceidle_seq;

        /* install new leader */
        for_each_cpu(t, smt_mask) {
                rq = cpu_rq(t);
                rq->core = core_rq;
        }

unlock:
        sched_core_unlock(cpu, &flags);
}

static inline void sched_core_cpu_dying(unsigned int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (rq->core != rq)
                rq->core = rq;
}

#else /* !CONFIG_SCHED_CORE */

static inline void sched_core_cpu_starting(unsigned int cpu) {}
static inline void sched_core_cpu_deactivate(unsigned int cpu) {}
static inline void sched_core_cpu_dying(unsigned int cpu) {}

static struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
        return __pick_next_task(rq, prev, rf);
}

#endif /* CONFIG_SCHED_CORE */

/*
 * Constants for the sched_mode argument of __schedule().
 *
 * The mode argument allows RT enabled kernels to differentiate a
 * preemption from blocking on an 'sleeping' spin/rwlock. Note that
 * SM_MASK_PREEMPT for !RT has all bits set, which allows the compiler to
 * optimize the AND operation out and just check for zero.
 */
#define SM_NONE                 0x0
#define SM_PREEMPT              0x1
#define SM_RTLOCK_WAIT          0x2

#ifndef CONFIG_PREEMPT_RT
# define SM_MASK_PREEMPT        (~0U)
#else
# define SM_MASK_PREEMPT        SM_PREEMPT
#endif

/*
 * __schedule() is the main scheduler function.
 *
 * The main means of driving the scheduler and thus entering this function are:
 *
 *   1. Explicit blocking: mutex, semaphore, waitqueue, etc.
 *
 *   2. TIF_NEED_RESCHED flag is checked on interrupt and userspace return
 *      paths. For example, see arch/x86/entry_64.S.
 *
 *      To drive preemption between tasks, the scheduler sets the flag in timer
 *      interrupt handler scheduler_tick().
 *
 *   3. Wakeups don't really cause entry into schedule(). They add a
 *      task to the run-queue and that's it.
 *
 *      Now, if the new task added to the run-queue preempts the current
 *      task, then the wakeup sets TIF_NEED_RESCHED and schedule() gets
 *      called on the nearest possible occasion:
 *
 *       - If the kernel is preemptible (CONFIG_PREEMPTION=y):
 *
 *         - in syscall or exception context, at the next outmost
 *           preempt_enable(). (this might be as soon as the wake_up()'s
 *           spin_unlock()!)
 *
 *         - in IRQ context, return from interrupt-handler to
 *           preemptible context
 *
 *       - If the kernel is not preemptible (CONFIG_PREEMPTION is not set)
 *         then at the next:
 *
 *          - cond_resched() call
 *          - explicit schedule() call
 *          - return from syscall or exception to user-space
 *          - return from interrupt-handler to user-space
 *
 * WARNING: must be called with preemption disabled!
 */
static void __sched notrace __schedule(unsigned int sched_mode)
{
        struct task_struct *prev, *next;
        unsigned long *switch_count;
        unsigned long prev_state;
        struct rq_flags rf;
        struct rq *rq;
        int cpu;

        cpu = smp_processor_id();
        rq = cpu_rq(cpu);
        prev = rq->curr;

        schedule_debug(prev, !!sched_mode);

        if (sched_feat(HRTICK) || sched_feat(HRTICK_DL))
                hrtick_clear(rq);

        local_irq_disable();
        rcu_note_context_switch(!!sched_mode);

        /*
         * Make sure that signal_pending_state()->signal_pending() below
         * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
         * done by the caller to avoid the race with signal_wake_up():
         *
         * __set_current_state(@state)          signal_wake_up()
         * schedule()                             set_tsk_thread_flag(p, TIF_SIGPENDING)
         *                                        wake_up_state(p, state)
         *   LOCK rq->lock                          LOCK p->pi_state
         *   smp_mb__after_spinlock()               smp_mb__after_spinlock()
         *     if (signal_pending_state())          if (p->state & @state)
         *
         * Also, the membarrier system call requires a full memory barrier
         * after coming from user-space, before storing to rq->curr.
         */
        rq_lock(rq, &rf);
        smp_mb__after_spinlock();

        /* Promote REQ to ACT */
        rq->clock_update_flags <<= 1;
        update_rq_clock(rq);

        switch_count = &prev->nivcsw;

        /*
         * We must load prev->state once (task_struct::state is volatile), such
         * that:
         *
         *  - we form a control dependency vs deactivate_task() below.
         *  - ptrace_{,un}freeze_traced() can change ->state underneath us.
         */
        prev_state = READ_ONCE(prev->__state);
        if (!(sched_mode & SM_MASK_PREEMPT) && prev_state) {
                if (signal_pending_state(prev_state, prev)) {
                        WRITE_ONCE(prev->__state, TASK_RUNNING);
                } else {
                        prev->sched_contributes_to_load =
                                (prev_state & TASK_UNINTERRUPTIBLE) &&
                                !(prev_state & TASK_NOLOAD) &&
                                !(prev->flags & PF_FROZEN);

                        if (prev->sched_contributes_to_load)
                                rq->nr_uninterruptible++;

                        /*
                         * __schedule()                 ttwu()
                         *   prev_state = prev->state;    if (p->on_rq && ...)
                         *   if (prev_state)                goto out;
                         *     p->on_rq = 0;              smp_acquire__after_ctrl_dep();
                         *                                p->state = TASK_WAKING
                         *
                         * Where __schedule() and ttwu() have matching control dependencies.
                         *
                         * After this, schedule() must not care about p->state any more.
                         */
                        deactivate_task(rq, prev, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);

                        if (prev->in_iowait) {
                                atomic_inc(&rq->nr_iowait);
                                delayacct_blkio_start();
                        }
                }
                switch_count = &prev->nvcsw;
        }

        next = pick_next_task(rq, prev, &rf);
        clear_tsk_need_resched(prev);
        clear_tsk_need_resched_lazy(prev);
        clear_preempt_need_resched();
#ifdef CONFIG_SCHED_DEBUG
        rq->last_seen_need_resched_ns = 0;
#endif

        if (likely(prev != next)) {
                rq->nr_switches++;
                /*
                 * RCU users of rcu_dereference(rq->curr) may not see
                 * changes to task_struct made by pick_next_task().
                 */
                RCU_INIT_POINTER(rq->curr, next);
                /*
                 * The membarrier system call requires each architecture
                 * to have a full memory barrier after updating
                 * rq->curr, before returning to user-space.
                 *
                 * Here are the schemes providing that barrier on the
                 * various architectures:
                 * - mm ? switch_mm() : mmdrop() for x86, s390, sparc, PowerPC.
                 *   switch_mm() rely on membarrier_arch_switch_mm() on PowerPC.
                 * - finish_lock_switch() for weakly-ordered
                 *   architectures where spin_unlock is a full barrier,
                 * - switch_to() for arm64 (weakly-ordered, spin_unlock
                 *   is a RELEASE barrier),
                 */
                ++*switch_count;

                migrate_disable_switch(rq, prev);
                psi_sched_switch(prev, next, !task_on_rq_queued(prev));

                trace_sched_switch(sched_mode & SM_MASK_PREEMPT, prev, next);

                /* Also unlocks the rq: */
                rq = context_switch(rq, prev, next, &rf);
        } else {
                rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);

                rq_unpin_lock(rq, &rf);
                __balance_callbacks(rq);
                raw_spin_rq_unlock_irq(rq);
        }
}

void __noreturn do_task_dead(void)
{
        /* Causes final put_task_struct in finish_task_switch(): */
        set_special_state(TASK_DEAD);

        /* Tell freezer to ignore us: */
        current->flags |= PF_NOFREEZE;

        __schedule(SM_NONE);
        BUG();

        /* Avoid "noreturn function does return" - but don't continue if BUG() is a NOP: */
        for (;;)
                cpu_relax();
}

static inline void sched_submit_work(struct task_struct *tsk)
{
        unsigned int task_flags;

        if (task_is_running(tsk))
                return;

        task_flags = tsk->flags;
        /*
         * If a worker went to sleep, notify and ask workqueue whether
         * it wants to wake up a task to maintain concurrency.
         * As this function is called inside the schedule() context,
         * we disable preemption to avoid it calling schedule() again
         * in the possible wakeup of a kworker and because wq_worker_sleeping()
         * requires it.
         */
        if (task_flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
                preempt_disable();
                if (task_flags & PF_WQ_WORKER)
                        wq_worker_sleeping(tsk);
                else
                        io_wq_worker_sleeping(tsk);
                preempt_enable_no_resched();
        }

        /*
         * spinlock and rwlock must not flush block requests.  This will
         * deadlock if the callback attempts to acquire a lock which is
         * already acquired.
         */
        SCHED_WARN_ON(current->__state & TASK_RTLOCK_WAIT);

        /*
         * If we are going to sleep and we have plugged IO queued,
         * make sure to submit it to avoid deadlocks.
         */
        if (blk_needs_flush_plug(tsk))
                blk_schedule_flush_plug(tsk);
}

static void sched_update_worker(struct task_struct *tsk)
{
        if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
                if (tsk->flags & PF_WQ_WORKER)
                        wq_worker_running(tsk);
                else
                        io_wq_worker_running(tsk);
        }
}

asmlinkage __visible void __sched schedule(void)
{
        struct task_struct *tsk = current;

        sched_submit_work(tsk);
        do {
                preempt_disable();
                __schedule(SM_NONE);
                sched_preempt_enable_no_resched();
        } while (need_resched());
        sched_update_worker(tsk);
}
EXPORT_SYMBOL(schedule);

/*
 * synchronize_rcu_tasks() makes sure that no task is stuck in preempted
 * state (have scheduled out non-voluntarily) by making sure that all
 * tasks have either left the run queue or have gone into user space.
 * As idle tasks do not do either, they must not ever be preempted
 * (schedule out non-voluntarily).
 *
 * schedule_idle() is similar to schedule_preempt_disable() except that it
 * never enables preemption because it does not call sched_submit_work().
 */
void __sched schedule_idle(void)
{
        /*
         * As this skips calling sched_submit_work(), which the idle task does
         * regardless because that function is a nop when the task is in a
         * TASK_RUNNING state, make sure this isn't used someplace that the
         * current task can be in any other state. Note, idle is always in the
         * TASK_RUNNING state.
         */
        WARN_ON_ONCE(current->__state);
        do {
                __schedule(SM_NONE);
        } while (need_resched());
}

#if defined(CONFIG_CONTEXT_TRACKING) && !defined(CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK)
asmlinkage __visible void __sched schedule_user(void)
{
        /*
         * If we come here after a random call to set_need_resched(),
         * or we have been woken up remotely but the IPI has not yet arrived,
         * we haven't yet exited the RCU idle mode. Do it here manually until
         * we find a better solution.
         *
         * NB: There are buggy callers of this function.  Ideally we
         * should warn if prev_state != CONTEXT_USER, but that will trigger
         * too frequently to make sense yet.
         */
        enum ctx_state prev_state = exception_enter();
        schedule();
        exception_exit(prev_state);
}
#endif

/**
 * schedule_preempt_disabled - called with preemption disabled
 *
 * Returns with preemption disabled. Note: preempt_count must be 1
 */
void __sched schedule_preempt_disabled(void)
{
        sched_preempt_enable_no_resched();
        schedule();
        preempt_disable();
}

#ifdef CONFIG_PREEMPT_RT
void __sched notrace schedule_rtlock(void)
{
        do {
                preempt_disable();
                __schedule(SM_RTLOCK_WAIT);
                sched_preempt_enable_no_resched();
        } while (need_resched());
}
NOKPROBE_SYMBOL(schedule_rtlock);
#endif

static void __sched notrace preempt_schedule_common(void)
{
        do {
                /*
                 * Because the function tracer can trace preempt_count_sub()
                 * and it also uses preempt_enable/disable_notrace(), if
                 * NEED_RESCHED is set, the preempt_enable_notrace() called
                 * by the function tracer will call this function again and
                 * cause infinite recursion.
                 *
                 * Preemption must be disabled here before the function
                 * tracer can trace. Break up preempt_disable() into two
                 * calls. One to disable preemption without fear of being
                 * traced. The other to still record the preemption latency,
                 * which can also be traced by the function tracer.
                 */
                preempt_disable_notrace();
                preempt_latency_start(1);
                __schedule(SM_PREEMPT);
                preempt_latency_stop(1);
                preempt_enable_no_resched_notrace();

                /*
                 * Check again in case we missed a preemption opportunity
                 * between schedule and now.
                 */
        } while (need_resched());
}

#ifdef CONFIG_PREEMPT_LAZY
/*
 * If TIF_NEED_RESCHED is then we allow to be scheduled away since this is
 * set by a RT task. Oterwise we try to avoid beeing scheduled out as long as
 * preempt_lazy_count counter >0.
 */
static __always_inline int preemptible_lazy(void)
{
        if (test_thread_flag(TIF_NEED_RESCHED))
                return 1;
        if (current_thread_info()->preempt_lazy_count)
                return 0;
        return 1;
}

#else

static inline int preemptible_lazy(void)
{
        return 1;
}

#endif

#ifdef CONFIG_PREEMPTION
/*
 * This is the entry point to schedule() from in-kernel preemption
 * off of preempt_enable.
 */
asmlinkage __visible void __sched notrace preempt_schedule(void)
{
        /*
         * If there is a non-zero preempt_count or interrupts are disabled,
         * we do not want to preempt the current task. Just return..
         */
        if (likely(!preemptible()))
                return;
        if (!preemptible_lazy())
                return;
        preempt_schedule_common();
}
NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);

#ifdef CONFIG_PREEMPT_DYNAMIC
DEFINE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
#endif


/**
 * preempt_schedule_notrace - preempt_schedule called by tracing
 *
 * The tracing infrastructure uses preempt_enable_notrace to prevent
 * recursion and tracing preempt enabling caused by the tracing
 * infrastructure itself. But as tracing can happen in areas coming
 * from userspace or just about to enter userspace, a preempt enable
 * can occur before user_exit() is called. This will cause the scheduler
 * to be called when the system is still in usermode.
 *
 * To prevent this, the preempt_enable_notrace will use this function
 * instead of preempt_schedule() to exit user context if needed before
 * calling the scheduler.
 */
asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
{
        enum ctx_state prev_ctx;

        if (likely(!preemptible()))
                return;

        if (!preemptible_lazy())
                return;

        do {
                /*
                 * Because the function tracer can trace preempt_count_sub()
                 * and it also uses preempt_enable/disable_notrace(), if
                 * NEED_RESCHED is set, the preempt_enable_notrace() called
                 * by the function tracer will call this function again and
                 * cause infinite recursion.
                 *
                 * Preemption must be disabled here before the function
                 * tracer can trace. Break up preempt_disable() into two
                 * calls. One to disable preemption without fear of being
                 * traced. The other to still record the preemption latency,
                 * which can also be traced by the function tracer.
                 */
                preempt_disable_notrace();
                preempt_latency_start(1);
                /*
                 * Needs preempt disabled in case user_exit() is traced
                 * and the tracer calls preempt_enable_notrace() causing
                 * an infinite recursion.
                 */
                prev_ctx = exception_enter();
                __schedule(SM_PREEMPT);
                exception_exit(prev_ctx);

                preempt_latency_stop(1);
                preempt_enable_no_resched_notrace();
        } while (need_resched());
}
EXPORT_SYMBOL_GPL(preempt_schedule_notrace);

#ifdef CONFIG_PREEMPT_DYNAMIC
DEFINE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
#endif

#endif /* CONFIG_PREEMPTION */

#ifdef CONFIG_PREEMPT_DYNAMIC

#include <linux/entry-common.h>

/*
 * SC:cond_resched
 * SC:might_resched
 * SC:preempt_schedule
 * SC:preempt_schedule_notrace
 * SC:irqentry_exit_cond_resched
 *
 *
 * NONE:
 *   cond_resched               <- __cond_resched
 *   might_resched              <- RET0
 *   preempt_schedule           <- NOP
 *   preempt_schedule_notrace   <- NOP
 *   irqentry_exit_cond_resched <- NOP
 *
 * VOLUNTARY:
 *   cond_resched               <- __cond_resched
 *   might_resched              <- __cond_resched
 *   preempt_schedule           <- NOP
 *   preempt_schedule_notrace   <- NOP
 *   irqentry_exit_cond_resched <- NOP
 *
 * FULL:
 *   cond_resched               <- RET0
 *   might_resched              <- RET0
 *   preempt_schedule           <- preempt_schedule
 *   preempt_schedule_notrace   <- preempt_schedule_notrace
 *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
 */

enum {
        preempt_dynamic_none = 0,
        preempt_dynamic_voluntary,
        preempt_dynamic_full,
};

int preempt_dynamic_mode = preempt_dynamic_full;

int sched_dynamic_mode(const char *str)
{
        if (!strcmp(str, "none"))
                return preempt_dynamic_none;

        if (!strcmp(str, "voluntary"))
                return preempt_dynamic_voluntary;

        if (!strcmp(str, "full"))
                return preempt_dynamic_full;

        return -EINVAL;
}

void sched_dynamic_update(int mode)
{
        /*
         * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
         * the ZERO state, which is invalid.
         */
        static_call_update(cond_resched, __cond_resched);
        static_call_update(might_resched, __cond_resched);
        static_call_update(preempt_schedule, __preempt_schedule_func);
        static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
        static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);

        switch (mode) {
        case preempt_dynamic_none:
                static_call_update(cond_resched, __cond_resched);
                static_call_update(might_resched, (void *)&__static_call_return0);
                static_call_update(preempt_schedule, NULL);
                static_call_update(preempt_schedule_notrace, NULL);
                static_call_update(irqentry_exit_cond_resched, NULL);
                pr_info("Dynamic Preempt: none\n");
                break;

        case preempt_dynamic_voluntary:
                static_call_update(cond_resched, __cond_resched);
                static_call_update(might_resched, __cond_resched);
                static_call_update(preempt_schedule, NULL);
                static_call_update(preempt_schedule_notrace, NULL);
                static_call_update(irqentry_exit_cond_resched, NULL);
                pr_info("Dynamic Preempt: voluntary\n");
                break;

        case preempt_dynamic_full:
                static_call_update(cond_resched, (void *)&__static_call_return0);
                static_call_update(might_resched, (void *)&__static_call_return0);
                static_call_update(preempt_schedule, __preempt_schedule_func);
                static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
                static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
                pr_info("Dynamic Preempt: full\n");
                break;
        }

        preempt_dynamic_mode = mode;
}

static int __init setup_preempt_mode(char *str)
{
        int mode = sched_dynamic_mode(str);
        if (mode < 0) {
                pr_warn("Dynamic Preempt: unsupported mode: %s\n", str);
                return 0;
        }

        sched_dynamic_update(mode);
        return 1;
}
__setup("preempt=", setup_preempt_mode);

#endif /* CONFIG_PREEMPT_DYNAMIC */

/*
 * This is the entry point to schedule() from kernel preemption
 * off of irq context.
 * Note, that this is called and return with irqs disabled. This will
 * protect us against recursive calling from irq.
 */
asmlinkage __visible void __sched preempt_schedule_irq(void)
{
        enum ctx_state prev_state;

        /* Catch callers which need to be fixed */
        BUG_ON(preempt_count() || !irqs_disabled());

        prev_state = exception_enter();

        do {
                preempt_disable();
                local_irq_enable();
                __schedule(SM_PREEMPT);
                local_irq_disable();
                sched_preempt_enable_no_resched();
        } while (need_resched());

        exception_exit(prev_state);
}

int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags,
                          void *key)
{
        WARN_ON_ONCE(IS_ENABLED(CONFIG_SCHED_DEBUG) && wake_flags & ~WF_SYNC);
        return try_to_wake_up(curr->private, mode, wake_flags);
}
EXPORT_SYMBOL(default_wake_function);

static void __setscheduler_prio(struct task_struct *p, int prio)
{
        if (dl_prio(prio))
                p->sched_class = &dl_sched_class;
        else if (rt_prio(prio))
                p->sched_class = &rt_sched_class;
        else
                p->sched_class = &fair_sched_class;

        p->prio = prio;
}

#ifdef CONFIG_RT_MUTEXES

static inline int __rt_effective_prio(struct task_struct *pi_task, int prio)
{
        if (pi_task)
                prio = min(prio, pi_task->prio);

        return prio;
}

static inline int rt_effective_prio(struct task_struct *p, int prio)
{
        struct task_struct *pi_task = rt_mutex_get_top_task(p);

        return __rt_effective_prio(pi_task, prio);
}

/*
 * rt_mutex_setprio - set the current priority of a task
 * @p: task to boost
 * @pi_task: donor task
 *
 * This function changes the 'effective' priority of a task. It does
 * not touch ->normal_prio like __setscheduler().
 *
 * Used by the rt_mutex code to implement priority inheritance
 * logic. Call site only calls if the priority of the task changed.
 */
void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
{
        int prio, oldprio, queued, running, queue_flag =
                DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
        const struct sched_class *prev_class;
        struct rq_flags rf;
        struct rq *rq;

        /* XXX used to be waiter->prio, not waiter->task->prio */
        prio = __rt_effective_prio(pi_task, p->normal_prio);

        /*
         * If nothing changed; bail early.
         */
        if (p->pi_top_task == pi_task && prio == p->prio && !dl_prio(prio))
                return;

        rq = __task_rq_lock(p, &rf);
        update_rq_clock(rq);
        /*
         * Set under pi_lock && rq->lock, such that the value can be used under
         * either lock.
         *
         * Note that there is loads of tricky to make this pointer cache work
         * right. rt_mutex_slowunlock()+rt_mutex_postunlock() work together to
         * ensure a task is de-boosted (pi_task is set to NULL) before the
         * task is allowed to run again (and can exit). This ensures the pointer
         * points to a blocked task -- which guarantees the task is present.
         */
        p->pi_top_task = pi_task;

        /*
         * For FIFO/RR we only need to set prio, if that matches we're done.
         */
        if (prio == p->prio && !dl_prio(prio))
                goto out_unlock;

        /*
         * Idle task boosting is a nono in general. There is one
         * exception, when PREEMPT_RT and NOHZ is active:
         *
         * The idle task calls get_next_timer_interrupt() and holds
         * the timer wheel base->lock on the CPU and another CPU wants
         * to access the timer (probably to cancel it). We can safely
         * ignore the boosting request, as the idle CPU runs this code
         * with interrupts disabled and will complete the lock
         * protected section without being interrupted. So there is no
         * real need to boost.
         */
        if (unlikely(p == rq->idle)) {
                WARN_ON(p != rq->curr);
                WARN_ON(p->pi_blocked_on);
                goto out_unlock;
        }

        trace_sched_pi_setprio(p, pi_task);
        oldprio = p->prio;

        if (oldprio == prio)
                queue_flag &= ~DEQUEUE_MOVE;

        prev_class = p->sched_class;
        queued = task_on_rq_queued(p);
        running = task_current(rq, p);
        if (queued)
                dequeue_task(rq, p, queue_flag);
        if (running)
                put_prev_task(rq, p);

        /*
         * Boosting condition are:
         * 1. -rt task is running and holds mutex A
         *      --> -dl task blocks on mutex A
         *
         * 2. -dl task is running and holds mutex A
         *      --> -dl task blocks on mutex A and could preempt the
         *          running task
         */
        if (dl_prio(prio)) {
                if (!dl_prio(p->normal_prio) ||
                    (pi_task && dl_prio(pi_task->prio) &&
                     dl_entity_preempt(&pi_task->dl, &p->dl))) {
                        p->dl.pi_se = pi_task->dl.pi_se;
                        queue_flag |= ENQUEUE_REPLENISH;
                } else {
                        p->dl.pi_se = &p->dl;
                }
        } else if (rt_prio(prio)) {
                if (dl_prio(oldprio))
                        p->dl.pi_se = &p->dl;
                if (oldprio < prio)
                        queue_flag |= ENQUEUE_HEAD;
        } else {
                if (dl_prio(oldprio))
                        p->dl.pi_se = &p->dl;
                if (rt_prio(oldprio))
                        p->rt.timeout = 0;
        }

        __setscheduler_prio(p, prio);

        if (queued)
                enqueue_task(rq, p, queue_flag);
        if (running)
                set_next_task(rq, p);

        check_class_changed(rq, p, prev_class, oldprio);
out_unlock:
        /* Avoid rq from going away on us: */
        preempt_disable();

        rq_unpin_lock(rq, &rf);
        __balance_callbacks(rq);
        raw_spin_rq_unlock(rq);

        preempt_enable();
}
#else
static inline int rt_effective_prio(struct task_struct *p, int prio)
{
        return prio;
}
#endif

void set_user_nice(struct task_struct *p, long nice)
{
        bool queued, running;
        int old_prio;
        struct rq_flags rf;
        struct rq *rq;

        if (task_nice(p) == nice || nice < MIN_NICE || nice > MAX_NICE)
                return;
        /*
         * We have to be careful, if called from sys_setpriority(),
         * the task might be in the middle of scheduling on another CPU.
         */
        rq = task_rq_lock(p, &rf);
        update_rq_clock(rq);

        /*
         * The RT priorities are set via sched_setscheduler(), but we still
         * allow the 'normal' nice value to be set - but as expected
         * it won't have any effect on scheduling until the task is
         * SCHED_DEADLINE, SCHED_FIFO or SCHED_RR:
         */
        if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
                p->static_prio = NICE_TO_PRIO(nice);
                goto out_unlock;
        }
        queued = task_on_rq_queued(p);
        running = task_current(rq, p);
        if (queued)
                dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
        if (running)
                put_prev_task(rq, p);

        p->static_prio = NICE_TO_PRIO(nice);
        set_load_weight(p, true);
        old_prio = p->prio;
        p->prio = effective_prio(p);

        if (queued)
                enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
        if (running)
                set_next_task(rq, p);

        /*
         * If the task increased its priority or is running and
         * lowered its priority, then reschedule its CPU:
         */
        p->sched_class->prio_changed(rq, p, old_prio);

out_unlock:
        task_rq_unlock(rq, p, &rf);
}
EXPORT_SYMBOL(set_user_nice);

/*
 * can_nice - check if a task can reduce its nice value
 * @p: task
 * @nice: nice value
 */
int can_nice(const struct task_struct *p, const int nice)
{
        /* Convert nice value [19,-20] to rlimit style value [1,40]: */
        int nice_rlim = nice_to_rlimit(nice);

        return (nice_rlim <= task_rlimit(p, RLIMIT_NICE) ||
                capable(CAP_SYS_NICE));
}

#ifdef __ARCH_WANT_SYS_NICE

/*
 * sys_nice - change the priority of the current process.
 * @increment: priority increment
 *
 * sys_setpriority is a more generic, but much slower function that
 * does similar things.
 */
SYSCALL_DEFINE1(nice, int, increment)
{
        long nice, retval;

        /*
         * Setpriority might change our priority at the same moment.
         * We don't have to worry. Conceptually one call occurs first
         * and we have a single winner.
         */
        increment = clamp(increment, -NICE_WIDTH, NICE_WIDTH);
        nice = task_nice(current) + increment;

        nice = clamp_val(nice, MIN_NICE, MAX_NICE);
        if (increment < 0 && !can_nice(current, nice))
                return -EPERM;

        retval = security_task_setnice(current, nice);
        if (retval)
                return retval;

        set_user_nice(current, nice);
        return 0;
}

#endif

/**
 * task_prio - return the priority value of a given task.
 * @p: the task in question.
 *
 * Return: The priority value as seen by users in /proc.
 *
 * sched policy         return value   kernel prio    user prio/nice
 *
 * normal, batch, idle     [0 ... 39]  [100 ... 139]          0/[-20 ... 19]
 * fifo, rr             [-2 ... -100]     [98 ... 0]  [1 ... 99]
 * deadline                     -101             -1           0
 */
int task_prio(const struct task_struct *p)
{
        return p->prio - MAX_RT_PRIO;
}

/**
 * idle_cpu - is a given CPU idle currently?
 * @cpu: the processor in question.
 *
 * Return: 1 if the CPU is currently idle. 0 otherwise.
 */
int idle_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (rq->curr != rq->idle)
                return 0;

        if (rq->nr_running)
                return 0;

#ifdef CONFIG_SMP
        if (rq->ttwu_pending)
                return 0;
#endif

        return 1;
}

/**
 * available_idle_cpu - is a given CPU idle for enqueuing work.
 * @cpu: the CPU in question.
 *
 * Return: 1 if the CPU is currently idle. 0 otherwise.
 */
int available_idle_cpu(int cpu)
{
        if (!idle_cpu(cpu))
                return 0;

        if (vcpu_is_preempted(cpu))
                return 0;

        return 1;
}

/**
 * idle_task - return the idle task for a given CPU.
 * @cpu: the processor in question.
 *
 * Return: The idle task for the CPU @cpu.
 */
struct task_struct *idle_task(int cpu)
{
        return cpu_rq(cpu)->idle;
}

#ifdef CONFIG_SMP
/*
 * This function computes an effective utilization for the given CPU, to be
 * used for frequency selection given the linear relation: f = u * f_max.
 *
 * The scheduler tracks the following metrics:
 *
 *   cpu_util_{cfs,rt,dl,irq}()
 *   cpu_bw_dl()
 *
 * Where the cfs,rt and dl util numbers are tracked with the same metric and
 * synchronized windows and are thus directly comparable.
 *
 * The cfs,rt,dl utilization are the running times measured with rq->clock_task
 * which excludes things like IRQ and steal-time. These latter are then accrued
 * in the irq utilization.
 *
 * The DL bandwidth number otoh is not a measured metric but a value computed
 * based on the task model parameters and gives the minimal utilization
 * required to meet deadlines.
 */
unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
                                 unsigned long max, enum cpu_util_type type,
                                 struct task_struct *p)
{
        unsigned long dl_util, util, irq;
        struct rq *rq = cpu_rq(cpu);

        if (!uclamp_is_used() &&
            type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt)) {
                return max;
        }

        /*
         * Early check to see if IRQ/steal time saturates the CPU, can be
         * because of inaccuracies in how we track these -- see
         * update_irq_load_avg().
         */
        irq = cpu_util_irq(rq);
        if (unlikely(irq >= max))
                return max;

        /*
         * Because the time spend on RT/DL tasks is visible as 'lost' time to
         * CFS tasks and we use the same metric to track the effective
         * utilization (PELT windows are synchronized) we can directly add them
         * to obtain the CPU's actual utilization.
         *
         * CFS and RT utilization can be boosted or capped, depending on
         * utilization clamp constraints requested by currently RUNNABLE
         * tasks.
         * When there are no CFS RUNNABLE tasks, clamps are released and
         * frequency will be gracefully reduced with the utilization decay.
         */
        util = util_cfs + cpu_util_rt(rq);
        if (type == FREQUENCY_UTIL)
                util = uclamp_rq_util_with(rq, util, p);

        dl_util = cpu_util_dl(rq);

        /*
         * For frequency selection we do not make cpu_util_dl() a permanent part
         * of this sum because we want to use cpu_bw_dl() later on, but we need
         * to check if the CFS+RT+DL sum is saturated (ie. no idle time) such
         * that we select f_max when there is no idle time.
         *
         * NOTE: numerical errors or stop class might cause us to not quite hit
         * saturation when we should -- something for later.
         */
        if (util + dl_util >= max)
                return max;

        /*
         * OTOH, for energy computation we need the estimated running time, so
         * include util_dl and ignore dl_bw.
         */
        if (type == ENERGY_UTIL)
                util += dl_util;

        /*
         * There is still idle time; further improve the number by using the
         * irq metric. Because IRQ/steal time is hidden from the task clock we
         * need to scale the task numbers:
         *
         *              max - irq
         *   U' = irq + --------- * U
         *                 max
         */
        util = scale_irq_capacity(util, irq, max);
        util += irq;

        /*
         * Bandwidth required by DEADLINE must always be granted while, for
         * FAIR and RT, we use blocked utilization of IDLE CPUs as a mechanism
         * to gracefully reduce the frequency when no tasks show up for longer
         * periods of time.
         *
         * Ideally we would like to set bw_dl as min/guaranteed freq and util +
         * bw_dl as requested freq. However, cpufreq is not yet ready for such
         * an interface. So, we only do the latter for now.
         */
        if (type == FREQUENCY_UTIL)
                util += cpu_bw_dl(rq);

        return min(max, util);
}

unsigned long sched_cpu_util(int cpu, unsigned long max)
{
        return effective_cpu_util(cpu, cpu_util_cfs(cpu_rq(cpu)), max,
                                  ENERGY_UTIL, NULL);
}
#endif /* CONFIG_SMP */

/**
 * find_process_by_pid - find a process with a matching PID value.
 * @pid: the pid in question.
 *
 * The task of @pid, if found. %NULL otherwise.
 */
static struct task_struct *find_process_by_pid(pid_t pid)
{
        return pid ? find_task_by_vpid(pid) : current;
}

/*
 * sched_setparam() passes in -1 for its policy, to let the functions
 * it calls know not to change it.
 */
#define SETPARAM_POLICY -1

static void __setscheduler_params(struct task_struct *p,
                const struct sched_attr *attr)
{
        int policy = attr->sched_policy;

        if (policy == SETPARAM_POLICY)
                policy = p->policy;

        p->policy = policy;

        if (dl_policy(policy))
                __setparam_dl(p, attr);
        else if (fair_policy(policy))
                p->static_prio = NICE_TO_PRIO(attr->sched_nice);

        /*
         * __sched_setscheduler() ensures attr->sched_priority == 0 when
         * !rt_policy. Always setting this ensures that things like
         * getparam()/getattr() don't report silly values for !rt tasks.
         */
        p->rt_priority = attr->sched_priority;
        p->normal_prio = normal_prio(p);
        set_load_weight(p, true);
}

/*
 * Check the target process has a UID that matches the current process's:
 */
static bool check_same_owner(struct task_struct *p)
{
        const struct cred *cred = current_cred(), *pcred;
        bool match;

        rcu_read_lock();
        pcred = __task_cred(p);
        match = (uid_eq(cred->euid, pcred->euid) ||
                 uid_eq(cred->euid, pcred->uid));
        rcu_read_unlock();
        return match;
}

static int __sched_setscheduler(struct task_struct *p,
                                const struct sched_attr *attr,
                                bool user, bool pi)
{
        int oldpolicy = -1, policy = attr->sched_policy;
        int retval, oldprio, newprio, queued, running;
        const struct sched_class *prev_class;
        struct callback_head *head;
        struct rq_flags rf;
        int reset_on_fork;
        int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
        struct rq *rq;

        /* The pi code expects interrupts enabled */
        BUG_ON(pi && in_interrupt());
recheck:
        /* Double check policy once rq lock held: */
        if (policy < 0) {
                reset_on_fork = p->sched_reset_on_fork;
                policy = oldpolicy = p->policy;
        } else {
                reset_on_fork = !!(attr->sched_flags & SCHED_FLAG_RESET_ON_FORK);

                if (!valid_policy(policy))
                        return -EINVAL;
        }

        if (attr->sched_flags & ~(SCHED_FLAG_ALL | SCHED_FLAG_SUGOV))
                return -EINVAL;

        /*
         * Valid priorities for SCHED_FIFO and SCHED_RR are
         * 1..MAX_RT_PRIO-1, valid priority for SCHED_NORMAL,
         * SCHED_BATCH and SCHED_IDLE is 0.
         */
        if (attr->sched_priority > MAX_RT_PRIO-1)
                return -EINVAL;
        if ((dl_policy(policy) && !__checkparam_dl(attr)) ||
            (rt_policy(policy) != (attr->sched_priority != 0)))
                return -EINVAL;

        /*
         * Allow unprivileged RT tasks to decrease priority:
         */
        if (user && !capable(CAP_SYS_NICE)) {
                if (fair_policy(policy)) {
                        if (attr->sched_nice < task_nice(p) &&
                            !can_nice(p, attr->sched_nice))
                                return -EPERM;
                }

                if (rt_policy(policy)) {
                        unsigned long rlim_rtprio =
                                        task_rlimit(p, RLIMIT_RTPRIO);

                        /* Can't set/change the rt policy: */
                        if (policy != p->policy && !rlim_rtprio)
                                return -EPERM;

                        /* Can't increase priority: */
                        if (attr->sched_priority > p->rt_priority &&
                            attr->sched_priority > rlim_rtprio)
                                return -EPERM;
                }

                 /*
                  * Can't set/change SCHED_DEADLINE policy at all for now
                  * (safest behavior); in the future we would like to allow
                  * unprivileged DL tasks to increase their relative deadline
                  * or reduce their runtime (both ways reducing utilization)
                  */
                if (dl_policy(policy))
                        return -EPERM;

                /*
                 * Treat SCHED_IDLE as nice 20. Only allow a switch to
                 * SCHED_NORMAL if the RLIMIT_NICE would normally permit it.
                 */
                if (task_has_idle_policy(p) && !idle_policy(policy)) {
                        if (!can_nice(p, task_nice(p)))
                                return -EPERM;
                }

                /* Can't change other user's priorities: */
                if (!check_same_owner(p))
                        return -EPERM;

                /* Normal users shall not reset the sched_reset_on_fork flag: */
                if (p->sched_reset_on_fork && !reset_on_fork)
                        return -EPERM;
        }

        if (user) {
                if (attr->sched_flags & SCHED_FLAG_SUGOV)
                        return -EINVAL;

                retval = security_task_setscheduler(p);
                if (retval)
                        return retval;
        }

        /* Update task specific "requested" clamps */
        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) {
                retval = uclamp_validate(p, attr);
                if (retval)
                        return retval;
        }

        if (pi)
                cpuset_read_lock();

        /*
         * Make sure no PI-waiters arrive (or leave) while we are
         * changing the priority of the task:
         *
         * To be able to change p->policy safely, the appropriate
         * runqueue lock must be held.
         */
        rq = task_rq_lock(p, &rf);
        update_rq_clock(rq);

        /*
         * Changing the policy of the stop threads its a very bad idea:
         */
        if (p == rq->stop) {
                retval = -EINVAL;
                goto unlock;
        }

        /*
         * If not changing anything there's no need to proceed further,
         * but store a possible modification of reset_on_fork.
         */
        if (unlikely(policy == p->policy)) {
                if (fair_policy(policy) && attr->sched_nice != task_nice(p))
                        goto change;
                if (rt_policy(policy) && attr->sched_priority != p->rt_priority)
                        goto change;
                if (dl_policy(policy) && dl_param_changed(p, attr))
                        goto change;
                if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
                        goto change;

                p->sched_reset_on_fork = reset_on_fork;
                retval = 0;
                goto unlock;
        }
change:

        if (user) {
#ifdef CONFIG_RT_GROUP_SCHED
                /*
                 * Do not allow realtime tasks into groups that have no runtime
                 * assigned.
                 */
                if (rt_bandwidth_enabled() && rt_policy(policy) &&
                                task_group(p)->rt_bandwidth.rt_runtime == 0 &&
                                !task_group_is_autogroup(task_group(p))) {
                        retval = -EPERM;
                        goto unlock;
                }
#endif
#ifdef CONFIG_SMP
                if (dl_bandwidth_enabled() && dl_policy(policy) &&
                                !(attr->sched_flags & SCHED_FLAG_SUGOV)) {
                        cpumask_t *span = rq->rd->span;

                        /*
                         * Don't allow tasks with an affinity mask smaller than
                         * the entire root_domain to become SCHED_DEADLINE. We
                         * will also fail if there's no bandwidth available.
                         */
                        if (!cpumask_subset(span, p->cpus_ptr) ||
                            rq->rd->dl_bw.bw == 0) {
                                retval = -EPERM;
                                goto unlock;
                        }
                }
#endif
        }

        /* Re-check policy now with rq lock held: */
        if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
                policy = oldpolicy = -1;
                task_rq_unlock(rq, p, &rf);
                if (pi)
                        cpuset_read_unlock();
                goto recheck;
        }

        /*
         * If setscheduling to SCHED_DEADLINE (or changing the parameters
         * of a SCHED_DEADLINE task) we need to check if enough bandwidth
         * is available.
         */
        if ((dl_policy(policy) || dl_task(p)) && sched_dl_overflow(p, policy, attr)) {
                retval = -EBUSY;
                goto unlock;
        }

        p->sched_reset_on_fork = reset_on_fork;
        oldprio = p->prio;

        newprio = __normal_prio(policy, attr->sched_priority, attr->sched_nice);
        if (pi) {
                /*
                 * Take priority boosted tasks into account. If the new
                 * effective priority is unchanged, we just store the new
                 * normal parameters and do not touch the scheduler class and
                 * the runqueue. This will be done when the task deboost
                 * itself.
                 */
                newprio = rt_effective_prio(p, newprio);
                if (newprio == oldprio)
                        queue_flags &= ~DEQUEUE_MOVE;
        }

        queued = task_on_rq_queued(p);
        running = task_current(rq, p);
        if (queued)
                dequeue_task(rq, p, queue_flags);
        if (running)
                put_prev_task(rq, p);

        prev_class = p->sched_class;

        if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)) {
                __setscheduler_params(p, attr);
                __setscheduler_prio(p, newprio);
        }
        __setscheduler_uclamp(p, attr);

        if (queued) {
                /*
                 * We enqueue to tail when the priority of a task is
                 * increased (user space view).
                 */
                if (oldprio < p->prio)
                        queue_flags |= ENQUEUE_HEAD;

                enqueue_task(rq, p, queue_flags);
        }
        if (running)
                set_next_task(rq, p);

        check_class_changed(rq, p, prev_class, oldprio);

        /* Avoid rq from going away on us: */
        preempt_disable();
        head = splice_balance_callbacks(rq);
        task_rq_unlock(rq, p, &rf);

        if (pi) {
                cpuset_read_unlock();
                rt_mutex_adjust_pi(p);
        }

        /* Run balance callbacks after we've adjusted the PI chain: */
        balance_callbacks(rq, head);
        preempt_enable();

        return 0;

unlock:
        task_rq_unlock(rq, p, &rf);
        if (pi)
                cpuset_read_unlock();
        return retval;
}

static int _sched_setscheduler(struct task_struct *p, int policy,
                               const struct sched_param *param, bool check)
{
        struct sched_attr attr = {
                .sched_policy   = policy,
                .sched_priority = param->sched_priority,
                .sched_nice     = PRIO_TO_NICE(p->static_prio),
        };

        /* Fixup the legacy SCHED_RESET_ON_FORK hack. */
        if ((policy != SETPARAM_POLICY) && (policy & SCHED_RESET_ON_FORK)) {
                attr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
                policy &= ~SCHED_RESET_ON_FORK;
                attr.sched_policy = policy;
        }

        return __sched_setscheduler(p, &attr, check, true);
}
/**
 * sched_setscheduler - change the scheduling policy and/or RT priority of a thread.
 * @p: the task in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Use sched_set_fifo(), read its comment.
 *
 * Return: 0 on success. An error code otherwise.
 *
 * NOTE that the task may be already dead.
 */
int sched_setscheduler(struct task_struct *p, int policy,
                       const struct sched_param *param)
{
        return _sched_setscheduler(p, policy, param, true);
}
EXPORT_SYMBOL_GPL(sched_setscheduler);

int sched_setattr(struct task_struct *p, const struct sched_attr *attr)
{
        return __sched_setscheduler(p, attr, true, true);
}
EXPORT_SYMBOL_GPL(sched_setattr);

int sched_setattr_nocheck(struct task_struct *p, const struct sched_attr *attr)
{
        return __sched_setscheduler(p, attr, false, true);
}
EXPORT_SYMBOL_GPL(sched_setattr_nocheck);

/**
 * sched_setscheduler_nocheck - change the scheduling policy and/or RT priority of a thread from kernelspace.
 * @p: the task in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Just like sched_setscheduler, only don't bother checking if the
 * current context has permission.  For example, this is needed in
 * stop_machine(): we create temporary high priority worker threads,
 * but our caller might not have that capability.
 *
 * Return: 0 on success. An error code otherwise.
 */
int sched_setscheduler_nocheck(struct task_struct *p, int policy,
                               const struct sched_param *param)
{
        return _sched_setscheduler(p, policy, param, false);
}
EXPORT_SYMBOL_GPL(sched_setscheduler_nocheck);

/*
 * SCHED_FIFO is a broken scheduler model; that is, it is fundamentally
 * incapable of resource management, which is the one thing an OS really should
 * be doing.
 *
 * This is of course the reason it is limited to privileged users only.
 *
 * Worse still; it is fundamentally impossible to compose static priority
 * workloads. You cannot take two correctly working static prio workloads
 * and smash them together and still expect them to work.
 *
 * For this reason 'all' FIFO tasks the kernel creates are basically at:
 *
 *   MAX_RT_PRIO / 2
 *
 * The administrator _MUST_ configure the system, the kernel simply doesn't
 * know enough information to make a sensible choice.
 */
void sched_set_fifo(struct task_struct *p)
{
        struct sched_param sp = { .sched_priority = MAX_RT_PRIO / 2 };
        WARN_ON_ONCE(sched_setscheduler_nocheck(p, SCHED_FIFO, &sp) != 0);
}
EXPORT_SYMBOL_GPL(sched_set_fifo);

/*
 * For when you don't much care about FIFO, but want to be above SCHED_NORMAL.
 */
void sched_set_fifo_low(struct task_struct *p)
{
        struct sched_param sp = { .sched_priority = 1 };
        WARN_ON_ONCE(sched_setscheduler_nocheck(p, SCHED_FIFO, &sp) != 0);
}
EXPORT_SYMBOL_GPL(sched_set_fifo_low);

void sched_set_normal(struct task_struct *p, int nice)
{
        struct sched_attr attr = {
                .sched_policy = SCHED_NORMAL,
                .sched_nice = nice,
        };
        WARN_ON_ONCE(sched_setattr_nocheck(p, &attr) != 0);
}
EXPORT_SYMBOL_GPL(sched_set_normal);

static int
do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
{
        struct sched_param lparam;
        struct task_struct *p;
        int retval;

        if (!param || pid < 0)
                return -EINVAL;
        if (copy_from_user(&lparam, param, sizeof(struct sched_param)))
                return -EFAULT;

        rcu_read_lock();
        retval = -ESRCH;
        p = find_process_by_pid(pid);
        if (likely(p))
                get_task_struct(p);
        rcu_read_unlock();

        if (likely(p)) {
                retval = sched_setscheduler(p, policy, &lparam);
                put_task_struct(p);
        }

        return retval;
}

/*
 * Mimics kernel/events/core.c perf_copy_attr().
 */
static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *attr)
{
        u32 size;
        int ret;

        /* Zero the full structure, so that a short copy will be nice: */
        memset(attr, 0, sizeof(*attr));

        ret = get_user(size, &uattr->size);
        if (ret)
                return ret;

        /* ABI compatibility quirk: */
        if (!size)
                size = SCHED_ATTR_SIZE_VER0;
        if (size < SCHED_ATTR_SIZE_VER0 || size > PAGE_SIZE)
                goto err_size;

        ret = copy_struct_from_user(attr, sizeof(*attr), uattr, size);
        if (ret) {
                if (ret == -E2BIG)
                        goto err_size;
                return ret;
        }

        if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
            size < SCHED_ATTR_SIZE_VER1)
                return -EINVAL;

        /*
         * XXX: Do we want to be lenient like existing syscalls; or do we want
         * to be strict and return an error on out-of-bounds values?
         */
        attr->sched_nice = clamp(attr->sched_nice, MIN_NICE, MAX_NICE);

        return 0;

err_size:
        put_user(sizeof(*attr), &uattr->size);
        return -E2BIG;
}

static void get_params(struct task_struct *p, struct sched_attr *attr)
{
        if (task_has_dl_policy(p))
                __getparam_dl(p, attr);
        else if (task_has_rt_policy(p))
                attr->sched_priority = p->rt_priority;
        else
                attr->sched_nice = task_nice(p);
}

/**
 * sys_sched_setscheduler - set/change the scheduler policy and RT priority
 * @pid: the pid in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE3(sched_setscheduler, pid_t, pid, int, policy, struct sched_param __user *, param)
{
        if (policy < 0)
                return -EINVAL;

        return do_sched_setscheduler(pid, policy, param);
}

/**
 * sys_sched_setparam - set/change the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the new RT priority.
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE2(sched_setparam, pid_t, pid, struct sched_param __user *, param)
{
        return do_sched_setscheduler(pid, SETPARAM_POLICY, param);
}

/**
 * sys_sched_setattr - same as above, but with extended sched_attr
 * @pid: the pid in question.
 * @uattr: structure containing the extended parameters.
 * @flags: for future extension.
 */
SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
                               unsigned int, flags)
{
        struct sched_attr attr;
        struct task_struct *p;
        int retval;

        if (!uattr || pid < 0 || flags)
                return -EINVAL;

        retval = sched_copy_attr(uattr, &attr);
        if (retval)
                return retval;

        if ((int)attr.sched_policy < 0)
                return -EINVAL;
        if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY)
                attr.sched_policy = SETPARAM_POLICY;

        rcu_read_lock();
        retval = -ESRCH;
        p = find_process_by_pid(pid);
        if (likely(p))
                get_task_struct(p);
        rcu_read_unlock();

        if (likely(p)) {
                if (attr.sched_flags & SCHED_FLAG_KEEP_PARAMS)
                        get_params(p, &attr);
                retval = sched_setattr(p, &attr);
                put_task_struct(p);
        }

        return retval;
}

/**
 * sys_sched_getscheduler - get the policy (scheduling class) of a thread
 * @pid: the pid in question.
 *
 * Return: On success, the policy of the thread. Otherwise, a negative error
 * code.
 */
SYSCALL_DEFINE1(sched_getscheduler, pid_t, pid)
{
        struct task_struct *p;
        int retval;

        if (pid < 0)
                return -EINVAL;

        retval = -ESRCH;
        rcu_read_lock();
        p = find_process_by_pid(pid);
        if (p) {
                retval = security_task_getscheduler(p);
                if (!retval)
                        retval = p->policy
                                | (p->sched_reset_on_fork ? SCHED_RESET_ON_FORK : 0);
        }
        rcu_read_unlock();
        return retval;
}

/**
 * sys_sched_getparam - get the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the RT priority.
 *
 * Return: On success, 0 and the RT priority is in @param. Otherwise, an error
 * code.
 */
SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
{
        struct sched_param lp = { .sched_priority = 0 };
        struct task_struct *p;
        int retval;

        if (!param || pid < 0)
                return -EINVAL;

        rcu_read_lock();
        p = find_process_by_pid(pid);
        retval = -ESRCH;
        if (!p)
                goto out_unlock;

        retval = security_task_getscheduler(p);
        if (retval)
                goto out_unlock;

        if (task_has_rt_policy(p))
                lp.sched_priority = p->rt_priority;
        rcu_read_unlock();

        /*
         * This one might sleep, we cannot do it with a spinlock held ...
         */
        retval = copy_to_user(param, &lp, sizeof(*param)) ? -EFAULT : 0;

        return retval;

out_unlock:
        rcu_read_unlock();
        return retval;
}

/*
 * Copy the kernel size attribute structure (which might be larger
 * than what user-space knows about) to user-space.
 *
 * Note that all cases are valid: user-space buffer can be larger or
 * smaller than the kernel-space buffer. The usual case is that both
 * have the same size.
 */
static int
sched_attr_copy_to_user(struct sched_attr __user *uattr,
                        struct sched_attr *kattr,
                        unsigned int usize)
{
        unsigned int ksize = sizeof(*kattr);

        if (!access_ok(uattr, usize))
                return -EFAULT;

        /*
         * sched_getattr() ABI forwards and backwards compatibility:
         *
         * If usize == ksize then we just copy everything to user-space and all is good.
         *
         * If usize < ksize then we only copy as much as user-space has space for,
         * this keeps ABI compatibility as well. We skip the rest.
         *
         * If usize > ksize then user-space is using a newer version of the ABI,
         * which part the kernel doesn't know about. Just ignore it - tooling can
         * detect the kernel's knowledge of attributes from the attr->size value
         * which is set to ksize in this case.
         */
        kattr->size = min(usize, ksize);

        if (copy_to_user(uattr, kattr, kattr->size))
                return -EFAULT;

        return 0;
}

/**
 * sys_sched_getattr - similar to sched_getparam, but with sched_attr
 * @pid: the pid in question.
 * @uattr: structure containing the extended parameters.
 * @usize: sizeof(attr) for fwd/bwd comp.
 * @flags: for future extension.
 */
SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
                unsigned int, usize, unsigned int, flags)
{
        struct sched_attr kattr = { };
        struct task_struct *p;
        int retval;

        if (!uattr || pid < 0 || usize > PAGE_SIZE ||
            usize < SCHED_ATTR_SIZE_VER0 || flags)
                return -EINVAL;

        rcu_read_lock();
        p = find_process_by_pid(pid);
        retval = -ESRCH;
        if (!p)
                goto out_unlock;

        retval = security_task_getscheduler(p);
        if (retval)
                goto out_unlock;

        kattr.sched_policy = p->policy;
        if (p->sched_reset_on_fork)
                kattr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
        get_params(p, &kattr);
        kattr.sched_flags &= SCHED_FLAG_ALL;

#ifdef CONFIG_UCLAMP_TASK
        /*
         * This could race with another potential updater, but this is fine
         * because it'll correctly read the old or the new value. We don't need
         * to guarantee who wins the race as long as it doesn't return garbage.
         */
        kattr.sched_util_min = p->uclamp_req[UCLAMP_MIN].value;
        kattr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
#endif

        rcu_read_unlock();

        return sched_attr_copy_to_user(uattr, &kattr, usize);

out_unlock:
        rcu_read_unlock();
        return retval;
}

#ifdef CONFIG_SMP
int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
{
        int ret = 0;

        /*
         * If the task isn't a deadline task or admission control is
         * disabled then we don't care about affinity changes.
         */
        if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
                return 0;

        /*
         * Since bandwidth control happens on root_domain basis,
         * if admission test is enabled, we only admit -deadline
         * tasks allowed to run on all the CPUs in the task's
         * root_domain.
         */
        rcu_read_lock();
        if (!cpumask_subset(task_rq(p)->rd->span, mask))
                ret = -EBUSY;
        rcu_read_unlock();
        return ret;
}
#endif

static int
__sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
{
        int retval;
        cpumask_var_t cpus_allowed, new_mask;

        if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL))
                return -ENOMEM;

        if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
                retval = -ENOMEM;
                goto out_free_cpus_allowed;
        }

        cpuset_cpus_allowed(p, cpus_allowed);
        cpumask_and(new_mask, mask, cpus_allowed);

        retval = dl_task_check_affinity(p, new_mask);
        if (retval)
                goto out_free_new_mask;
again:
        retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | SCA_USER);
        if (retval)
                goto out_free_new_mask;

        cpuset_cpus_allowed(p, cpus_allowed);
        if (!cpumask_subset(new_mask, cpus_allowed)) {
                /*
                 * We must have raced with a concurrent cpuset update.
                 * Just reset the cpumask to the cpuset's cpus_allowed.
                 */
                cpumask_copy(new_mask, cpus_allowed);
                goto again;
        }

out_free_new_mask:
        free_cpumask_var(new_mask);
out_free_cpus_allowed:
        free_cpumask_var(cpus_allowed);
        return retval;
}

long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
{
        struct task_struct *p;
        int retval;

        rcu_read_lock();

        p = find_process_by_pid(pid);
        if (!p) {
                rcu_read_unlock();
                return -ESRCH;
        }

        /* Prevent p going away */
        get_task_struct(p);
        rcu_read_unlock();

        if (p->flags & PF_NO_SETAFFINITY) {
                retval = -EINVAL;
                goto out_put_task;
        }

        if (!check_same_owner(p)) {
                rcu_read_lock();
                if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
                        rcu_read_unlock();
                        retval = -EPERM;
                        goto out_put_task;
                }
                rcu_read_unlock();
        }

        retval = security_task_setscheduler(p);
        if (retval)
                goto out_put_task;

        retval = __sched_setaffinity(p, in_mask);
out_put_task:
        put_task_struct(p);
        return retval;
}

static int get_user_cpu_mask(unsigned long __user *user_mask_ptr, unsigned len,
                             struct cpumask *new_mask)
{
        if (len < cpumask_size())
                cpumask_clear(new_mask);
        else if (len > cpumask_size())
                len = cpumask_size();

        return copy_from_user(new_mask, user_mask_ptr, len) ? -EFAULT : 0;
}

/**
 * sys_sched_setaffinity - set the CPU affinity of a process
 * @pid: pid of the process
 * @len: length in bytes of the bitmask pointed to by user_mask_ptr
 * @user_mask_ptr: user-space pointer to the new CPU mask
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE3(sched_setaffinity, pid_t, pid, unsigned int, len,
                unsigned long __user *, user_mask_ptr)
{
        cpumask_var_t new_mask;
        int retval;

        if (!alloc_cpumask_var(&new_mask, GFP_KERNEL))
                return -ENOMEM;

        retval = get_user_cpu_mask(user_mask_ptr, len, new_mask);
        if (retval == 0)
                retval = sched_setaffinity(pid, new_mask);
        free_cpumask_var(new_mask);
        return retval;
}

long sched_getaffinity(pid_t pid, struct cpumask *mask)
{
        struct task_struct *p;
        unsigned long flags;
        int retval;

        rcu_read_lock();

        retval = -ESRCH;
        p = find_process_by_pid(pid);
        if (!p)
                goto out_unlock;

        retval = security_task_getscheduler(p);
        if (retval)
                goto out_unlock;

        raw_spin_lock_irqsave(&p->pi_lock, flags);
        cpumask_and(mask, &p->cpus_mask, cpu_active_mask);
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);

out_unlock:
        rcu_read_unlock();

        return retval;
}

/**
 * sys_sched_getaffinity - get the CPU affinity of a process
 * @pid: pid of the process
 * @len: length in bytes of the bitmask pointed to by user_mask_ptr
 * @user_mask_ptr: user-space pointer to hold the current CPU mask
 *
 * Return: size of CPU mask copied to user_mask_ptr on success. An
 * error code otherwise.
 */
SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len,
                unsigned long __user *, user_mask_ptr)
{
        int ret;
        cpumask_var_t mask;

        if ((len * BITS_PER_BYTE) < nr_cpu_ids)
                return -EINVAL;
        if (len & (sizeof(unsigned long)-1))
                return -EINVAL;

        if (!alloc_cpumask_var(&mask, GFP_KERNEL))
                return -ENOMEM;

        ret = sched_getaffinity(pid, mask);
        if (ret == 0) {
                unsigned int retlen = min(len, cpumask_size());

                if (copy_to_user(user_mask_ptr, mask, retlen))
                        ret = -EFAULT;
                else
                        ret = retlen;
        }
        free_cpumask_var(mask);

        return ret;
}

static void do_sched_yield(void)
{
        struct rq_flags rf;
        struct rq *rq;

        rq = this_rq_lock_irq(&rf);

        schedstat_inc(rq->yld_count);
        current->sched_class->yield_task(rq);

        preempt_disable();
        rq_unlock_irq(rq, &rf);
        sched_preempt_enable_no_resched();

        schedule();
}

/**
 * sys_sched_yield - yield the current processor to other threads.
 *
 * This function yields the current CPU to other tasks. If there are no
 * other threads running on this CPU then this function will return.
 *
 * Return: 0.
 */
SYSCALL_DEFINE0(sched_yield)
{
        do_sched_yield();
        return 0;
}

#if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
int __sched __cond_resched(void)
{
        if (should_resched(0)) {
                preempt_schedule_common();
                return 1;
        }
        /*
         * In preemptible kernels, ->rcu_read_lock_nesting tells the tick
         * whether the current CPU is in an RCU read-side critical section,
         * so the tick can report quiescent states even for CPUs looping
         * in kernel context.  In contrast, in non-preemptible kernels,
         * RCU readers leave no in-memory hints, which means that CPU-bound
         * processes executing in kernel context might never report an
         * RCU quiescent state.  Therefore, the following code causes
         * cond_resched() to report a quiescent state, but only when RCU
         * is in urgent need of one.
         */
#ifndef CONFIG_PREEMPT_RCU
        rcu_all_qs();
#endif
        return 0;
}
EXPORT_SYMBOL(__cond_resched);
#endif

#ifdef CONFIG_PREEMPT_DYNAMIC
DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(cond_resched);

DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(might_resched);
#endif

/*
 * __cond_resched_lock() - if a reschedule is pending, drop the given lock,
 * call schedule, and on return reacquire the lock.
 *
 * This works OK both with and without CONFIG_PREEMPTION. We do strange low-level
 * operations here to prevent schedule() from being called twice (once via
 * spin_unlock(), once by hand).
 */
int __cond_resched_lock(spinlock_t *lock)
{
        int resched = should_resched(PREEMPT_LOCK_OFFSET);
        int ret = 0;

        lockdep_assert_held(lock);

        if (spin_needbreak(lock) || resched) {
                spin_unlock(lock);
                if (!_cond_resched())
                        cpu_relax();
                ret = 1;
                spin_lock(lock);
        }
        return ret;
}
EXPORT_SYMBOL(__cond_resched_lock);

int __cond_resched_rwlock_read(rwlock_t *lock)
{
        int resched = should_resched(PREEMPT_LOCK_OFFSET);
        int ret = 0;

        lockdep_assert_held_read(lock);

        if (rwlock_needbreak(lock) || resched) {
                read_unlock(lock);
                if (!_cond_resched())
                        cpu_relax();
                ret = 1;
                read_lock(lock);
        }
        return ret;
}
EXPORT_SYMBOL(__cond_resched_rwlock_read);

int __cond_resched_rwlock_write(rwlock_t *lock)
{
        int resched = should_resched(PREEMPT_LOCK_OFFSET);
        int ret = 0;

        lockdep_assert_held_write(lock);

        if (rwlock_needbreak(lock) || resched) {
                write_unlock(lock);
                if (!_cond_resched())
                        cpu_relax();
                ret = 1;
                write_lock(lock);
        }
        return ret;
}
EXPORT_SYMBOL(__cond_resched_rwlock_write);

/**
 * yield - yield the current processor to other threads.
 *
 * Do not ever use this function, there's a 99% chance you're doing it wrong.
 *
 * The scheduler is at all times free to pick the calling task as the most
 * eligible task to run, if removing the yield() call from your code breaks
 * it, it's already broken.
 *
 * Typical broken usage is:
 *
 * while (!event)
 *      yield();
 *
 * where one assumes that yield() will let 'the other' process run that will
 * make event true. If the current task is a SCHED_FIFO task that will never
 * happen. Never use yield() as a progress guarantee!!
 *
 * If you want to use yield() to wait for something, use wait_event().
 * If you want to use yield() to be 'nice' for others, use cond_resched().
 * If you still want to use yield(), do not!
 */
void __sched yield(void)
{
        set_current_state(TASK_RUNNING);
        do_sched_yield();
}
EXPORT_SYMBOL(yield);

/**
 * yield_to - yield the current processor to another thread in
 * your thread group, or accelerate that thread toward the
 * processor it's on.
 * @p: target task
 * @preempt: whether task preemption is allowed or not
 *
 * It's the caller's job to ensure that the target task struct
 * can't go away on us before we can do any checks.
 *
 * Return:
 *      true (>0) if we indeed boosted the target task.
 *      false (0) if we failed to boost the target.
 *      -ESRCH if there's no task to yield to.
 */
int __sched yield_to(struct task_struct *p, bool preempt)
{
        struct task_struct *curr = current;
        struct rq *rq, *p_rq;
        unsigned long flags;
        int yielded = 0;

        local_irq_save(flags);
        rq = this_rq();

again:
        p_rq = task_rq(p);
        /*
         * If we're the only runnable task on the rq and target rq also
         * has only one task, there's absolutely no point in yielding.
         */
        if (rq->nr_running == 1 && p_rq->nr_running == 1) {
                yielded = -ESRCH;
                goto out_irq;
        }

        double_rq_lock(rq, p_rq);
        if (task_rq(p) != p_rq) {
                double_rq_unlock(rq, p_rq);
                goto again;
        }

        if (!curr->sched_class->yield_to_task)
                goto out_unlock;

        if (curr->sched_class != p->sched_class)
                goto out_unlock;

        if (task_running(p_rq, p) || !task_is_running(p))
                goto out_unlock;

        yielded = curr->sched_class->yield_to_task(rq, p);
        if (yielded) {
                schedstat_inc(rq->yld_count);
                /*
                 * Make p's CPU reschedule; pick_next_entity takes care of
                 * fairness.
                 */
                if (preempt && rq != p_rq)
                        resched_curr(p_rq);
        }

out_unlock:
        double_rq_unlock(rq, p_rq);
out_irq:
        local_irq_restore(flags);

        if (yielded > 0)
                schedule();

        return yielded;
}
EXPORT_SYMBOL_GPL(yield_to);

int io_schedule_prepare(void)
{
        int old_iowait = current->in_iowait;

        current->in_iowait = 1;
        blk_schedule_flush_plug(current);

        return old_iowait;
}

void io_schedule_finish(int token)
{
        current->in_iowait = token;
}

/*
 * This task is about to go to sleep on IO. Increment rq->nr_iowait so
 * that process accounting knows that this is a task in IO wait state.
 */
long __sched io_schedule_timeout(long timeout)
{
        int token;
        long ret;

        token = io_schedule_prepare();
        ret = schedule_timeout(timeout);
        io_schedule_finish(token);

        return ret;
}
EXPORT_SYMBOL(io_schedule_timeout);

void __sched io_schedule(void)
{
        int token;

        token = io_schedule_prepare();
        schedule();
        io_schedule_finish(token);
}
EXPORT_SYMBOL(io_schedule);

/**
 * sys_sched_get_priority_max - return maximum RT priority.
 * @policy: scheduling class.
 *
 * Return: On success, this syscall returns the maximum
 * rt_priority that can be used by a given scheduling class.
 * On failure, a negative error code is returned.
 */
SYSCALL_DEFINE1(sched_get_priority_max, int, policy)
{
        int ret = -EINVAL;

        switch (policy) {
        case SCHED_FIFO:
        case SCHED_RR:
                ret = MAX_RT_PRIO-1;
                break;
        case SCHED_DEADLINE:
        case SCHED_NORMAL:
        case SCHED_BATCH:
        case SCHED_IDLE:
                ret = 0;
                break;
        }
        return ret;
}

/**
 * sys_sched_get_priority_min - return minimum RT priority.
 * @policy: scheduling class.
 *
 * Return: On success, this syscall returns the minimum
 * rt_priority that can be used by a given scheduling class.
 * On failure, a negative error code is returned.
 */
SYSCALL_DEFINE1(sched_get_priority_min, int, policy)
{
        int ret = -EINVAL;

        switch (policy) {
        case SCHED_FIFO:
        case SCHED_RR:
                ret = 1;
                break;
        case SCHED_DEADLINE:
        case SCHED_NORMAL:
        case SCHED_BATCH:
        case SCHED_IDLE:
                ret = 0;
        }
        return ret;
}

static int sched_rr_get_interval(pid_t pid, struct timespec64 *t)
{
        struct task_struct *p;
        unsigned int time_slice;
        struct rq_flags rf;
        struct rq *rq;
        int retval;

        if (pid < 0)
                return -EINVAL;

        retval = -ESRCH;
        rcu_read_lock();
        p = find_process_by_pid(pid);
        if (!p)
                goto out_unlock;

        retval = security_task_getscheduler(p);
        if (retval)
                goto out_unlock;

        rq = task_rq_lock(p, &rf);
        time_slice = 0;
        if (p->sched_class->get_rr_interval)
                time_slice = p->sched_class->get_rr_interval(rq, p);
        task_rq_unlock(rq, p, &rf);

        rcu_read_unlock();
        jiffies_to_timespec64(time_slice, t);
        return 0;

out_unlock:
        rcu_read_unlock();
        return retval;
}

/**
 * sys_sched_rr_get_interval - return the default timeslice of a process.
 * @pid: pid of the process.
 * @interval: userspace pointer to the timeslice value.
 *
 * this syscall writes the default timeslice value of a given process
 * into the user-space timespec buffer. A value of '0' means infinity.
 *
 * Return: On success, 0 and the timeslice is in @interval. Otherwise,
 * an error code.
 */
SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
                struct __kernel_timespec __user *, interval)
{
        struct timespec64 t;
        int retval = sched_rr_get_interval(pid, &t);

        if (retval == 0)
                retval = put_timespec64(&t, interval);

        return retval;
}

#ifdef CONFIG_COMPAT_32BIT_TIME
SYSCALL_DEFINE2(sched_rr_get_interval_time32, pid_t, pid,
                struct old_timespec32 __user *, interval)
{
        struct timespec64 t;
        int retval = sched_rr_get_interval(pid, &t);

        if (retval == 0)
                retval = put_old_timespec32(&t, interval);
        return retval;
}
#endif

void sched_show_task(struct task_struct *p)
{
        unsigned long free = 0;
        int ppid;

        if (!try_get_task_stack(p))
                return;

        pr_info("task:%-15.15s state:%c", p->comm, task_state_to_char(p));

        if (task_is_running(p))
                pr_cont("  running task    ");
#ifdef CONFIG_DEBUG_STACK_USAGE
        free = stack_not_used(p);
#endif
        ppid = 0;
        rcu_read_lock();
        if (pid_alive(p))
                ppid = task_pid_nr(rcu_dereference(p->real_parent));
        rcu_read_unlock();
        pr_cont(" stack:%5lu pid:%5d ppid:%6d flags:0x%08lx\n",
                free, task_pid_nr(p), ppid,
                (unsigned long)task_thread_info(p)->flags);

        print_worker_info(KERN_INFO, p);
        print_stop_info(KERN_INFO, p);
        show_stack(p, NULL, KERN_INFO);
        put_task_stack(p);
}
EXPORT_SYMBOL_GPL(sched_show_task);

static inline bool
state_filter_match(unsigned long state_filter, struct task_struct *p)
{
        unsigned int state = READ_ONCE(p->__state);

        /* no filter, everything matches */
        if (!state_filter)
                return true;

        /* filter, but doesn't match */
        if (!(state & state_filter))
                return false;

        /*
         * When looking for TASK_UNINTERRUPTIBLE skip TASK_IDLE (allows
         * TASK_KILLABLE).
         */
        if (state_filter == TASK_UNINTERRUPTIBLE && state == TASK_IDLE)
                return false;

        return true;
}


void show_state_filter(unsigned int state_filter)
{
        struct task_struct *g, *p;

        rcu_read_lock();
        for_each_process_thread(g, p) {
                /*
                 * reset the NMI-timeout, listing all files on a slow
                 * console might take a lot of time:
                 * Also, reset softlockup watchdogs on all CPUs, because
                 * another CPU might be blocked waiting for us to process
                 * an IPI.
                 */
                touch_nmi_watchdog();
                touch_all_softlockup_watchdogs();
                if (state_filter_match(state_filter, p))
                        sched_show_task(p);
        }

#ifdef CONFIG_SCHED_DEBUG
        if (!state_filter)
                sysrq_sched_debug_show();
#endif
        rcu_read_unlock();
        /*
         * Only show locks if all tasks are dumped:
         */
        if (!state_filter)
                debug_show_all_locks();
}

/**
 * init_idle - set up an idle thread for a given CPU
 * @idle: task in question
 * @cpu: CPU the idle task belongs to
 *
 * NOTE: this function does not set the idle thread's NEED_RESCHED
 * flag, to make booting more robust.
 */
void __init init_idle(struct task_struct *idle, int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long flags;

        __sched_fork(0, idle);

        /*
         * The idle task doesn't need the kthread struct to function, but it
         * is dressed up as a per-CPU kthread and thus needs to play the part
         * if we want to avoid special-casing it in code that deals with per-CPU
         * kthreads.
         */
        set_kthread_struct(idle);

        raw_spin_lock_irqsave(&idle->pi_lock, flags);
        raw_spin_rq_lock(rq);

        idle->__state = TASK_RUNNING;
        idle->se.exec_start = sched_clock();
        /*
         * PF_KTHREAD should already be set at this point; regardless, make it
         * look like a proper per-CPU kthread.
         */
        idle->flags |= PF_IDLE | PF_KTHREAD | PF_NO_SETAFFINITY;
        kthread_set_per_cpu(idle, cpu);

#ifdef CONFIG_SMP
        /*
         * It's possible that init_idle() gets called multiple times on a task,
         * in that case do_set_cpus_allowed() will not do the right thing.
         *
         * And since this is boot we can forgo the serialization.
         */
        set_cpus_allowed_common(idle, cpumask_of(cpu), 0);
#endif
        /*
         * We're having a chicken and egg problem, even though we are
         * holding rq->lock, the CPU isn't yet set to this CPU so the
         * lockdep check in task_group() will fail.
         *
         * Similar case to sched_fork(). / Alternatively we could
         * use task_rq_lock() here and obtain the other rq->lock.
         *
         * Silence PROVE_RCU
         */
        rcu_read_lock();
        __set_task_cpu(idle, cpu);
        rcu_read_unlock();

        rq->idle = idle;
        rcu_assign_pointer(rq->curr, idle);
        idle->on_rq = TASK_ON_RQ_QUEUED;
#ifdef CONFIG_SMP
        idle->on_cpu = 1;
#endif
        raw_spin_rq_unlock(rq);
        raw_spin_unlock_irqrestore(&idle->pi_lock, flags);

        /* Set the preempt count _outside_ the spinlocks! */
        init_idle_preempt_count(idle, cpu);
#ifdef CONFIG_HAVE_PREEMPT_LAZY
        task_thread_info(idle)->preempt_lazy_count = 0;
#endif
        /*
         * The idle tasks have their own, simple scheduling class:
         */
        idle->sched_class = &idle_sched_class;
        ftrace_graph_init_idle_task(idle, cpu);
        vtime_init_idle(idle, cpu);
#ifdef CONFIG_SMP
        sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
#endif
}

#ifdef CONFIG_SMP

int cpuset_cpumask_can_shrink(const struct cpumask *cur,
                              const struct cpumask *trial)
{
        int ret = 1;

        if (!cpumask_weight(cur))
                return ret;

        ret = dl_cpuset_cpumask_can_shrink(cur, trial);

        return ret;
}

int task_can_attach(struct task_struct *p,
                    const struct cpumask *cs_effective_cpus)
{
        int ret = 0;

        /*
         * Kthreads which disallow setaffinity shouldn't be moved
         * to a new cpuset; we don't want to change their CPU
         * affinity and isolating such threads by their set of
         * allowed nodes is unnecessary.  Thus, cpusets are not
         * applicable for such threads.  This prevents checking for
         * success of set_cpus_allowed_ptr() on all attached tasks
         * before cpus_mask may be changed.
         */
        if (p->flags & PF_NO_SETAFFINITY) {
                ret = -EINVAL;
                goto out;
        }

        if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
                                              cs_effective_cpus)) {
                int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);

                if (unlikely(cpu >= nr_cpu_ids))
                        return -EINVAL;
                ret = dl_cpu_busy(cpu, p);
        }

out:
        return ret;
}

bool sched_smp_initialized __read_mostly;

#ifdef CONFIG_NUMA_BALANCING
/* Migrate current task p to target_cpu */
int migrate_task_to(struct task_struct *p, int target_cpu)
{
        struct migration_arg arg = { p, target_cpu };
        int curr_cpu = task_cpu(p);

        if (curr_cpu == target_cpu)
                return 0;

        if (!cpumask_test_cpu(target_cpu, p->cpus_ptr))
                return -EINVAL;

        /* TODO: This is not properly updating schedstats */

        trace_sched_move_numa(p, curr_cpu, target_cpu);
        return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
}

/*
 * Requeue a task on a given node and accurately track the number of NUMA
 * tasks on the runqueues
 */
void sched_setnuma(struct task_struct *p, int nid)
{
        bool queued, running;
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(p, &rf);
        queued = task_on_rq_queued(p);
        running = task_current(rq, p);

        if (queued)
                dequeue_task(rq, p, DEQUEUE_SAVE);
        if (running)
                put_prev_task(rq, p);

        p->numa_preferred_nid = nid;

        if (queued)
                enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
        if (running)
                set_next_task(rq, p);
        task_rq_unlock(rq, p, &rf);
}
#endif /* CONFIG_NUMA_BALANCING */

#ifdef CONFIG_HOTPLUG_CPU
/*
 * Ensure that the idle task is using init_mm right before its CPU goes
 * offline.
 */
void idle_task_exit(void)
{
        struct mm_struct *mm = current->active_mm;

        BUG_ON(cpu_online(smp_processor_id()));
        BUG_ON(current != this_rq()->idle);

        if (mm != &init_mm) {
                switch_mm(mm, &init_mm, current);
                finish_arch_post_lock_switch();
        }

        /* finish_cpu(), as ran on the BP, will clean up the active_mm state */
}

static int __balance_push_cpu_stop(void *arg)
{
        struct task_struct *p = arg;
        struct rq *rq = this_rq();
        struct rq_flags rf;
        int cpu;

        raw_spin_lock_irq(&p->pi_lock);
        rq_lock(rq, &rf);

        update_rq_clock(rq);

        if (task_rq(p) == rq && task_on_rq_queued(p)) {
                cpu = select_fallback_rq(rq->cpu, p);
                rq = __migrate_task(rq, &rf, p, cpu);
        }

        rq_unlock(rq, &rf);
        raw_spin_unlock_irq(&p->pi_lock);

        put_task_struct(p);

        return 0;
}

static DEFINE_PER_CPU(struct cpu_stop_work, push_work);

/*
 * Ensure we only run per-cpu kthreads once the CPU goes !active.
 *
 * This is enabled below SCHED_AP_ACTIVE; when !cpu_active(), but only
 * effective when the hotplug motion is down.
 */
static void balance_push(struct rq *rq)
{
        struct task_struct *push_task = rq->curr;

        lockdep_assert_rq_held(rq);

        /*
         * Ensure the thing is persistent until balance_push_set(.on = false);
         */
        rq->balance_callback = &balance_push_callback;

        /*
         * Only active while going offline and when invoked on the outgoing
         * CPU.
         */
        if (!cpu_dying(rq->cpu) || rq != this_rq())
                return;

        /*
         * Both the cpu-hotplug and stop task are in this case and are
         * required to complete the hotplug process.
         */
        if (kthread_is_per_cpu(push_task) ||
            is_migration_disabled(push_task)) {

                /*
                 * If this is the idle task on the outgoing CPU try to wake
                 * up the hotplug control thread which might wait for the
                 * last task to vanish. The rcuwait_active() check is
                 * accurate here because the waiter is pinned on this CPU
                 * and can't obviously be running in parallel.
                 *
                 * On RT kernels this also has to check whether there are
                 * pinned and scheduled out tasks on the runqueue. They
                 * need to leave the migrate disabled section first.
                 */
                if (!rq->nr_running && !rq_has_pinned_tasks(rq) &&
                    rcuwait_active(&rq->hotplug_wait)) {
                        raw_spin_rq_unlock(rq);
                        rcuwait_wake_up(&rq->hotplug_wait);
                        raw_spin_rq_lock(rq);
                }
                return;
        }

        get_task_struct(push_task);
        /*
         * Temporarily drop rq->lock such that we can wake-up the stop task.
         * Both preemption and IRQs are still disabled.
         */
        raw_spin_rq_unlock(rq);
        stop_one_cpu_nowait(rq->cpu, __balance_push_cpu_stop, push_task,
                            this_cpu_ptr(&push_work));
        /*
         * At this point need_resched() is true and we'll take the loop in
         * schedule(). The next pick is obviously going to be the stop task
         * which kthread_is_per_cpu() and will push this task away.
         */
        raw_spin_rq_lock(rq);
}

static void balance_push_set(int cpu, bool on)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        rq_lock_irqsave(rq, &rf);
        if (on) {
                WARN_ON_ONCE(rq->balance_callback);
                rq->balance_callback = &balance_push_callback;
        } else if (rq->balance_callback == &balance_push_callback) {
                rq->balance_callback = NULL;
        }
        rq_unlock_irqrestore(rq, &rf);
}

/*
 * Invoked from a CPUs hotplug control thread after the CPU has been marked
 * inactive. All tasks which are not per CPU kernel threads are either
 * pushed off this CPU now via balance_push() or placed on a different CPU
 * during wakeup. Wait until the CPU is quiescent.
 */
static void balance_hotplug_wait(void)
{
        struct rq *rq = this_rq();

        rcuwait_wait_event(&rq->hotplug_wait,
                           rq->nr_running == 1 && !rq_has_pinned_tasks(rq),
                           TASK_UNINTERRUPTIBLE);
}

#else

static inline void balance_push(struct rq *rq)
{
}

static inline void balance_push_set(int cpu, bool on)
{
}

static inline void balance_hotplug_wait(void)
{
}

#endif /* CONFIG_HOTPLUG_CPU */

void set_rq_online(struct rq *rq)
{
        if (!rq->online) {
                const struct sched_class *class;

                cpumask_set_cpu(rq->cpu, rq->rd->online);
                rq->online = 1;

                for_each_class(class) {
                        if (class->rq_online)
                                class->rq_online(rq);
                }
        }
}

void set_rq_offline(struct rq *rq)
{
        if (rq->online) {
                const struct sched_class *class;

                for_each_class(class) {
                        if (class->rq_offline)
                                class->rq_offline(rq);
                }

                cpumask_clear_cpu(rq->cpu, rq->rd->online);
                rq->online = 0;
        }
}

/*
 * used to mark begin/end of suspend/resume:
 */
static int num_cpus_frozen;

/*
 * Update cpusets according to cpu_active mask.  If cpusets are
 * disabled, cpuset_update_active_cpus() becomes a simple wrapper
 * around partition_sched_domains().
 *
 * If we come here as part of a suspend/resume, don't touch cpusets because we
 * want to restore it back to its original state upon resume anyway.
 */
static void cpuset_cpu_active(void)
{
        if (cpuhp_tasks_frozen) {
                /*
                 * num_cpus_frozen tracks how many CPUs are involved in suspend
                 * resume sequence. As long as this is not the last online
                 * operation in the resume sequence, just build a single sched
                 * domain, ignoring cpusets.
                 */
                partition_sched_domains(1, NULL, NULL);
                if (--num_cpus_frozen)
                        return;
                /*
                 * This is the last CPU online operation. So fall through and
                 * restore the original sched domains by considering the
                 * cpuset configurations.
                 */
                cpuset_force_rebuild();
        }
        cpuset_update_active_cpus();
}

static int cpuset_cpu_inactive(unsigned int cpu)
{
        if (!cpuhp_tasks_frozen) {
                int ret = dl_cpu_busy(cpu, NULL);

                if (ret)
                        return ret;
                cpuset_update_active_cpus();
        } else {
                num_cpus_frozen++;
                partition_sched_domains(1, NULL, NULL);
        }
        return 0;
}

int sched_cpu_activate(unsigned int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        /*
         * Clear the balance_push callback and prepare to schedule
         * regular tasks.
         */
        balance_push_set(cpu, false);

#ifdef CONFIG_SCHED_SMT
        /*
         * When going up, increment the number of cores with SMT present.
         */
        if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
                static_branch_inc_cpuslocked(&sched_smt_present);
#endif
        set_cpu_active(cpu, true);

        if (sched_smp_initialized) {
                sched_domains_numa_masks_set(cpu);
                cpuset_cpu_active();
        }

        /*
         * Put the rq online, if not already. This happens:
         *
         * 1) In the early boot process, because we build the real domains
         *    after all CPUs have been brought up.
         *
         * 2) At runtime, if cpuset_cpu_active() fails to rebuild the
         *    domains.
         */
        rq_lock_irqsave(rq, &rf);
        if (rq->rd) {
                BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
                set_rq_online(rq);
        }
        rq_unlock_irqrestore(rq, &rf);

        return 0;
}

int sched_cpu_deactivate(unsigned int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;
        int ret;

        /*
         * Remove CPU from nohz.idle_cpus_mask to prevent participating in
         * load balancing when not active
         */
        nohz_balance_exit_idle(rq);

        set_cpu_active(cpu, false);

        /*
         * From this point forward, this CPU will refuse to run any task that
         * is not: migrate_disable() or KTHREAD_IS_PER_CPU, and will actively
         * push those tasks away until this gets cleared, see
         * sched_cpu_dying().
         */
        balance_push_set(cpu, true);

        /*
         * We've cleared cpu_active_mask / set balance_push, wait for all
         * preempt-disabled and RCU users of this state to go away such that
         * all new such users will observe it.
         *
         * Specifically, we rely on ttwu to no longer target this CPU, see
         * ttwu_queue_cond() and is_cpu_allowed().
         *
         * Do sync before park smpboot threads to take care the rcu boost case.
         */
        synchronize_rcu();

        rq_lock_irqsave(rq, &rf);
        if (rq->rd) {
                update_rq_clock(rq);
                BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
                set_rq_offline(rq);
        }
        rq_unlock_irqrestore(rq, &rf);

#ifdef CONFIG_SCHED_SMT
        /*
         * When going down, decrement the number of cores with SMT present.
         */
        if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
                static_branch_dec_cpuslocked(&sched_smt_present);

        sched_core_cpu_deactivate(cpu);
#endif

        if (!sched_smp_initialized)
                return 0;

        ret = cpuset_cpu_inactive(cpu);
        if (ret) {
                balance_push_set(cpu, false);
                set_cpu_active(cpu, true);
                return ret;
        }
        sched_domains_numa_masks_clear(cpu);
        return 0;
}

static void sched_rq_cpu_starting(unsigned int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        rq->calc_load_update = calc_load_update;
        update_max_interval();
}

int sched_cpu_starting(unsigned int cpu)
{
        sched_core_cpu_starting(cpu);
        sched_rq_cpu_starting(cpu);
        sched_tick_start(cpu);
        return 0;
}

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Invoked immediately before the stopper thread is invoked to bring the
 * CPU down completely. At this point all per CPU kthreads except the
 * hotplug thread (current) and the stopper thread (inactive) have been
 * either parked or have been unbound from the outgoing CPU. Ensure that
 * any of those which might be on the way out are gone.
 *
 * If after this point a bound task is being woken on this CPU then the
 * responsible hotplug callback has failed to do it's job.
 * sched_cpu_dying() will catch it with the appropriate fireworks.
 */
int sched_cpu_wait_empty(unsigned int cpu)
{
        balance_hotplug_wait();
        return 0;
}

/*
 * Since this CPU is going 'away' for a while, fold any nr_active delta we
 * might have. Called from the CPU stopper task after ensuring that the
 * stopper is the last running task on the CPU, so nr_active count is
 * stable. We need to take the teardown thread which is calling this into
 * account, so we hand in adjust = 1 to the load calculation.
 *
 * Also see the comment "Global load-average calculations".
 */
static void calc_load_migrate(struct rq *rq)
{
        long delta = calc_load_fold_active(rq, 1);

        if (delta)
                atomic_long_add(delta, &calc_load_tasks);
}

static void dump_rq_tasks(struct rq *rq, const char *loglvl)
{
        struct task_struct *g, *p;
        int cpu = cpu_of(rq);

        lockdep_assert_rq_held(rq);

        printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running);
        for_each_process_thread(g, p) {
                if (task_cpu(p) != cpu)
                        continue;

                if (!task_on_rq_queued(p))
                        continue;

                printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm);
        }
}

int sched_cpu_dying(unsigned int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        /* Handle pending wakeups and then migrate everything off */
        sched_tick_stop(cpu);

        rq_lock_irqsave(rq, &rf);
        if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) {
                WARN(true, "Dying CPU not properly vacated!");
                dump_rq_tasks(rq, KERN_WARNING);
        }
        rq_unlock_irqrestore(rq, &rf);

        calc_load_migrate(rq);
        update_max_interval();
        hrtick_clear(rq);
        sched_core_cpu_dying(cpu);
        return 0;
}
#endif

void __init sched_init_smp(void)
{
        sched_init_numa();

        /*
         * There's no userspace yet to cause hotplug operations; hence all the
         * CPU masks are stable and all blatant races in the below code cannot
         * happen.
         */
        mutex_lock(&sched_domains_mutex);
        sched_init_domains(cpu_active_mask);
        mutex_unlock(&sched_domains_mutex);

        /* Move init over to a non-isolated CPU */
        if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0)
                BUG();
        current->flags &= ~PF_NO_SETAFFINITY;
        sched_init_granularity();

        init_sched_rt_class();
        init_sched_dl_class();

        sched_smp_initialized = true;
}

static int __init migration_init(void)
{
        sched_cpu_starting(smp_processor_id());
        return 0;
}
early_initcall(migration_init);

#else
void __init sched_init_smp(void)
{
        sched_init_granularity();
}
#endif /* CONFIG_SMP */

int in_sched_functions(unsigned long addr)
{
        return in_lock_functions(addr) ||
                (addr >= (unsigned long)__sched_text_start
                && addr < (unsigned long)__sched_text_end);
}

#ifdef CONFIG_CGROUP_SCHED
/*
 * Default task group.
 * Every task in system belongs to this group at bootup.
 */
struct task_group root_task_group;
LIST_HEAD(task_groups);

/* Cacheline aligned slab cache for task_group */
static struct kmem_cache *task_group_cache __read_mostly;
#endif

DECLARE_PER_CPU(cpumask_var_t, load_balance_mask);
DECLARE_PER_CPU(cpumask_var_t, select_idle_mask);

void __init sched_init(void)
{
        unsigned long ptr = 0;
        int i;

        /* Make sure the linker didn't screw up */
        BUG_ON(&idle_sched_class + 1 != &fair_sched_class ||
               &fair_sched_class + 1 != &rt_sched_class ||
               &rt_sched_class + 1   != &dl_sched_class);
#ifdef CONFIG_SMP
        BUG_ON(&dl_sched_class + 1 != &stop_sched_class);
#endif

        wait_bit_init();

#ifdef CONFIG_FAIR_GROUP_SCHED
        ptr += 2 * nr_cpu_ids * sizeof(void **);
#endif
#ifdef CONFIG_RT_GROUP_SCHED
        ptr += 2 * nr_cpu_ids * sizeof(void **);
#endif
        if (ptr) {
                ptr = (unsigned long)kzalloc(ptr, GFP_NOWAIT);

#ifdef CONFIG_FAIR_GROUP_SCHED
                root_task_group.se = (struct sched_entity **)ptr;
                ptr += nr_cpu_ids * sizeof(void **);

                root_task_group.cfs_rq = (struct cfs_rq **)ptr;
                ptr += nr_cpu_ids * sizeof(void **);

                root_task_group.shares = ROOT_TASK_GROUP_LOAD;
                init_cfs_bandwidth(&root_task_group.cfs_bandwidth);
#endif /* CONFIG_FAIR_GROUP_SCHED */
#ifdef CONFIG_RT_GROUP_SCHED
                root_task_group.rt_se = (struct sched_rt_entity **)ptr;
                ptr += nr_cpu_ids * sizeof(void **);

                root_task_group.rt_rq = (struct rt_rq **)ptr;
                ptr += nr_cpu_ids * sizeof(void **);

#endif /* CONFIG_RT_GROUP_SCHED */
        }
#ifdef CONFIG_CPUMASK_OFFSTACK
        for_each_possible_cpu(i) {
                per_cpu(load_balance_mask, i) = (cpumask_var_t)kzalloc_node(
                        cpumask_size(), GFP_KERNEL, cpu_to_node(i));
                per_cpu(select_idle_mask, i) = (cpumask_var_t)kzalloc_node(
                        cpumask_size(), GFP_KERNEL, cpu_to_node(i));
        }
#endif /* CONFIG_CPUMASK_OFFSTACK */

        init_rt_bandwidth(&def_rt_bandwidth, global_rt_period(), global_rt_runtime());
        init_dl_bandwidth(&def_dl_bandwidth, global_rt_period(), global_rt_runtime());

#ifdef CONFIG_SMP
        init_defrootdomain();
#endif

#ifdef CONFIG_RT_GROUP_SCHED
        init_rt_bandwidth(&root_task_group.rt_bandwidth,
                        global_rt_period(), global_rt_runtime());
#endif /* CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_CGROUP_SCHED
        task_group_cache = KMEM_CACHE(task_group, 0);

        list_add(&root_task_group.list, &task_groups);
        INIT_LIST_HEAD(&root_task_group.children);
        INIT_LIST_HEAD(&root_task_group.siblings);
        autogroup_init(&init_task);
#endif /* CONFIG_CGROUP_SCHED */

        for_each_possible_cpu(i) {
                struct rq *rq;

                rq = cpu_rq(i);
                raw_spin_lock_init(&rq->__lock);
                rq->nr_running = 0;
                rq->calc_load_active = 0;
                rq->calc_load_update = jiffies + LOAD_FREQ;
                init_cfs_rq(&rq->cfs);
                init_rt_rq(&rq->rt);
                init_dl_rq(&rq->dl);
#ifdef CONFIG_FAIR_GROUP_SCHED
                INIT_LIST_HEAD(&rq->leaf_cfs_rq_list);
                rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
                /*
                 * How much CPU bandwidth does root_task_group get?
                 *
                 * In case of task-groups formed thr' the cgroup filesystem, it
                 * gets 100% of the CPU resources in the system. This overall
                 * system CPU resource is divided among the tasks of
                 * root_task_group and its child task-groups in a fair manner,
                 * based on each entity's (task or task-group's) weight
                 * (se->load.weight).
                 *
                 * In other words, if root_task_group has 10 tasks of weight
                 * 1024) and two child groups A0 and A1 (of weight 1024 each),
                 * then A0's share of the CPU resource is:
                 *
                 *      A0's bandwidth = 1024 / (10*1024 + 1024 + 1024) = 8.33%
                 *
                 * We achieve this by letting root_task_group's tasks sit
                 * directly in rq->cfs (i.e root_task_group->se[] = NULL).
                 */
                init_tg_cfs_entry(&root_task_group, &rq->cfs, NULL, i, NULL);
#endif /* CONFIG_FAIR_GROUP_SCHED */

                rq->rt.rt_runtime = def_rt_bandwidth.rt_runtime;
#ifdef CONFIG_RT_GROUP_SCHED
                init_tg_rt_entry(&root_task_group, &rq->rt, NULL, i, NULL);
#endif
#ifdef CONFIG_SMP
                rq->sd = NULL;
                rq->rd = NULL;
                rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE;
                rq->balance_callback = &balance_push_callback;
                rq->active_balance = 0;
                rq->next_balance = jiffies;
                rq->push_cpu = 0;
                rq->cpu = i;
                rq->online = 0;
                rq->idle_stamp = 0;
                rq->avg_idle = 2*sysctl_sched_migration_cost;
                rq->wake_stamp = jiffies;
                rq->wake_avg_idle = rq->avg_idle;
                rq->max_idle_balance_cost = sysctl_sched_migration_cost;

                INIT_LIST_HEAD(&rq->cfs_tasks);

                rq_attach_root(rq, &def_root_domain);
#ifdef CONFIG_NO_HZ_COMMON
                rq->last_blocked_load_update_tick = jiffies;
                atomic_set(&rq->nohz_flags, 0);

                INIT_CSD(&rq->nohz_csd, nohz_csd_func, rq);
#endif
#ifdef CONFIG_HOTPLUG_CPU
                rcuwait_init(&rq->hotplug_wait);
#endif
#endif /* CONFIG_SMP */
                hrtick_rq_init(rq);
                atomic_set(&rq->nr_iowait, 0);

#ifdef CONFIG_SCHED_CORE
                rq->core = rq;
                rq->core_pick = NULL;
                rq->core_enabled = 0;
                rq->core_tree = RB_ROOT;
                rq->core_forceidle = false;

                rq->core_cookie = 0UL;
#endif
        }

        set_load_weight(&init_task, false);

        /*
         * The boot idle thread does lazy MMU switching as well:
         */
        mmgrab(&init_mm);
        enter_lazy_tlb(&init_mm, current);

        /*
         * Make us the idle thread. Technically, schedule() should not be
         * called from this thread, however somewhere below it might be,
         * but because we are the idle thread, we just pick up running again
         * when this runqueue becomes "idle".
         */
        init_idle(current, smp_processor_id());

        calc_load_update = jiffies + LOAD_FREQ;

#ifdef CONFIG_SMP
        idle_thread_set_boot_cpu();
        balance_push_set(smp_processor_id(), false);
#endif
        init_sched_fair_class();

        psi_init();

        init_uclamp();

        scheduler_running = 1;
}

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP

void __might_sleep(const char *file, int line)
{
        unsigned int state = get_current_state();
        /*
         * Blocking primitives will set (and therefore destroy) current->state,
         * since we will exit with TASK_RUNNING make sure we enter with it,
         * otherwise we will destroy state.
         */
        WARN_ONCE(state != TASK_RUNNING && current->task_state_change,
                        "do not call blocking ops when !TASK_RUNNING; "
                        "state=%x set at [<%p>] %pS\n", state,
                        (void *)current->task_state_change,
                        (void *)current->task_state_change);

        __might_resched(file, line, 0);
}
EXPORT_SYMBOL(__might_sleep);

static void print_preempt_disable_ip(int preempt_offset, unsigned long ip)
{
        if (!IS_ENABLED(CONFIG_DEBUG_PREEMPT))
                return;

        if (preempt_count() == preempt_offset)
                return;

        pr_err("Preemption disabled at:");
        print_ip_sym(KERN_ERR, ip);
}

static inline bool resched_offsets_ok(unsigned int offsets)
{
        unsigned int nested = preempt_count();

        nested += rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT;

        return nested == offsets;
}

void __might_resched(const char *file, int line, unsigned int offsets)
{
        /* Ratelimiting timestamp: */
        static unsigned long prev_jiffy;

        unsigned long preempt_disable_ip;

        /* WARN_ON_ONCE() by default, no rate limit required: */
        rcu_sleep_check();

        if ((resched_offsets_ok(offsets) && !irqs_disabled() &&
             !is_idle_task(current) && !current->non_block_count) ||
            system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING ||
            oops_in_progress)
                return;

        if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
                return;
        prev_jiffy = jiffies;

        /* Save this before calling printk(), since that will clobber it: */
        preempt_disable_ip = get_preempt_disable_ip(current);

        pr_err("BUG: sleeping function called from invalid context at %s:%d\n",
               file, line);
        pr_err("in_atomic(): %d, irqs_disabled(): %d, non_block: %d, pid: %d, name: %s\n",
               in_atomic(), irqs_disabled(), current->non_block_count,
               current->pid, current->comm);
        pr_err("preempt_count: %x, expected: %x\n", preempt_count(),
               offsets & MIGHT_RESCHED_PREEMPT_MASK);

        if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
                pr_err("RCU nest depth: %d, expected: %u\n",
                       rcu_preempt_depth(), offsets >> MIGHT_RESCHED_RCU_SHIFT);
        }

        if (task_stack_end_corrupted(current))
                pr_emerg("Thread overran stack, or stack corrupted\n");

        debug_show_held_locks(current);
        if (irqs_disabled())
                print_irqtrace_events(current);

        print_preempt_disable_ip(offsets & MIGHT_RESCHED_PREEMPT_MASK,
                                 preempt_disable_ip);

        dump_stack();
        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
EXPORT_SYMBOL(__might_resched);

void __cant_sleep(const char *file, int line, int preempt_offset)
{
        static unsigned long prev_jiffy;

        if (irqs_disabled())
                return;

        if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
                return;

        if (preempt_count() > preempt_offset)
                return;

        if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
                return;
        prev_jiffy = jiffies;

        printk(KERN_ERR "BUG: assuming atomic context at %s:%d\n", file, line);
        printk(KERN_ERR "in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n",
                        in_atomic(), irqs_disabled(),
                        current->pid, current->comm);

        debug_show_held_locks(current);
        dump_stack();
        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
EXPORT_SYMBOL_GPL(__cant_sleep);

#ifdef CONFIG_SMP
void __cant_migrate(const char *file, int line)
{
        static unsigned long prev_jiffy;

        if (irqs_disabled())
                return;

        if (is_migration_disabled(current))
                return;

        if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
                return;

        if (preempt_count() > 0)
                return;

        if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
                return;
        prev_jiffy = jiffies;

        pr_err("BUG: assuming non migratable context at %s:%d\n", file, line);
        pr_err("in_atomic(): %d, irqs_disabled(): %d, migration_disabled() %u pid: %d, name: %s\n",
               in_atomic(), irqs_disabled(), is_migration_disabled(current),
               current->pid, current->comm);

        debug_show_held_locks(current);
        dump_stack();
        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
EXPORT_SYMBOL_GPL(__cant_migrate);
#endif
#endif

#ifdef CONFIG_MAGIC_SYSRQ
void normalize_rt_tasks(void)
{
        struct task_struct *g, *p;
        struct sched_attr attr = {
                .sched_policy = SCHED_NORMAL,
        };

        read_lock(&tasklist_lock);
        for_each_process_thread(g, p) {
                /*
                 * Only normalize user tasks:
                 */
                if (p->flags & PF_KTHREAD)
                        continue;

                p->se.exec_start = 0;
                schedstat_set(p->se.statistics.wait_start,  0);
                schedstat_set(p->se.statistics.sleep_start, 0);
                schedstat_set(p->se.statistics.block_start, 0);

                if (!dl_task(p) && !rt_task(p)) {
                        /*
                         * Renice negative nice level userspace
                         * tasks back to 0:
                         */
                        if (task_nice(p) < 0)
                                set_user_nice(p, 0);
                        continue;
                }

                __sched_setscheduler(p, &attr, false, false);
        }
        read_unlock(&tasklist_lock);
}

#endif /* CONFIG_MAGIC_SYSRQ */

#if defined(CONFIG_IA64) || defined(CONFIG_KGDB_KDB)
/*
 * These functions are only useful for the IA64 MCA handling, or kdb.
 *
 * They can only be called when the whole system has been
 * stopped - every CPU needs to be quiescent, and no scheduling
 * activity can take place. Using them for anything else would
 * be a serious bug, and as a result, they aren't even visible
 * under any other configuration.
 */

/**
 * curr_task - return the current task for a given CPU.
 * @cpu: the processor in question.
 *
 * ONLY VALID WHEN THE WHOLE SYSTEM IS STOPPED!
 *
 * Return: The current task for @cpu.
 */
struct task_struct *curr_task(int cpu)
{
        return cpu_curr(cpu);
}

#endif /* defined(CONFIG_IA64) || defined(CONFIG_KGDB_KDB) */

#ifdef CONFIG_IA64
/**
 * ia64_set_curr_task - set the current task for a given CPU.
 * @cpu: the processor in question.
 * @p: the task pointer to set.
 *
 * Description: This function must only be used when non-maskable interrupts
 * are serviced on a separate stack. It allows the architecture to switch the
 * notion of the current task on a CPU in a non-blocking manner. This function
 * must be called with all CPU's synchronized, and interrupts disabled, the
 * and caller must save the original value of the current task (see
 * curr_task() above) and restore that value before reenabling interrupts and
 * re-starting the system.
 *
 * ONLY VALID WHEN THE WHOLE SYSTEM IS STOPPED!
 */
void ia64_set_curr_task(int cpu, struct task_struct *p)
{
        cpu_curr(cpu) = p;
}

#endif

#ifdef CONFIG_CGROUP_SCHED
/* task_group_lock serializes the addition/removal of task groups */
static DEFINE_SPINLOCK(task_group_lock);

static inline void alloc_uclamp_sched_group(struct task_group *tg,
                                            struct task_group *parent)
{
#ifdef CONFIG_UCLAMP_TASK_GROUP
        enum uclamp_id clamp_id;

        for_each_clamp_id(clamp_id) {
                uclamp_se_set(&tg->uclamp_req[clamp_id],
                              uclamp_none(clamp_id), false);
                tg->uclamp[clamp_id] = parent->uclamp[clamp_id];
        }
#endif
}

static void sched_free_group(struct task_group *tg)
{
        free_fair_sched_group(tg);
        free_rt_sched_group(tg);
        autogroup_free(tg);
        kmem_cache_free(task_group_cache, tg);
}

static void sched_free_group_rcu(struct rcu_head *rcu)
{
        sched_free_group(container_of(rcu, struct task_group, rcu));
}

static void sched_unregister_group(struct task_group *tg)
{
        unregister_fair_sched_group(tg);
        unregister_rt_sched_group(tg);
        /*
         * We have to wait for yet another RCU grace period to expire, as
         * print_cfs_stats() might run concurrently.
         */
        call_rcu(&tg->rcu, sched_free_group_rcu);
}

/* allocate runqueue etc for a new task group */
struct task_group *sched_create_group(struct task_group *parent)
{
        struct task_group *tg;

        tg = kmem_cache_alloc(task_group_cache, GFP_KERNEL | __GFP_ZERO);
        if (!tg)
                return ERR_PTR(-ENOMEM);

        if (!alloc_fair_sched_group(tg, parent))
                goto err;

        if (!alloc_rt_sched_group(tg, parent))
                goto err;

        alloc_uclamp_sched_group(tg, parent);

        return tg;

err:
        sched_free_group(tg);
        return ERR_PTR(-ENOMEM);
}

void sched_online_group(struct task_group *tg, struct task_group *parent)
{
        unsigned long flags;

        spin_lock_irqsave(&task_group_lock, flags);
        list_add_rcu(&tg->list, &task_groups);

        /* Root should already exist: */
        WARN_ON(!parent);

        tg->parent = parent;
        INIT_LIST_HEAD(&tg->children);
        list_add_rcu(&tg->siblings, &parent->children);
        spin_unlock_irqrestore(&task_group_lock, flags);

        online_fair_sched_group(tg);
}

/* rcu callback to free various structures associated with a task group */
static void sched_unregister_group_rcu(struct rcu_head *rhp)
{
        /* Now it should be safe to free those cfs_rqs: */
        sched_unregister_group(container_of(rhp, struct task_group, rcu));
}

void sched_destroy_group(struct task_group *tg)
{
        /* Wait for possible concurrent references to cfs_rqs complete: */
        call_rcu(&tg->rcu, sched_unregister_group_rcu);
}

void sched_release_group(struct task_group *tg)
{
        unsigned long flags;

        /*
         * Unlink first, to avoid walk_tg_tree_from() from finding us (via
         * sched_cfs_period_timer()).
         *
         * For this to be effective, we have to wait for all pending users of
         * this task group to leave their RCU critical section to ensure no new
         * user will see our dying task group any more. Specifically ensure
         * that tg_unthrottle_up() won't add decayed cfs_rq's to it.
         *
         * We therefore defer calling unregister_fair_sched_group() to
         * sched_unregister_group() which is guarantied to get called only after the
         * current RCU grace period has expired.
         */
        spin_lock_irqsave(&task_group_lock, flags);
        list_del_rcu(&tg->list);
        list_del_rcu(&tg->siblings);
        spin_unlock_irqrestore(&task_group_lock, flags);
}

static void sched_change_group(struct task_struct *tsk, int type)
{
        struct task_group *tg;

        /*
         * All callers are synchronized by task_rq_lock(); we do not use RCU
         * which is pointless here. Thus, we pass "true" to task_css_check()
         * to prevent lockdep warnings.
         */
        tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),
                          struct task_group, css);
        tg = autogroup_task_group(tsk, tg);
        tsk->sched_task_group = tg;

#ifdef CONFIG_FAIR_GROUP_SCHED
        if (tsk->sched_class->task_change_group)
                tsk->sched_class->task_change_group(tsk, type);
        else
#endif
                set_task_rq(tsk, task_cpu(tsk));
}

/*
 * Change task's runqueue when it moves between groups.
 *
 * The caller of this function should have put the task in its new group by
 * now. This function just updates tsk->se.cfs_rq and tsk->se.parent to reflect
 * its new group.
 */
void sched_move_task(struct task_struct *tsk)
{
        int queued, running, queue_flags =
                DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(tsk, &rf);
        update_rq_clock(rq);

        running = task_current(rq, tsk);
        queued = task_on_rq_queued(tsk);

        if (queued)
                dequeue_task(rq, tsk, queue_flags);
        if (running)
                put_prev_task(rq, tsk);

        sched_change_group(tsk, TASK_MOVE_GROUP);

        if (queued)
                enqueue_task(rq, tsk, queue_flags);
        if (running) {
                set_next_task(rq, tsk);
                /*
                 * After changing group, the running task may have joined a
                 * throttled one but it's still the running task. Trigger a
                 * resched to make sure that task can still run.
                 */
                resched_curr(rq);
        }

        task_rq_unlock(rq, tsk, &rf);
}

static inline struct task_group *css_tg(struct cgroup_subsys_state *css)
{
        return css ? container_of(css, struct task_group, css) : NULL;
}

static struct cgroup_subsys_state *
cpu_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
{
        struct task_group *parent = css_tg(parent_css);
        struct task_group *tg;

        if (!parent) {
                /* This is early initialization for the top cgroup */
                return &root_task_group.css;
        }

        tg = sched_create_group(parent);
        if (IS_ERR(tg))
                return ERR_PTR(-ENOMEM);

        return &tg->css;
}

/* Expose task group only after completing cgroup initialization */
static int cpu_cgroup_css_online(struct cgroup_subsys_state *css)
{
        struct task_group *tg = css_tg(css);
        struct task_group *parent = css_tg(css->parent);

        if (parent)
                sched_online_group(tg, parent);

#ifdef CONFIG_UCLAMP_TASK_GROUP
        /* Propagate the effective uclamp value for the new group */
        mutex_lock(&uclamp_mutex);
        rcu_read_lock();
        cpu_util_update_eff(css);
        rcu_read_unlock();
        mutex_unlock(&uclamp_mutex);
#endif

        return 0;
}

static void cpu_cgroup_css_released(struct cgroup_subsys_state *css)
{
        struct task_group *tg = css_tg(css);

        sched_release_group(tg);
}

static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
{
        struct task_group *tg = css_tg(css);

        /*
         * Relies on the RCU grace period between css_released() and this.
         */
        sched_unregister_group(tg);
}

/*
 * This is called before wake_up_new_task(), therefore we really only
 * have to set its group bits, all the other stuff does not apply.
 */
static void cpu_cgroup_fork(struct task_struct *task)
{
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(task, &rf);

        update_rq_clock(rq);
        sched_change_group(task, TASK_SET_GROUP);

        task_rq_unlock(rq, task, &rf);
}

static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
{
        struct task_struct *task;
        struct cgroup_subsys_state *css;
        int ret = 0;

        cgroup_taskset_for_each(task, css, tset) {
#ifdef CONFIG_RT_GROUP_SCHED
                if (!sched_rt_can_attach(css_tg(css), task))
                        return -EINVAL;
#endif
                /*
                 * Serialize against wake_up_new_task() such that if it's
                 * running, we're sure to observe its full state.
                 */
                raw_spin_lock_irq(&task->pi_lock);
                /*
                 * Avoid calling sched_move_task() before wake_up_new_task()
                 * has happened. This would lead to problems with PELT, due to
                 * move wanting to detach+attach while we're not attached yet.
                 */
                if (READ_ONCE(task->__state) == TASK_NEW)
                        ret = -EINVAL;
                raw_spin_unlock_irq(&task->pi_lock);

                if (ret)
                        break;
        }
        return ret;
}

static void cpu_cgroup_attach(struct cgroup_taskset *tset)
{
        struct task_struct *task;
        struct cgroup_subsys_state *css;

        cgroup_taskset_for_each(task, css, tset)
                sched_move_task(task);
}

#ifdef CONFIG_UCLAMP_TASK_GROUP
static void cpu_util_update_eff(struct cgroup_subsys_state *css)
{
        struct cgroup_subsys_state *top_css = css;
        struct uclamp_se *uc_parent = NULL;
        struct uclamp_se *uc_se = NULL;
        unsigned int eff[UCLAMP_CNT];
        enum uclamp_id clamp_id;
        unsigned int clamps;

        lockdep_assert_held(&uclamp_mutex);
        SCHED_WARN_ON(!rcu_read_lock_held());

        css_for_each_descendant_pre(css, top_css) {
                uc_parent = css_tg(css)->parent
                        ? css_tg(css)->parent->uclamp : NULL;

                for_each_clamp_id(clamp_id) {
                        /* Assume effective clamps matches requested clamps */
                        eff[clamp_id] = css_tg(css)->uclamp_req[clamp_id].value;
                        /* Cap effective clamps with parent's effective clamps */
                        if (uc_parent &&
                            eff[clamp_id] > uc_parent[clamp_id].value) {
                                eff[clamp_id] = uc_parent[clamp_id].value;
                        }
                }
                /* Ensure protection is always capped by limit */
                eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]);

                /* Propagate most restrictive effective clamps */
                clamps = 0x0;
                uc_se = css_tg(css)->uclamp;
                for_each_clamp_id(clamp_id) {
                        if (eff[clamp_id] == uc_se[clamp_id].value)
                                continue;
                        uc_se[clamp_id].value = eff[clamp_id];
                        uc_se[clamp_id].bucket_id = uclamp_bucket_id(eff[clamp_id]);
                        clamps |= (0x1 << clamp_id);
                }
                if (!clamps) {
                        css = css_rightmost_descendant(css);
                        continue;
                }

                /* Immediately update descendants RUNNABLE tasks */
                uclamp_update_active_tasks(css);
        }
}

/*
 * Integer 10^N with a given N exponent by casting to integer the literal "1eN"
 * C expression. Since there is no way to convert a macro argument (N) into a
 * character constant, use two levels of macros.
 */
#define _POW10(exp) ((unsigned int)1e##exp)
#define POW10(exp) _POW10(exp)

struct uclamp_request {
#define UCLAMP_PERCENT_SHIFT    2
#define UCLAMP_PERCENT_SCALE    (100 * POW10(UCLAMP_PERCENT_SHIFT))
        s64 percent;
        u64 util;
        int ret;
};

static inline struct uclamp_request
capacity_from_percent(char *buf)
{
        struct uclamp_request req = {
                .percent = UCLAMP_PERCENT_SCALE,
                .util = SCHED_CAPACITY_SCALE,
                .ret = 0,
        };

        buf = strim(buf);
        if (strcmp(buf, "max")) {
                req.ret = cgroup_parse_float(buf, UCLAMP_PERCENT_SHIFT,
                                             &req.percent);
                if (req.ret)
                        return req;
                if ((u64)req.percent > UCLAMP_PERCENT_SCALE) {
                        req.ret = -ERANGE;
                        return req;
                }

                req.util = req.percent << SCHED_CAPACITY_SHIFT;
                req.util = DIV_ROUND_CLOSEST_ULL(req.util, UCLAMP_PERCENT_SCALE);
        }

        return req;
}

static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
                                size_t nbytes, loff_t off,
                                enum uclamp_id clamp_id)
{
        struct uclamp_request req;
        struct task_group *tg;

        req = capacity_from_percent(buf);
        if (req.ret)
                return req.ret;

        static_branch_enable(&sched_uclamp_used);

        mutex_lock(&uclamp_mutex);
        rcu_read_lock();

        tg = css_tg(of_css(of));
        if (tg->uclamp_req[clamp_id].value != req.util)
                uclamp_se_set(&tg->uclamp_req[clamp_id], req.util, false);

        /*
         * Because of not recoverable conversion rounding we keep track of the
         * exact requested value
         */
        tg->uclamp_pct[clamp_id] = req.percent;

        /* Update effective clamps to track the most restrictive value */
        cpu_util_update_eff(of_css(of));

        rcu_read_unlock();
        mutex_unlock(&uclamp_mutex);

        return nbytes;
}

static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
                                    char *buf, size_t nbytes,
                                    loff_t off)
{
        return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MIN);
}

static ssize_t cpu_uclamp_max_write(struct kernfs_open_file *of,
                                    char *buf, size_t nbytes,
                                    loff_t off)
{
        return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MAX);
}

static inline void cpu_uclamp_print(struct seq_file *sf,
                                    enum uclamp_id clamp_id)
{
        struct task_group *tg;
        u64 util_clamp;
        u64 percent;
        u32 rem;

        rcu_read_lock();
        tg = css_tg(seq_css(sf));
        util_clamp = tg->uclamp_req[clamp_id].value;
        rcu_read_unlock();

        if (util_clamp == SCHED_CAPACITY_SCALE) {
                seq_puts(sf, "max\n");
                return;
        }

        percent = tg->uclamp_pct[clamp_id];
        percent = div_u64_rem(percent, POW10(UCLAMP_PERCENT_SHIFT), &rem);
        seq_printf(sf, "%llu.%0*u\n", percent, UCLAMP_PERCENT_SHIFT, rem);
}

static int cpu_uclamp_min_show(struct seq_file *sf, void *v)
{
        cpu_uclamp_print(sf, UCLAMP_MIN);
        return 0;
}

static int cpu_uclamp_max_show(struct seq_file *sf, void *v)
{
        cpu_uclamp_print(sf, UCLAMP_MAX);
        return 0;
}
#endif /* CONFIG_UCLAMP_TASK_GROUP */

#ifdef CONFIG_FAIR_GROUP_SCHED
static int cpu_shares_write_u64(struct cgroup_subsys_state *css,
                                struct cftype *cftype, u64 shareval)
{
        if (shareval > scale_load_down(ULONG_MAX))
                shareval = MAX_SHARES;
        return sched_group_set_shares(css_tg(css), scale_load(shareval));
}

static u64 cpu_shares_read_u64(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        struct task_group *tg = css_tg(css);

        return (u64) scale_load_down(tg->shares);
}

#ifdef CONFIG_CFS_BANDWIDTH
static DEFINE_MUTEX(cfs_constraints_mutex);

const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */
static const u64 min_cfs_quota_period = 1 * NSEC_PER_MSEC; /* 1ms */
/* More than 203 days if BW_SHIFT equals 20. */
static const u64 max_cfs_runtime = MAX_BW * NSEC_PER_USEC;

static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime);

static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
                                u64 burst)
{
        int i, ret = 0, runtime_enabled, runtime_was_enabled;
        struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;

        if (tg == &root_task_group)
                return -EINVAL;

        /*
         * Ensure we have at some amount of bandwidth every period.  This is
         * to prevent reaching a state of large arrears when throttled via
         * entity_tick() resulting in prolonged exit starvation.
         */
        if (quota < min_cfs_quota_period || period < min_cfs_quota_period)
                return -EINVAL;

        /*
         * Likewise, bound things on the other side by preventing insane quota
         * periods.  This also allows us to normalize in computing quota
         * feasibility.
         */
        if (period > max_cfs_quota_period)
                return -EINVAL;

        /*
         * Bound quota to defend quota against overflow during bandwidth shift.
         */
        if (quota != RUNTIME_INF && quota > max_cfs_runtime)
                return -EINVAL;

        if (quota != RUNTIME_INF && (burst > quota ||
                                     burst + quota > max_cfs_runtime))
                return -EINVAL;

        /*
         * Prevent race between setting of cfs_rq->runtime_enabled and
         * unthrottle_offline_cfs_rqs().
         */
        cpus_read_lock();
        mutex_lock(&cfs_constraints_mutex);
        ret = __cfs_schedulable(tg, period, quota);
        if (ret)
                goto out_unlock;

        runtime_enabled = quota != RUNTIME_INF;
        runtime_was_enabled = cfs_b->quota != RUNTIME_INF;
        /*
         * If we need to toggle cfs_bandwidth_used, off->on must occur
         * before making related changes, and on->off must occur afterwards
         */
        if (runtime_enabled && !runtime_was_enabled)
                cfs_bandwidth_usage_inc();
        raw_spin_lock_irq(&cfs_b->lock);
        cfs_b->period = ns_to_ktime(period);
        cfs_b->quota = quota;
        cfs_b->burst = burst;

        __refill_cfs_bandwidth_runtime(cfs_b);

        /* Restart the period timer (if active) to handle new period expiry: */
        if (runtime_enabled)
                start_cfs_bandwidth(cfs_b);

        raw_spin_unlock_irq(&cfs_b->lock);

        for_each_online_cpu(i) {
                struct cfs_rq *cfs_rq = tg->cfs_rq[i];
                struct rq *rq = cfs_rq->rq;
                struct rq_flags rf;

                rq_lock_irq(rq, &rf);
                cfs_rq->runtime_enabled = runtime_enabled;
                cfs_rq->runtime_remaining = 0;

                if (cfs_rq->throttled)
                        unthrottle_cfs_rq(cfs_rq);
                rq_unlock_irq(rq, &rf);
        }
        if (runtime_was_enabled && !runtime_enabled)
                cfs_bandwidth_usage_dec();
out_unlock:
        mutex_unlock(&cfs_constraints_mutex);
        cpus_read_unlock();

        return ret;
}

static int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)
{
        u64 quota, period, burst;

        period = ktime_to_ns(tg->cfs_bandwidth.period);
        burst = tg->cfs_bandwidth.burst;
        if (cfs_quota_us < 0)
                quota = RUNTIME_INF;
        else if ((u64)cfs_quota_us <= U64_MAX / NSEC_PER_USEC)
                quota = (u64)cfs_quota_us * NSEC_PER_USEC;
        else
                return -EINVAL;

        return tg_set_cfs_bandwidth(tg, period, quota, burst);
}

static long tg_get_cfs_quota(struct task_group *tg)
{
        u64 quota_us;

        if (tg->cfs_bandwidth.quota == RUNTIME_INF)
                return -1;

        quota_us = tg->cfs_bandwidth.quota;
        do_div(quota_us, NSEC_PER_USEC);

        return quota_us;
}

static int tg_set_cfs_period(struct task_group *tg, long cfs_period_us)
{
        u64 quota, period, burst;

        if ((u64)cfs_period_us > U64_MAX / NSEC_PER_USEC)
                return -EINVAL;

        period = (u64)cfs_period_us * NSEC_PER_USEC;
        quota = tg->cfs_bandwidth.quota;
        burst = tg->cfs_bandwidth.burst;

        return tg_set_cfs_bandwidth(tg, period, quota, burst);
}

static long tg_get_cfs_period(struct task_group *tg)
{
        u64 cfs_period_us;

        cfs_period_us = ktime_to_ns(tg->cfs_bandwidth.period);
        do_div(cfs_period_us, NSEC_PER_USEC);

        return cfs_period_us;
}

static int tg_set_cfs_burst(struct task_group *tg, long cfs_burst_us)
{
        u64 quota, period, burst;

        if ((u64)cfs_burst_us > U64_MAX / NSEC_PER_USEC)
                return -EINVAL;

        burst = (u64)cfs_burst_us * NSEC_PER_USEC;
        period = ktime_to_ns(tg->cfs_bandwidth.period);
        quota = tg->cfs_bandwidth.quota;

        return tg_set_cfs_bandwidth(tg, period, quota, burst);
}

static long tg_get_cfs_burst(struct task_group *tg)
{
        u64 burst_us;

        burst_us = tg->cfs_bandwidth.burst;
        do_div(burst_us, NSEC_PER_USEC);

        return burst_us;
}

static s64 cpu_cfs_quota_read_s64(struct cgroup_subsys_state *css,
                                  struct cftype *cft)
{
        return tg_get_cfs_quota(css_tg(css));
}

static int cpu_cfs_quota_write_s64(struct cgroup_subsys_state *css,
                                   struct cftype *cftype, s64 cfs_quota_us)
{
        return tg_set_cfs_quota(css_tg(css), cfs_quota_us);
}

static u64 cpu_cfs_period_read_u64(struct cgroup_subsys_state *css,
                                   struct cftype *cft)
{
        return tg_get_cfs_period(css_tg(css));
}

static int cpu_cfs_period_write_u64(struct cgroup_subsys_state *css,
                                    struct cftype *cftype, u64 cfs_period_us)
{
        return tg_set_cfs_period(css_tg(css), cfs_period_us);
}

static u64 cpu_cfs_burst_read_u64(struct cgroup_subsys_state *css,
                                  struct cftype *cft)
{
        return tg_get_cfs_burst(css_tg(css));
}

static int cpu_cfs_burst_write_u64(struct cgroup_subsys_state *css,
                                   struct cftype *cftype, u64 cfs_burst_us)
{
        return tg_set_cfs_burst(css_tg(css), cfs_burst_us);
}

struct cfs_schedulable_data {
        struct task_group *tg;
        u64 period, quota;
};

/*
 * normalize group quota/period to be quota/max_period
 * note: units are usecs
 */
static u64 normalize_cfs_quota(struct task_group *tg,
                               struct cfs_schedulable_data *d)
{
        u64 quota, period;

        if (tg == d->tg) {
                period = d->period;
                quota = d->quota;
        } else {
                period = tg_get_cfs_period(tg);
                quota = tg_get_cfs_quota(tg);
        }

        /* note: these should typically be equivalent */
        if (quota == RUNTIME_INF || quota == -1)
                return RUNTIME_INF;

        return to_ratio(period, quota);
}

static int tg_cfs_schedulable_down(struct task_group *tg, void *data)
{
        struct cfs_schedulable_data *d = data;
        struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
        s64 quota = 0, parent_quota = -1;

        if (!tg->parent) {
                quota = RUNTIME_INF;
        } else {
                struct cfs_bandwidth *parent_b = &tg->parent->cfs_bandwidth;

                quota = normalize_cfs_quota(tg, d);
                parent_quota = parent_b->hierarchical_quota;

                /*
                 * Ensure max(child_quota) <= parent_quota.  On cgroup2,
                 * always take the min.  On cgroup1, only inherit when no
                 * limit is set:
                 */
                if (cgroup_subsys_on_dfl(cpu_cgrp_subsys)) {
                        quota = min(quota, parent_quota);
                } else {
                        if (quota == RUNTIME_INF)
                                quota = parent_quota;
                        else if (parent_quota != RUNTIME_INF && quota > parent_quota)
                                return -EINVAL;
                }
        }
        cfs_b->hierarchical_quota = quota;

        return 0;
}

static int __cfs_schedulable(struct task_group *tg, u64 period, u64 quota)
{
        int ret;
        struct cfs_schedulable_data data = {
                .tg = tg,
                .period = period,
                .quota = quota,
        };

        if (quota != RUNTIME_INF) {
                do_div(data.period, NSEC_PER_USEC);
                do_div(data.quota, NSEC_PER_USEC);
        }

        rcu_read_lock();
        ret = walk_tg_tree(tg_cfs_schedulable_down, tg_nop, &data);
        rcu_read_unlock();

        return ret;
}

static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
{
        struct task_group *tg = css_tg(seq_css(sf));
        struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;

        seq_printf(sf, "nr_periods %d\n", cfs_b->nr_periods);
        seq_printf(sf, "nr_throttled %d\n", cfs_b->nr_throttled);
        seq_printf(sf, "throttled_time %llu\n", cfs_b->throttled_time);

        if (schedstat_enabled() && tg != &root_task_group) {
                u64 ws = 0;
                int i;

                for_each_possible_cpu(i)
                        ws += schedstat_val(tg->se[i]->statistics.wait_sum);

                seq_printf(sf, "wait_sum %llu\n", ws);
        }

        return 0;
}
#endif /* CONFIG_CFS_BANDWIDTH */
#endif /* CONFIG_FAIR_GROUP_SCHED */

#ifdef CONFIG_RT_GROUP_SCHED
static int cpu_rt_runtime_write(struct cgroup_subsys_state *css,
                                struct cftype *cft, s64 val)
{
        return sched_group_set_rt_runtime(css_tg(css), val);
}

static s64 cpu_rt_runtime_read(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        return sched_group_rt_runtime(css_tg(css));
}

static int cpu_rt_period_write_uint(struct cgroup_subsys_state *css,
                                    struct cftype *cftype, u64 rt_period_us)
{
        return sched_group_set_rt_period(css_tg(css), rt_period_us);
}

static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
                                   struct cftype *cft)
{
        return sched_group_rt_period(css_tg(css));
}
#endif /* CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_FAIR_GROUP_SCHED
static s64 cpu_idle_read_s64(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        return css_tg(css)->idle;
}

static int cpu_idle_write_s64(struct cgroup_subsys_state *css,
                                struct cftype *cft, s64 idle)
{
        return sched_group_set_idle(css_tg(css), idle);
}
#endif

static struct cftype cpu_legacy_files[] = {
#ifdef CONFIG_FAIR_GROUP_SCHED
        {
                .name = "shares",
                .read_u64 = cpu_shares_read_u64,
                .write_u64 = cpu_shares_write_u64,
        },
        {
                .name = "idle",
                .read_s64 = cpu_idle_read_s64,
                .write_s64 = cpu_idle_write_s64,
        },
#endif
#ifdef CONFIG_CFS_BANDWIDTH
        {
                .name = "cfs_quota_us",
                .read_s64 = cpu_cfs_quota_read_s64,
                .write_s64 = cpu_cfs_quota_write_s64,
        },
        {
                .name = "cfs_period_us",
                .read_u64 = cpu_cfs_period_read_u64,
                .write_u64 = cpu_cfs_period_write_u64,
        },
        {
                .name = "cfs_burst_us",
                .read_u64 = cpu_cfs_burst_read_u64,
                .write_u64 = cpu_cfs_burst_write_u64,
        },
        {
                .name = "stat",
                .seq_show = cpu_cfs_stat_show,
        },
#endif
#ifdef CONFIG_RT_GROUP_SCHED
        {
                .name = "rt_runtime_us",
                .read_s64 = cpu_rt_runtime_read,
                .write_s64 = cpu_rt_runtime_write,
        },
        {
                .name = "rt_period_us",
                .read_u64 = cpu_rt_period_read_uint,
                .write_u64 = cpu_rt_period_write_uint,
        },
#endif
#ifdef CONFIG_UCLAMP_TASK_GROUP
        {
                .name = "uclamp.min",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_uclamp_min_show,
                .write = cpu_uclamp_min_write,
        },
        {
                .name = "uclamp.max",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_uclamp_max_show,
                .write = cpu_uclamp_max_write,
        },
#endif
        { }     /* Terminate */
};

static int cpu_extra_stat_show(struct seq_file *sf,
                               struct cgroup_subsys_state *css)
{
#ifdef CONFIG_CFS_BANDWIDTH
        {
                struct task_group *tg = css_tg(css);
                struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
                u64 throttled_usec;

                throttled_usec = cfs_b->throttled_time;
                do_div(throttled_usec, NSEC_PER_USEC);

                seq_printf(sf, "nr_periods %d\n"
                           "nr_throttled %d\n"
                           "throttled_usec %llu\n",
                           cfs_b->nr_periods, cfs_b->nr_throttled,
                           throttled_usec);
        }
#endif
        return 0;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static u64 cpu_weight_read_u64(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        struct task_group *tg = css_tg(css);
        u64 weight = scale_load_down(tg->shares);

        return DIV_ROUND_CLOSEST_ULL(weight * CGROUP_WEIGHT_DFL, 1024);
}

static int cpu_weight_write_u64(struct cgroup_subsys_state *css,
                                struct cftype *cft, u64 weight)
{
        /*
         * cgroup weight knobs should use the common MIN, DFL and MAX
         * values which are 1, 100 and 10000 respectively.  While it loses
         * a bit of range on both ends, it maps pretty well onto the shares
         * value used by scheduler and the round-trip conversions preserve
         * the original value over the entire range.
         */
        if (weight < CGROUP_WEIGHT_MIN || weight > CGROUP_WEIGHT_MAX)
                return -ERANGE;

        weight = DIV_ROUND_CLOSEST_ULL(weight * 1024, CGROUP_WEIGHT_DFL);

        return sched_group_set_shares(css_tg(css), scale_load(weight));
}

static s64 cpu_weight_nice_read_s64(struct cgroup_subsys_state *css,
                                    struct cftype *cft)
{
        unsigned long weight = scale_load_down(css_tg(css)->shares);
        int last_delta = INT_MAX;
        int prio, delta;

        /* find the closest nice value to the current weight */
        for (prio = 0; prio < ARRAY_SIZE(sched_prio_to_weight); prio++) {
                delta = abs(sched_prio_to_weight[prio] - weight);
                if (delta >= last_delta)
                        break;
                last_delta = delta;
        }

        return PRIO_TO_NICE(prio - 1 + MAX_RT_PRIO);
}

static int cpu_weight_nice_write_s64(struct cgroup_subsys_state *css,
                                     struct cftype *cft, s64 nice)
{
        unsigned long weight;
        int idx;

        if (nice < MIN_NICE || nice > MAX_NICE)
                return -ERANGE;

        idx = NICE_TO_PRIO(nice) - MAX_RT_PRIO;
        idx = array_index_nospec(idx, 40);
        weight = sched_prio_to_weight[idx];

        return sched_group_set_shares(css_tg(css), scale_load(weight));
}
#endif

static void __maybe_unused cpu_period_quota_print(struct seq_file *sf,
                                                  long period, long quota)
{
        if (quota < 0)
                seq_puts(sf, "max");
        else
                seq_printf(sf, "%ld", quota);

        seq_printf(sf, " %ld\n", period);
}

/* caller should put the current value in *@periodp before calling */
static int __maybe_unused cpu_period_quota_parse(char *buf,
                                                 u64 *periodp, u64 *quotap)
{
        char tok[21];   /* U64_MAX */

        if (sscanf(buf, "%20s %llu", tok, periodp) < 1)
                return -EINVAL;

        *periodp *= NSEC_PER_USEC;

        if (sscanf(tok, "%llu", quotap))
                *quotap *= NSEC_PER_USEC;
        else if (!strcmp(tok, "max"))
                *quotap = RUNTIME_INF;
        else
                return -EINVAL;

        return 0;
}

#ifdef CONFIG_CFS_BANDWIDTH
static int cpu_max_show(struct seq_file *sf, void *v)
{
        struct task_group *tg = css_tg(seq_css(sf));

        cpu_period_quota_print(sf, tg_get_cfs_period(tg), tg_get_cfs_quota(tg));
        return 0;
}

static ssize_t cpu_max_write(struct kernfs_open_file *of,
                             char *buf, size_t nbytes, loff_t off)
{
        struct task_group *tg = css_tg(of_css(of));
        u64 period = tg_get_cfs_period(tg);
        u64 burst = tg_get_cfs_burst(tg);
        u64 quota;
        int ret;

        ret = cpu_period_quota_parse(buf, &period, &quota);
        if (!ret)
                ret = tg_set_cfs_bandwidth(tg, period, quota, burst);
        return ret ?: nbytes;
}
#endif

static struct cftype cpu_files[] = {
#ifdef CONFIG_FAIR_GROUP_SCHED
        {
                .name = "weight",
                .flags = CFTYPE_NOT_ON_ROOT,
                .read_u64 = cpu_weight_read_u64,
                .write_u64 = cpu_weight_write_u64,
        },
        {
                .name = "weight.nice",
                .flags = CFTYPE_NOT_ON_ROOT,
                .read_s64 = cpu_weight_nice_read_s64,
                .write_s64 = cpu_weight_nice_write_s64,
        },
        {
                .name = "idle",
                .flags = CFTYPE_NOT_ON_ROOT,
                .read_s64 = cpu_idle_read_s64,
                .write_s64 = cpu_idle_write_s64,
        },
#endif
#ifdef CONFIG_CFS_BANDWIDTH
        {
                .name = "max",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_max_show,
                .write = cpu_max_write,
        },
        {
                .name = "max.burst",
                .flags = CFTYPE_NOT_ON_ROOT,
                .read_u64 = cpu_cfs_burst_read_u64,
                .write_u64 = cpu_cfs_burst_write_u64,
        },
#endif
#ifdef CONFIG_UCLAMP_TASK_GROUP
        {
                .name = "uclamp.min",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_uclamp_min_show,
                .write = cpu_uclamp_min_write,
        },
        {
                .name = "uclamp.max",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_uclamp_max_show,
                .write = cpu_uclamp_max_write,
        },
#endif
        { }     /* terminate */
};

struct cgroup_subsys cpu_cgrp_subsys = {
        .css_alloc      = cpu_cgroup_css_alloc,
        .css_online     = cpu_cgroup_css_online,
        .css_released   = cpu_cgroup_css_released,
        .css_free       = cpu_cgroup_css_free,
        .css_extra_stat_show = cpu_extra_stat_show,
        .fork           = cpu_cgroup_fork,
        .can_attach     = cpu_cgroup_can_attach,
        .attach         = cpu_cgroup_attach,
        .legacy_cftypes = cpu_legacy_files,
        .dfl_cftypes    = cpu_files,
        .early_init     = true,
        .threaded       = true,
};

#endif  /* CONFIG_CGROUP_SCHED */

void dump_cpu_task(int cpu)
{
        pr_info("Task dump for CPU %d:\n", cpu);
        sched_show_task(cpu_curr(cpu));
}

/*
 * Nice levels are multiplicative, with a gentle 10% change for every
 * nice level changed. I.e. when a CPU-bound task goes from nice 0 to
 * nice 1, it will get ~10% less CPU time than another CPU-bound task
 * that remained on nice 0.
 *
 * The "10% effect" is relative and cumulative: from _any_ nice level,
 * if you go up 1 level, it's -10% CPU usage, if you go down 1 level
 * it's +10% CPU usage. (to achieve that we use a multiplier of 1.25.
 * If a task goes up by ~10% and another task goes down by ~10% then
 * the relative distance between them is ~25%.)
 */
const int sched_prio_to_weight[40] = {
 /* -20 */     88761,     71755,     56483,     46273,     36291,
 /* -15 */     29154,     23254,     18705,     14949,     11916,
 /* -10 */      9548,      7620,      6100,      4904,      3906,
 /*  -5 */      3121,      2501,      1991,      1586,      1277,
 /*   0 */      1024,       820,       655,       526,       423,
 /*   5 */       335,       272,       215,       172,       137,
 /*  10 */       110,        87,        70,        56,        45,
 /*  15 */        36,        29,        23,        18,        15,
};

/*
 * Inverse (2^32/x) values of the sched_prio_to_weight[] array, precalculated.
 *
 * In cases where the weight does not change often, we can use the
 * precalculated inverse to speed up arithmetics by turning divisions
 * into multiplications:
 */
const u32 sched_prio_to_wmult[40] = {
 /* -20 */     48388,     59856,     76040,     92818,    118348,
 /* -15 */    147320,    184698,    229616,    287308,    360437,
 /* -10 */    449829,    563644,    704093,    875809,   1099582,
 /*  -5 */   1376151,   1717300,   2157191,   2708050,   3363326,
 /*   0 */   4194304,   5237765,   6557202,   8165337,  10153587,
 /*   5 */  12820798,  15790321,  19976592,  24970740,  31350126,
 /*  10 */  39045157,  49367440,  61356676,  76695844,  95443717,
 /*  15 */ 119304647, 148102320, 186737708, 238609294, 286331153,
};

void call_trace_sched_update_nr_running(struct rq *rq, int count)
{
        trace_sched_update_nr_running_tp(rq, count);
}