sched,lockdep: Employ lock pinning

Employ the new lockdep lock pinning annotation to ensure no
'accidental' lock-breaks happen with rq->lock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: ktkhai@parallels.com
Cc: rostedt@goodmis.org
Cc: juri.lelli@gmail.com
Cc: pang.xunlei@linaro.org
Cc: oleg@redhat.com
Cc: wanpeng.li@linux.intel.com
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20150611124744.003233193@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1ddc129..c74191a 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1201,8 +1201,15 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
                stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
                tlb_migrate_finish(p->mm);
                return 0;
-       } else if (task_on_rq_queued(p))
+       } else if (task_on_rq_queued(p)) {
+               /*
+                * OK, since we're going to drop the lock immediately
+                * afterwards anyway.
+                */
+               lockdep_unpin_lock(&rq->lock);
                rq = move_queued_task(rq, p, dest_cpu);
+               lockdep_pin_lock(&rq->lock);
+       }
 out:
        task_rq_unlock(rq, p, &flags);
 
@@ -1562,6 +1569,8 @@ out:
 static inline
 int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags)
 {
+       lockdep_assert_held(&p->pi_lock);
+
        if (p->nr_cpus_allowed > 1)
                cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags);
 
@@ -1652,9 +1661,12 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 #ifdef CONFIG_SMP
        if (p->sched_class->task_woken) {
                /*
-                * XXX can drop rq->lock; most likely ok.
+                * Our task @p is fully woken up and running; so its safe to
+                * drop the rq->lock, hereafter rq is only used for statistics.
                 */
+               lockdep_unpin_lock(&rq->lock);
                p->sched_class->task_woken(rq, p);
+               lockdep_pin_lock(&rq->lock);
        }
 
        if (rq->idle_stamp) {
@@ -1674,6 +1686,8 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 static void
 ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags)
 {
+       lockdep_assert_held(&rq->lock);
+
 #ifdef CONFIG_SMP
        if (p->sched_contributes_to_load)
                rq->nr_uninterruptible--;
@@ -1718,6 +1732,7 @@ void sched_ttwu_pending(void)
                return;
 
        raw_spin_lock_irqsave(&rq->lock, flags);
+       lockdep_pin_lock(&rq->lock);
 
        while (llist) {
                p = llist_entry(llist, struct task_struct, wake_entry);
@@ -1725,6 +1740,7 @@ void sched_ttwu_pending(void)
                ttwu_do_activate(rq, p, 0);
        }
 
+       lockdep_unpin_lock(&rq->lock);
        raw_spin_unlock_irqrestore(&rq->lock, flags);
 }
 
@@ -1821,7 +1837,9 @@ static void ttwu_queue(struct task_struct *p, int cpu)
 #endif
 
        raw_spin_lock(&rq->lock);
+       lockdep_pin_lock(&rq->lock);
        ttwu_do_activate(rq, p, 0);
+       lockdep_unpin_lock(&rq->lock);
        raw_spin_unlock(&rq->lock);
 }
 
@@ -1916,9 +1934,17 @@ static void try_to_wake_up_local(struct task_struct *p)
        lockdep_assert_held(&rq->lock);
 
        if (!raw_spin_trylock(&p->pi_lock)) {
+               /*
+                * This is OK, because current is on_cpu, which avoids it being
+                * picked for load-balance and preemption/IRQs are still
+                * disabled avoiding further scheduler activity on it and we've
+                * not yet picked a replacement task.
+                */
+               lockdep_unpin_lock(&rq->lock);
                raw_spin_unlock(&rq->lock);
                raw_spin_lock(&p->pi_lock);
                raw_spin_lock(&rq->lock);
+               lockdep_pin_lock(&rq->lock);
        }
 
        if (!(p->state & TASK_NORMAL))
@@ -2530,6 +2556,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
         * of the scheduler it's an obvious special-case), so we
         * do an early lockdep release here:
         */
+       lockdep_unpin_lock(&rq->lock);
        spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
 
        context_tracking_task_switch(prev, next);
@@ -2953,6 +2980,7 @@ static void __sched __schedule(void)
         */
        smp_mb__before_spinlock();
        raw_spin_lock_irq(&rq->lock);
+       lockdep_pin_lock(&rq->lock);
 
        rq->clock_skip_update <<= 1; /* promote REQ to ACT */
 
@@ -2995,8 +3023,10 @@ static void __sched __schedule(void)
 
                rq = context_switch(rq, prev, next); /* unlocks the rq */
                cpu = cpu_of(rq);
-       } else
+       } else {
+               lockdep_unpin_lock(&rq->lock);
                raw_spin_unlock_irq(&rq->lock);
+       }
 
        balance_callback(rq);
 }
@@ -5065,6 +5095,11 @@ static void migrate_tasks(struct rq *dead_rq)
                if (rq->nr_running == 1)
                        break;
 
+               /*
+                * Ensure rq->lock covers the entire task selection
+                * until the migration.
+                */
+               lockdep_pin_lock(&rq->lock);
                next = pick_next_task(rq, &fake_task);
                BUG_ON(!next);
                next->sched_class->put_prev_task(rq, next);
@@ -5072,6 +5107,7 @@ static void migrate_tasks(struct rq *dead_rq)
                /* Find suitable destination for @next, with force if needed. */
                dest_cpu = select_fallback_rq(dead_rq->cpu, next);
 
+               lockdep_unpin_lock(&rq->lock);
                rq = __migrate_task(rq, next, dest_cpu);
                if (rq != dead_rq) {
                        raw_spin_unlock(&rq->lock);

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 6318f43..e814641 100644 (file)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1151,7 +1151,15 @@ struct task_struct *pick_next_task_dl(struct rq *rq, struct task_struct *prev)
        dl_rq = &rq->dl;
 
        if (need_pull_dl_task(rq, prev)) {
+               /*
+                * This is OK, because current is on_cpu, which avoids it being
+                * picked for load-balance and preemption/IRQs are still
+                * disabled avoiding further scheduler activity on it and we're
+                * being very careful to re-start the picking loop.
+                */
+               lockdep_unpin_lock(&rq->lock);
                pull_dl_task(rq);
+               lockdep_pin_lock(&rq->lock);
                /*
                 * pull_rt_task() can drop (and re-acquire) rq->lock; this
                 * means a stop task can slip in, in which case we need to

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7210ae8..509ef63 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5392,7 +5392,15 @@ simple:
        return p;
 
 idle:
+       /*
+        * This is OK, because current is on_cpu, which avoids it being picked
+        * for load-balance and preemption/IRQs are still disabled avoiding
+        * further scheduler activity on it and we're being very careful to
+        * re-start the picking loop.
+        */
+       lockdep_unpin_lock(&rq->lock);
        new_tasks = idle_balance(rq);
+       lockdep_pin_lock(&rq->lock);
        /*
         * Because idle_balance() releases (and re-acquires) rq->lock, it is
         * possible for any higher priority task to appear. In that case we
@@ -7426,9 +7434,6 @@ static int idle_balance(struct rq *this_rq)
                goto out;
        }
 
-       /*
-        * Drop the rq->lock, but keep IRQ/preempt disabled.
-        */
        raw_spin_unlock(&this_rq->lock);
 
        update_blocked_averages(this_cpu);

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 460f858..0d193a2 100644 (file)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1478,7 +1478,15 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev)
        struct rt_rq *rt_rq = &rq->rt;
 
        if (need_pull_rt_task(rq, prev)) {
+               /*
+                * This is OK, because current is on_cpu, which avoids it being
+                * picked for load-balance and preemption/IRQs are still
+                * disabled avoiding further scheduler activity on it and we're
+                * being very careful to re-start the picking loop.
+                */
+               lockdep_unpin_lock(&rq->lock);
                pull_rt_task(rq);
+               lockdep_pin_lock(&rq->lock);
                /*
                 * pull_rt_task() can drop (and re-acquire) rq->lock; this
                 * means a dl or stop task can slip in, in which case we need

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 62949ab..ef02d11 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1439,8 +1439,10 @@ static inline struct rq *__task_rq_lock(struct task_struct *p)
        for (;;) {
                rq = task_rq(p);
                raw_spin_lock(&rq->lock);
-               if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+               if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
+                       lockdep_pin_lock(&rq->lock);
                        return rq;
+               }
                raw_spin_unlock(&rq->lock);
 
                while (unlikely(task_on_rq_migrating(p)))
@@ -1477,8 +1479,10 @@ static inline struct rq *task_rq_lock(struct task_struct *p, unsigned long *flag
                 * If we observe the new cpu in task_rq_lock, the acquire will
                 * pair with the WMB to ensure we must then also see migrating.
                 */
-               if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+               if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
+                       lockdep_pin_lock(&rq->lock);
                        return rq;
+               }
                raw_spin_unlock(&rq->lock);
                raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
 
@@ -1490,6 +1494,7 @@ static inline struct rq *task_rq_lock(struct task_struct *p, unsigned long *flag
 static inline void __task_rq_unlock(struct rq *rq)
        __releases(rq->lock)
 {
+       lockdep_unpin_lock(&rq->lock);
        raw_spin_unlock(&rq->lock);
 }
 
@@ -1498,6 +1503,7 @@ task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
        __releases(rq->lock)
        __releases(p->pi_lock)
 {
+       lockdep_unpin_lock(&rq->lock);
        raw_spin_unlock(&rq->lock);
        raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
 }