io_uring: reduce scheduling due to tw

[platform/kernel/linux-starfive.git] / io_uring / io_uring.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Shared application/kernel submission and completion ring pairs, for
 * supporting fast/efficient IO.
 *
 * A note on the read/write ordering memory barriers that are matched between
 * the application and kernel side.
 *
 * After the application reads the CQ ring tail, it must use an
 * appropriate smp_rmb() to pair with the smp_wmb() the kernel uses
 * before writing the tail (using smp_load_acquire to read the tail will
 * do). It also needs a smp_mb() before updating CQ head (ordering the
 * entry load(s) with the head store), pairing with an implicit barrier
 * through a control-dependency in io_get_cqe (smp_store_release to
 * store head will do). Failure to do so could lead to reading invalid
 * CQ entries.
 *
 * Likewise, the application must use an appropriate smp_wmb() before
 * writing the SQ tail (ordering SQ entry stores with the tail store),
 * which pairs with smp_load_acquire in io_get_sqring (smp_store_release
 * to store the tail will do). And it needs a barrier ordering the SQ
 * head load before writing new SQ entries (smp_load_acquire to read
 * head will do).
 *
 * When using the SQ poll thread (IORING_SETUP_SQPOLL), the application
 * needs to check the SQ flags for IORING_SQ_NEED_WAKEUP *after*
 * updating the SQ tail; a full memory barrier smp_mb() is needed
 * between.
 *
 * Also see the examples in the liburing library:
 *
 *      git://git.kernel.dk/liburing
 *
 * io_uring also uses READ/WRITE_ONCE() for _any_ store or load that happens
 * from data shared between the kernel and application. This is done both
 * for ordering purposes, but also to ensure that once a value is loaded from
 * data that the application could potentially modify, it remains stable.
 *
 * Copyright (C) 2018-2019 Jens Axboe
 * Copyright (c) 2018-2019 Christoph Hellwig
 */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/syscalls.h>
#include <net/compat.h>
#include <linux/refcount.h>
#include <linux/uio.h>
#include <linux/bits.h>

#include <linux/sched/signal.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/bvec.h>
#include <linux/net.h>
#include <net/sock.h>
#include <net/af_unix.h>
#include <net/scm.h>
#include <linux/anon_inodes.h>
#include <linux/sched/mm.h>
#include <linux/uaccess.h>
#include <linux/nospec.h>
#include <linux/highmem.h>
#include <linux/fsnotify.h>
#include <linux/fadvise.h>
#include <linux/task_work.h>
#include <linux/io_uring.h>
#include <linux/audit.h>
#include <linux/security.h>
#include <asm/shmparam.h>

#define CREATE_TRACE_POINTS
#include <trace/events/io_uring.h>

#include <uapi/linux/io_uring.h>

#include "io-wq.h"

#include "io_uring.h"
#include "opdef.h"
#include "refs.h"
#include "tctx.h"
#include "sqpoll.h"
#include "fdinfo.h"
#include "kbuf.h"
#include "rsrc.h"
#include "cancel.h"
#include "net.h"
#include "notif.h"

#include "timeout.h"
#include "poll.h"
#include "alloc_cache.h"

#define IORING_MAX_ENTRIES      32768
#define IORING_MAX_CQ_ENTRIES   (2 * IORING_MAX_ENTRIES)

#define IORING_MAX_RESTRICTIONS (IORING_RESTRICTION_LAST + \
                                 IORING_REGISTER_LAST + IORING_OP_LAST)

#define SQE_COMMON_FLAGS (IOSQE_FIXED_FILE | IOSQE_IO_LINK | \
                          IOSQE_IO_HARDLINK | IOSQE_ASYNC)

#define SQE_VALID_FLAGS (SQE_COMMON_FLAGS | IOSQE_BUFFER_SELECT | \
                        IOSQE_IO_DRAIN | IOSQE_CQE_SKIP_SUCCESS)

#define IO_REQ_CLEAN_FLAGS (REQ_F_BUFFER_SELECTED | REQ_F_NEED_CLEANUP | \
                                REQ_F_POLLED | REQ_F_INFLIGHT | REQ_F_CREDS | \
                                REQ_F_ASYNC_DATA)

#define IO_REQ_CLEAN_SLOW_FLAGS (REQ_F_REFCOUNT | REQ_F_LINK | REQ_F_HARDLINK |\
                                 IO_REQ_CLEAN_FLAGS)

#define IO_TCTX_REFS_CACHE_NR   (1U << 10)

#define IO_COMPL_BATCH                  32
#define IO_REQ_ALLOC_BATCH              8

enum {
        IO_CHECK_CQ_OVERFLOW_BIT,
        IO_CHECK_CQ_DROPPED_BIT,
};

enum {
        IO_EVENTFD_OP_SIGNAL_BIT,
        IO_EVENTFD_OP_FREE_BIT,
};

struct io_defer_entry {
        struct list_head        list;
        struct io_kiocb         *req;
        u32                     seq;
};

/* requests with any of those set should undergo io_disarm_next() */
#define IO_DISARM_MASK (REQ_F_ARM_LTIMEOUT | REQ_F_LINK_TIMEOUT | REQ_F_FAIL)
#define IO_REQ_LINK_FLAGS (REQ_F_LINK | REQ_F_HARDLINK)

static bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
                                         struct task_struct *task,
                                         bool cancel_all);

static void io_dismantle_req(struct io_kiocb *req);
static void io_clean_op(struct io_kiocb *req);
static void io_queue_sqe(struct io_kiocb *req);
static void io_move_task_work_from_local(struct io_ring_ctx *ctx);
static void __io_submit_flush_completions(struct io_ring_ctx *ctx);
static __cold void io_fallback_tw(struct io_uring_task *tctx);

struct kmem_cache *req_cachep;

struct sock *io_uring_get_socket(struct file *file)
{
#if defined(CONFIG_UNIX)
        if (io_is_uring_fops(file)) {
                struct io_ring_ctx *ctx = file->private_data;

                return ctx->ring_sock->sk;
        }
#endif
        return NULL;
}
EXPORT_SYMBOL(io_uring_get_socket);

static inline void io_submit_flush_completions(struct io_ring_ctx *ctx)
{
        if (!wq_list_empty(&ctx->submit_state.compl_reqs) ||
            ctx->submit_state.cqes_count)
                __io_submit_flush_completions(ctx);
}

static inline unsigned int __io_cqring_events(struct io_ring_ctx *ctx)
{
        return ctx->cached_cq_tail - READ_ONCE(ctx->rings->cq.head);
}

static inline unsigned int __io_cqring_events_user(struct io_ring_ctx *ctx)
{
        return READ_ONCE(ctx->rings->cq.tail) - READ_ONCE(ctx->rings->cq.head);
}

static bool io_match_linked(struct io_kiocb *head)
{
        struct io_kiocb *req;

        io_for_each_link(req, head) {
                if (req->flags & REQ_F_INFLIGHT)
                        return true;
        }
        return false;
}

/*
 * As io_match_task() but protected against racing with linked timeouts.
 * User must not hold timeout_lock.
 */
bool io_match_task_safe(struct io_kiocb *head, struct task_struct *task,
                        bool cancel_all)
{
        bool matched;

        if (task && head->task != task)
                return false;
        if (cancel_all)
                return true;

        if (head->flags & REQ_F_LINK_TIMEOUT) {
                struct io_ring_ctx *ctx = head->ctx;

                /* protect against races with linked timeouts */
                spin_lock_irq(&ctx->timeout_lock);
                matched = io_match_linked(head);
                spin_unlock_irq(&ctx->timeout_lock);
        } else {
                matched = io_match_linked(head);
        }
        return matched;
}

static inline void req_fail_link_node(struct io_kiocb *req, int res)
{
        req_set_fail(req);
        io_req_set_res(req, res, 0);
}

static inline void io_req_add_to_cache(struct io_kiocb *req, struct io_ring_ctx *ctx)
{
        wq_stack_add_head(&req->comp_list, &ctx->submit_state.free_list);
        kasan_poison_object_data(req_cachep, req);
}

static __cold void io_ring_ctx_ref_free(struct percpu_ref *ref)
{
        struct io_ring_ctx *ctx = container_of(ref, struct io_ring_ctx, refs);

        complete(&ctx->ref_comp);
}

static __cold void io_fallback_req_func(struct work_struct *work)
{
        struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx,
                                                fallback_work.work);
        struct llist_node *node = llist_del_all(&ctx->fallback_llist);
        struct io_kiocb *req, *tmp;
        struct io_tw_state ts = { .locked = true, };

        mutex_lock(&ctx->uring_lock);
        llist_for_each_entry_safe(req, tmp, node, io_task_work.node)
                req->io_task_work.func(req, &ts);
        if (WARN_ON_ONCE(!ts.locked))
                return;
        io_submit_flush_completions(ctx);
        mutex_unlock(&ctx->uring_lock);
}

static int io_alloc_hash_table(struct io_hash_table *table, unsigned bits)
{
        unsigned hash_buckets = 1U << bits;
        size_t hash_size = hash_buckets * sizeof(table->hbs[0]);

        table->hbs = kmalloc(hash_size, GFP_KERNEL);
        if (!table->hbs)
                return -ENOMEM;

        table->hash_bits = bits;
        init_hash_table(table, hash_buckets);
        return 0;
}

static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
{
        struct io_ring_ctx *ctx;
        int hash_bits;

        ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
        if (!ctx)
                return NULL;

        xa_init(&ctx->io_bl_xa);

        /*
         * Use 5 bits less than the max cq entries, that should give us around
         * 32 entries per hash list if totally full and uniformly spread, but
         * don't keep too many buckets to not overconsume memory.
         */
        hash_bits = ilog2(p->cq_entries) - 5;
        hash_bits = clamp(hash_bits, 1, 8);
        if (io_alloc_hash_table(&ctx->cancel_table, hash_bits))
                goto err;
        if (io_alloc_hash_table(&ctx->cancel_table_locked, hash_bits))
                goto err;

        ctx->dummy_ubuf = kzalloc(sizeof(*ctx->dummy_ubuf), GFP_KERNEL);
        if (!ctx->dummy_ubuf)
                goto err;
        /* set invalid range, so io_import_fixed() fails meeting it */
        ctx->dummy_ubuf->ubuf = -1UL;

        if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free,
                            0, GFP_KERNEL))
                goto err;

        ctx->flags = p->flags;
        init_waitqueue_head(&ctx->sqo_sq_wait);
        INIT_LIST_HEAD(&ctx->sqd_list);
        INIT_LIST_HEAD(&ctx->cq_overflow_list);
        INIT_LIST_HEAD(&ctx->io_buffers_cache);
        io_alloc_cache_init(&ctx->rsrc_node_cache, IO_NODE_ALLOC_CACHE_MAX,
                            sizeof(struct io_rsrc_node));
        io_alloc_cache_init(&ctx->apoll_cache, IO_ALLOC_CACHE_MAX,
                            sizeof(struct async_poll));
        io_alloc_cache_init(&ctx->netmsg_cache, IO_ALLOC_CACHE_MAX,
                            sizeof(struct io_async_msghdr));
        init_completion(&ctx->ref_comp);
        xa_init_flags(&ctx->personalities, XA_FLAGS_ALLOC1);
        mutex_init(&ctx->uring_lock);
        init_waitqueue_head(&ctx->cq_wait);
        init_waitqueue_head(&ctx->poll_wq);
        spin_lock_init(&ctx->completion_lock);
        spin_lock_init(&ctx->timeout_lock);
        INIT_WQ_LIST(&ctx->iopoll_list);
        INIT_LIST_HEAD(&ctx->io_buffers_pages);
        INIT_LIST_HEAD(&ctx->io_buffers_comp);
        INIT_LIST_HEAD(&ctx->defer_list);
        INIT_LIST_HEAD(&ctx->timeout_list);
        INIT_LIST_HEAD(&ctx->ltimeout_list);
        INIT_LIST_HEAD(&ctx->rsrc_ref_list);
        init_llist_head(&ctx->work_llist);
        INIT_LIST_HEAD(&ctx->tctx_list);
        ctx->submit_state.free_list.next = NULL;
        INIT_WQ_LIST(&ctx->locked_free_list);
        INIT_DELAYED_WORK(&ctx->fallback_work, io_fallback_req_func);
        INIT_WQ_LIST(&ctx->submit_state.compl_reqs);
        return ctx;
err:
        kfree(ctx->dummy_ubuf);
        kfree(ctx->cancel_table.hbs);
        kfree(ctx->cancel_table_locked.hbs);
        kfree(ctx->io_bl);
        xa_destroy(&ctx->io_bl_xa);
        kfree(ctx);
        return NULL;
}

static void io_account_cq_overflow(struct io_ring_ctx *ctx)
{
        struct io_rings *r = ctx->rings;

        WRITE_ONCE(r->cq_overflow, READ_ONCE(r->cq_overflow) + 1);
        ctx->cq_extra--;
}

static bool req_need_defer(struct io_kiocb *req, u32 seq)
{
        if (unlikely(req->flags & REQ_F_IO_DRAIN)) {
                struct io_ring_ctx *ctx = req->ctx;

                return seq + READ_ONCE(ctx->cq_extra) != ctx->cached_cq_tail;
        }

        return false;
}

static inline void io_req_track_inflight(struct io_kiocb *req)
{
        if (!(req->flags & REQ_F_INFLIGHT)) {
                req->flags |= REQ_F_INFLIGHT;
                atomic_inc(&req->task->io_uring->inflight_tracked);
        }
}

static struct io_kiocb *__io_prep_linked_timeout(struct io_kiocb *req)
{
        if (WARN_ON_ONCE(!req->link))
                return NULL;

        req->flags &= ~REQ_F_ARM_LTIMEOUT;
        req->flags |= REQ_F_LINK_TIMEOUT;

        /* linked timeouts should have two refs once prep'ed */
        io_req_set_refcount(req);
        __io_req_set_refcount(req->link, 2);
        return req->link;
}

static inline struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req)
{
        if (likely(!(req->flags & REQ_F_ARM_LTIMEOUT)))
                return NULL;
        return __io_prep_linked_timeout(req);
}

static noinline void __io_arm_ltimeout(struct io_kiocb *req)
{
        io_queue_linked_timeout(__io_prep_linked_timeout(req));
}

static inline void io_arm_ltimeout(struct io_kiocb *req)
{
        if (unlikely(req->flags & REQ_F_ARM_LTIMEOUT))
                __io_arm_ltimeout(req);
}

static void io_prep_async_work(struct io_kiocb *req)
{
        const struct io_issue_def *def = &io_issue_defs[req->opcode];
        struct io_ring_ctx *ctx = req->ctx;

        if (!(req->flags & REQ_F_CREDS)) {
                req->flags |= REQ_F_CREDS;
                req->creds = get_current_cred();
        }

        req->work.list.next = NULL;
        req->work.flags = 0;
        req->work.cancel_seq = atomic_read(&ctx->cancel_seq);
        if (req->flags & REQ_F_FORCE_ASYNC)
                req->work.flags |= IO_WQ_WORK_CONCURRENT;

        if (req->file && !io_req_ffs_set(req))
                req->flags |= io_file_get_flags(req->file) << REQ_F_SUPPORT_NOWAIT_BIT;

        if (req->flags & REQ_F_ISREG) {
                bool should_hash = def->hash_reg_file;

                /* don't serialize this request if the fs doesn't need it */
                if (should_hash && (req->file->f_flags & O_DIRECT) &&
                    (req->file->f_mode & FMODE_DIO_PARALLEL_WRITE))
                        should_hash = false;
                if (should_hash || (ctx->flags & IORING_SETUP_IOPOLL))
                        io_wq_hash_work(&req->work, file_inode(req->file));
        } else if (!req->file || !S_ISBLK(file_inode(req->file)->i_mode)) {
                if (def->unbound_nonreg_file)
                        req->work.flags |= IO_WQ_WORK_UNBOUND;
        }
}

static void io_prep_async_link(struct io_kiocb *req)
{
        struct io_kiocb *cur;

        if (req->flags & REQ_F_LINK_TIMEOUT) {
                struct io_ring_ctx *ctx = req->ctx;

                spin_lock_irq(&ctx->timeout_lock);
                io_for_each_link(cur, req)
                        io_prep_async_work(cur);
                spin_unlock_irq(&ctx->timeout_lock);
        } else {
                io_for_each_link(cur, req)
                        io_prep_async_work(cur);
        }
}

void io_queue_iowq(struct io_kiocb *req, struct io_tw_state *ts_dont_use)
{
        struct io_kiocb *link = io_prep_linked_timeout(req);
        struct io_uring_task *tctx = req->task->io_uring;

        BUG_ON(!tctx);
        BUG_ON(!tctx->io_wq);

        /* init ->work of the whole link before punting */
        io_prep_async_link(req);

        /*
         * Not expected to happen, but if we do have a bug where this _can_
         * happen, catch it here and ensure the request is marked as
         * canceled. That will make io-wq go through the usual work cancel
         * procedure rather than attempt to run this request (or create a new
         * worker for it).
         */
        if (WARN_ON_ONCE(!same_thread_group(req->task, current)))
                req->work.flags |= IO_WQ_WORK_CANCEL;

        trace_io_uring_queue_async_work(req, io_wq_is_hashed(&req->work));
        io_wq_enqueue(tctx->io_wq, &req->work);
        if (link)
                io_queue_linked_timeout(link);
}

static __cold void io_queue_deferred(struct io_ring_ctx *ctx)
{
        while (!list_empty(&ctx->defer_list)) {
                struct io_defer_entry *de = list_first_entry(&ctx->defer_list,
                                                struct io_defer_entry, list);

                if (req_need_defer(de->req, de->seq))
                        break;
                list_del_init(&de->list);
                io_req_task_queue(de->req);
                kfree(de);
        }
}


static void io_eventfd_ops(struct rcu_head *rcu)
{
        struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu);
        int ops = atomic_xchg(&ev_fd->ops, 0);

        if (ops & BIT(IO_EVENTFD_OP_SIGNAL_BIT))
                eventfd_signal_mask(ev_fd->cq_ev_fd, 1, EPOLL_URING_WAKE);

        /* IO_EVENTFD_OP_FREE_BIT may not be set here depending on callback
         * ordering in a race but if references are 0 we know we have to free
         * it regardless.
         */
        if (atomic_dec_and_test(&ev_fd->refs)) {
                eventfd_ctx_put(ev_fd->cq_ev_fd);
                kfree(ev_fd);
        }
}

static void io_eventfd_signal(struct io_ring_ctx *ctx)
{
        struct io_ev_fd *ev_fd = NULL;

        rcu_read_lock();
        /*
         * rcu_dereference ctx->io_ev_fd once and use it for both for checking
         * and eventfd_signal
         */
        ev_fd = rcu_dereference(ctx->io_ev_fd);

        /*
         * Check again if ev_fd exists incase an io_eventfd_unregister call
         * completed between the NULL check of ctx->io_ev_fd at the start of
         * the function and rcu_read_lock.
         */
        if (unlikely(!ev_fd))
                goto out;
        if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
                goto out;
        if (ev_fd->eventfd_async && !io_wq_current_is_worker())
                goto out;

        if (likely(eventfd_signal_allowed())) {
                eventfd_signal_mask(ev_fd->cq_ev_fd, 1, EPOLL_URING_WAKE);
        } else {
                atomic_inc(&ev_fd->refs);
                if (!atomic_fetch_or(BIT(IO_EVENTFD_OP_SIGNAL_BIT), &ev_fd->ops))
                        call_rcu_hurry(&ev_fd->rcu, io_eventfd_ops);
                else
                        atomic_dec(&ev_fd->refs);
        }

out:
        rcu_read_unlock();
}

static void io_eventfd_flush_signal(struct io_ring_ctx *ctx)
{
        bool skip;

        spin_lock(&ctx->completion_lock);

        /*
         * Eventfd should only get triggered when at least one event has been
         * posted. Some applications rely on the eventfd notification count
         * only changing IFF a new CQE has been added to the CQ ring. There's
         * no depedency on 1:1 relationship between how many times this
         * function is called (and hence the eventfd count) and number of CQEs
         * posted to the CQ ring.
         */
        skip = ctx->cached_cq_tail == ctx->evfd_last_cq_tail;
        ctx->evfd_last_cq_tail = ctx->cached_cq_tail;
        spin_unlock(&ctx->completion_lock);
        if (skip)
                return;

        io_eventfd_signal(ctx);
}

void __io_commit_cqring_flush(struct io_ring_ctx *ctx)
{
        if (ctx->poll_activated)
                io_poll_wq_wake(ctx);
        if (ctx->off_timeout_used)
                io_flush_timeouts(ctx);
        if (ctx->drain_active) {
                spin_lock(&ctx->completion_lock);
                io_queue_deferred(ctx);
                spin_unlock(&ctx->completion_lock);
        }
        if (ctx->has_evfd)
                io_eventfd_flush_signal(ctx);
}

static inline void __io_cq_lock(struct io_ring_ctx *ctx)
        __acquires(ctx->completion_lock)
{
        if (!ctx->task_complete)
                spin_lock(&ctx->completion_lock);
}

static inline void __io_cq_unlock(struct io_ring_ctx *ctx)
{
        if (!ctx->task_complete)
                spin_unlock(&ctx->completion_lock);
}

static inline void io_cq_lock(struct io_ring_ctx *ctx)
        __acquires(ctx->completion_lock)
{
        spin_lock(&ctx->completion_lock);
}

static inline void io_cq_unlock(struct io_ring_ctx *ctx)
        __releases(ctx->completion_lock)
{
        spin_unlock(&ctx->completion_lock);
}

/* keep it inlined for io_submit_flush_completions() */
static inline void __io_cq_unlock_post(struct io_ring_ctx *ctx)
        __releases(ctx->completion_lock)
{
        io_commit_cqring(ctx);
        __io_cq_unlock(ctx);
        io_commit_cqring_flush(ctx);
        io_cqring_wake(ctx);
}

static inline void __io_cq_unlock_post_flush(struct io_ring_ctx *ctx)
        __releases(ctx->completion_lock)
{
        io_commit_cqring(ctx);
        __io_cq_unlock(ctx);
        io_commit_cqring_flush(ctx);

        /*
         * As ->task_complete implies that the ring is single tasked, cq_wait
         * may only be waited on by the current in io_cqring_wait(), but since
         * it will re-check the wakeup conditions once we return we can safely
         * skip waking it up.
         */
        if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
                io_cqring_wake(ctx);
}

void io_cq_unlock_post(struct io_ring_ctx *ctx)
        __releases(ctx->completion_lock)
{
        io_commit_cqring(ctx);
        spin_unlock(&ctx->completion_lock);
        io_commit_cqring_flush(ctx);
        io_cqring_wake(ctx);
}

/* Returns true if there are no backlogged entries after the flush */
static void io_cqring_overflow_kill(struct io_ring_ctx *ctx)
{
        struct io_overflow_cqe *ocqe;
        LIST_HEAD(list);

        io_cq_lock(ctx);
        list_splice_init(&ctx->cq_overflow_list, &list);
        clear_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq);
        io_cq_unlock(ctx);

        while (!list_empty(&list)) {
                ocqe = list_first_entry(&list, struct io_overflow_cqe, list);
                list_del(&ocqe->list);
                kfree(ocqe);
        }
}

static void __io_cqring_overflow_flush(struct io_ring_ctx *ctx)
{
        size_t cqe_size = sizeof(struct io_uring_cqe);

        if (__io_cqring_events(ctx) == ctx->cq_entries)
                return;

        if (ctx->flags & IORING_SETUP_CQE32)
                cqe_size <<= 1;

        io_cq_lock(ctx);
        while (!list_empty(&ctx->cq_overflow_list)) {
                struct io_uring_cqe *cqe = io_get_cqe_overflow(ctx, true);
                struct io_overflow_cqe *ocqe;

                if (!cqe)
                        break;
                ocqe = list_first_entry(&ctx->cq_overflow_list,
                                        struct io_overflow_cqe, list);
                memcpy(cqe, &ocqe->cqe, cqe_size);
                list_del(&ocqe->list);
                kfree(ocqe);
        }

        if (list_empty(&ctx->cq_overflow_list)) {
                clear_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq);
                atomic_andnot(IORING_SQ_CQ_OVERFLOW, &ctx->rings->sq_flags);
        }
        io_cq_unlock_post(ctx);
}

static void io_cqring_do_overflow_flush(struct io_ring_ctx *ctx)
{
        /* iopoll syncs against uring_lock, not completion_lock */
        if (ctx->flags & IORING_SETUP_IOPOLL)
                mutex_lock(&ctx->uring_lock);
        __io_cqring_overflow_flush(ctx);
        if (ctx->flags & IORING_SETUP_IOPOLL)
                mutex_unlock(&ctx->uring_lock);
}

static void io_cqring_overflow_flush(struct io_ring_ctx *ctx)
{
        if (test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))
                io_cqring_do_overflow_flush(ctx);
}

/* can be called by any task */
static void io_put_task_remote(struct task_struct *task, int nr)
{
        struct io_uring_task *tctx = task->io_uring;

        percpu_counter_sub(&tctx->inflight, nr);
        if (unlikely(atomic_read(&tctx->in_cancel)))
                wake_up(&tctx->wait);
        put_task_struct_many(task, nr);
}

/* used by a task to put its own references */
static void io_put_task_local(struct task_struct *task, int nr)
{
        task->io_uring->cached_refs += nr;
}

/* must to be called somewhat shortly after putting a request */
static inline void io_put_task(struct task_struct *task, int nr)
{
        if (likely(task == current))
                io_put_task_local(task, nr);
        else
                io_put_task_remote(task, nr);
}

void io_task_refs_refill(struct io_uring_task *tctx)
{
        unsigned int refill = -tctx->cached_refs + IO_TCTX_REFS_CACHE_NR;

        percpu_counter_add(&tctx->inflight, refill);
        refcount_add(refill, &current->usage);
        tctx->cached_refs += refill;
}

static __cold void io_uring_drop_tctx_refs(struct task_struct *task)
{
        struct io_uring_task *tctx = task->io_uring;
        unsigned int refs = tctx->cached_refs;

        if (refs) {
                tctx->cached_refs = 0;
                percpu_counter_sub(&tctx->inflight, refs);
                put_task_struct_many(task, refs);
        }
}

static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data,
                                     s32 res, u32 cflags, u64 extra1, u64 extra2)
{
        struct io_overflow_cqe *ocqe;
        size_t ocq_size = sizeof(struct io_overflow_cqe);
        bool is_cqe32 = (ctx->flags & IORING_SETUP_CQE32);

        lockdep_assert_held(&ctx->completion_lock);

        if (is_cqe32)
                ocq_size += sizeof(struct io_uring_cqe);

        ocqe = kmalloc(ocq_size, GFP_ATOMIC | __GFP_ACCOUNT);
        trace_io_uring_cqe_overflow(ctx, user_data, res, cflags, ocqe);
        if (!ocqe) {
                /*
                 * If we're in ring overflow flush mode, or in task cancel mode,
                 * or cannot allocate an overflow entry, then we need to drop it
                 * on the floor.
                 */
                io_account_cq_overflow(ctx);
                set_bit(IO_CHECK_CQ_DROPPED_BIT, &ctx->check_cq);
                return false;
        }
        if (list_empty(&ctx->cq_overflow_list)) {
                set_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq);
                atomic_or(IORING_SQ_CQ_OVERFLOW, &ctx->rings->sq_flags);

        }
        ocqe->cqe.user_data = user_data;
        ocqe->cqe.res = res;
        ocqe->cqe.flags = cflags;
        if (is_cqe32) {
                ocqe->cqe.big_cqe[0] = extra1;
                ocqe->cqe.big_cqe[1] = extra2;
        }
        list_add_tail(&ocqe->list, &ctx->cq_overflow_list);
        return true;
}

bool io_req_cqe_overflow(struct io_kiocb *req)
{
        if (!(req->flags & REQ_F_CQE32_INIT)) {
                req->extra1 = 0;
                req->extra2 = 0;
        }
        return io_cqring_event_overflow(req->ctx, req->cqe.user_data,
                                        req->cqe.res, req->cqe.flags,
                                        req->extra1, req->extra2);
}

/*
 * writes to the cq entry need to come after reading head; the
 * control dependency is enough as we're using WRITE_ONCE to
 * fill the cq entry
 */
struct io_uring_cqe *__io_get_cqe(struct io_ring_ctx *ctx, bool overflow)
{
        struct io_rings *rings = ctx->rings;
        unsigned int off = ctx->cached_cq_tail & (ctx->cq_entries - 1);
        unsigned int free, queued, len;

        /*
         * Posting into the CQ when there are pending overflowed CQEs may break
         * ordering guarantees, which will affect links, F_MORE users and more.
         * Force overflow the completion.
         */
        if (!overflow && (ctx->check_cq & BIT(IO_CHECK_CQ_OVERFLOW_BIT)))
                return NULL;

        /* userspace may cheat modifying the tail, be safe and do min */
        queued = min(__io_cqring_events(ctx), ctx->cq_entries);
        free = ctx->cq_entries - queued;
        /* we need a contiguous range, limit based on the current array offset */
        len = min(free, ctx->cq_entries - off);
        if (!len)
                return NULL;

        if (ctx->flags & IORING_SETUP_CQE32) {
                off <<= 1;
                len <<= 1;
        }

        ctx->cqe_cached = &rings->cqes[off];
        ctx->cqe_sentinel = ctx->cqe_cached + len;

        ctx->cached_cq_tail++;
        ctx->cqe_cached++;
        if (ctx->flags & IORING_SETUP_CQE32)
                ctx->cqe_cached++;
        return &rings->cqes[off];
}

static bool io_fill_cqe_aux(struct io_ring_ctx *ctx, u64 user_data, s32 res,
                              u32 cflags)
{
        struct io_uring_cqe *cqe;

        ctx->cq_extra++;

        /*
         * If we can't get a cq entry, userspace overflowed the
         * submission (by quite a lot). Increment the overflow count in
         * the ring.
         */
        cqe = io_get_cqe(ctx);
        if (likely(cqe)) {
                trace_io_uring_complete(ctx, NULL, user_data, res, cflags, 0, 0);

                WRITE_ONCE(cqe->user_data, user_data);
                WRITE_ONCE(cqe->res, res);
                WRITE_ONCE(cqe->flags, cflags);

                if (ctx->flags & IORING_SETUP_CQE32) {
                        WRITE_ONCE(cqe->big_cqe[0], 0);
                        WRITE_ONCE(cqe->big_cqe[1], 0);
                }
                return true;
        }
        return false;
}

static void __io_flush_post_cqes(struct io_ring_ctx *ctx)
        __must_hold(&ctx->uring_lock)
{
        struct io_submit_state *state = &ctx->submit_state;
        unsigned int i;

        lockdep_assert_held(&ctx->uring_lock);
        for (i = 0; i < state->cqes_count; i++) {
                struct io_uring_cqe *cqe = &state->cqes[i];

                if (!io_fill_cqe_aux(ctx, cqe->user_data, cqe->res, cqe->flags)) {
                        if (ctx->task_complete) {
                                spin_lock(&ctx->completion_lock);
                                io_cqring_event_overflow(ctx, cqe->user_data,
                                                        cqe->res, cqe->flags, 0, 0);
                                spin_unlock(&ctx->completion_lock);
                        } else {
                                io_cqring_event_overflow(ctx, cqe->user_data,
                                                        cqe->res, cqe->flags, 0, 0);
                        }
                }
        }
        state->cqes_count = 0;
}

static bool __io_post_aux_cqe(struct io_ring_ctx *ctx, u64 user_data, s32 res, u32 cflags,
                              bool allow_overflow)
{
        bool filled;

        io_cq_lock(ctx);
        filled = io_fill_cqe_aux(ctx, user_data, res, cflags);
        if (!filled && allow_overflow)
                filled = io_cqring_event_overflow(ctx, user_data, res, cflags, 0, 0);

        io_cq_unlock_post(ctx);
        return filled;
}

bool io_post_aux_cqe(struct io_ring_ctx *ctx, u64 user_data, s32 res, u32 cflags)
{
        return __io_post_aux_cqe(ctx, user_data, res, cflags, true);
}

bool io_aux_cqe(struct io_ring_ctx *ctx, bool defer, u64 user_data, s32 res, u32 cflags,
                bool allow_overflow)
{
        struct io_uring_cqe *cqe;
        unsigned int length;

        if (!defer)
                return __io_post_aux_cqe(ctx, user_data, res, cflags, allow_overflow);

        length = ARRAY_SIZE(ctx->submit_state.cqes);

        lockdep_assert_held(&ctx->uring_lock);

        if (ctx->submit_state.cqes_count == length) {
                __io_cq_lock(ctx);
                __io_flush_post_cqes(ctx);
                /* no need to flush - flush is deferred */
                __io_cq_unlock_post(ctx);
        }

        /* For defered completions this is not as strict as it is otherwise,
         * however it's main job is to prevent unbounded posted completions,
         * and in that it works just as well.
         */
        if (!allow_overflow && test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))
                return false;

        cqe = &ctx->submit_state.cqes[ctx->submit_state.cqes_count++];
        cqe->user_data = user_data;
        cqe->res = res;
        cqe->flags = cflags;
        return true;
}

static void __io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_rsrc_node *rsrc_node = NULL;

        io_cq_lock(ctx);
        if (!(req->flags & REQ_F_CQE_SKIP))
                io_fill_cqe_req(ctx, req);

        /*
         * If we're the last reference to this request, add to our locked
         * free_list cache.
         */
        if (req_ref_put_and_test(req)) {
                if (req->flags & IO_REQ_LINK_FLAGS) {
                        if (req->flags & IO_DISARM_MASK)
                                io_disarm_next(req);
                        if (req->link) {
                                io_req_task_queue(req->link);
                                req->link = NULL;
                        }
                }
                io_put_kbuf_comp(req);
                io_dismantle_req(req);
                rsrc_node = req->rsrc_node;
                /*
                 * Selected buffer deallocation in io_clean_op() assumes that
                 * we don't hold ->completion_lock. Clean them here to avoid
                 * deadlocks.
                 */
                io_put_task_remote(req->task, 1);
                wq_list_add_head(&req->comp_list, &ctx->locked_free_list);
                ctx->locked_free_nr++;
        }
        io_cq_unlock_post(ctx);

        if (rsrc_node) {
                io_ring_submit_lock(ctx, issue_flags);
                io_put_rsrc_node(ctx, rsrc_node);
                io_ring_submit_unlock(ctx, issue_flags);
        }
}

void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
{
        if (req->ctx->task_complete && (issue_flags & IO_URING_F_IOWQ)) {
                req->io_task_work.func = io_req_task_complete;
                io_req_task_work_add(req);
        } else if (!(issue_flags & IO_URING_F_UNLOCKED) ||
                   !(req->ctx->flags & IORING_SETUP_IOPOLL)) {
                __io_req_complete_post(req, issue_flags);
        } else {
                struct io_ring_ctx *ctx = req->ctx;

                mutex_lock(&ctx->uring_lock);
                __io_req_complete_post(req, issue_flags & ~IO_URING_F_UNLOCKED);
                mutex_unlock(&ctx->uring_lock);
        }
}

void io_req_defer_failed(struct io_kiocb *req, s32 res)
        __must_hold(&ctx->uring_lock)
{
        const struct io_cold_def *def = &io_cold_defs[req->opcode];

        lockdep_assert_held(&req->ctx->uring_lock);

        req_set_fail(req);
        io_req_set_res(req, res, io_put_kbuf(req, IO_URING_F_UNLOCKED));
        if (def->fail)
                def->fail(req);
        io_req_complete_defer(req);
}

/*
 * Don't initialise the fields below on every allocation, but do that in
 * advance and keep them valid across allocations.
 */
static void io_preinit_req(struct io_kiocb *req, struct io_ring_ctx *ctx)
{
        req->ctx = ctx;
        req->link = NULL;
        req->async_data = NULL;
        /* not necessary, but safer to zero */
        req->cqe.res = 0;
}

static void io_flush_cached_locked_reqs(struct io_ring_ctx *ctx,
                                        struct io_submit_state *state)
{
        spin_lock(&ctx->completion_lock);
        wq_list_splice(&ctx->locked_free_list, &state->free_list);
        ctx->locked_free_nr = 0;
        spin_unlock(&ctx->completion_lock);
}

/*
 * A request might get retired back into the request caches even before opcode
 * handlers and io_issue_sqe() are done with it, e.g. inline completion path.
 * Because of that, io_alloc_req() should be called only under ->uring_lock
 * and with extra caution to not get a request that is still worked on.
 */
__cold bool __io_alloc_req_refill(struct io_ring_ctx *ctx)
        __must_hold(&ctx->uring_lock)
{
        gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
        void *reqs[IO_REQ_ALLOC_BATCH];
        int ret, i;

        /*
         * If we have more than a batch's worth of requests in our IRQ side
         * locked cache, grab the lock and move them over to our submission
         * side cache.
         */
        if (data_race(ctx->locked_free_nr) > IO_COMPL_BATCH) {
                io_flush_cached_locked_reqs(ctx, &ctx->submit_state);
                if (!io_req_cache_empty(ctx))
                        return true;
        }

        ret = kmem_cache_alloc_bulk(req_cachep, gfp, ARRAY_SIZE(reqs), reqs);

        /*
         * Bulk alloc is all-or-nothing. If we fail to get a batch,
         * retry single alloc to be on the safe side.
         */
        if (unlikely(ret <= 0)) {
                reqs[0] = kmem_cache_alloc(req_cachep, gfp);
                if (!reqs[0])
                        return false;
                ret = 1;
        }

        percpu_ref_get_many(&ctx->refs, ret);
        for (i = 0; i < ret; i++) {
                struct io_kiocb *req = reqs[i];

                io_preinit_req(req, ctx);
                io_req_add_to_cache(req, ctx);
        }
        return true;
}

static inline void io_dismantle_req(struct io_kiocb *req)
{
        unsigned int flags = req->flags;

        if (unlikely(flags & IO_REQ_CLEAN_FLAGS))
                io_clean_op(req);
        if (!(flags & REQ_F_FIXED_FILE))
                io_put_file(req->file);
}

static __cold void io_free_req_tw(struct io_kiocb *req, struct io_tw_state *ts)
{
        struct io_ring_ctx *ctx = req->ctx;

        if (req->rsrc_node) {
                io_tw_lock(ctx, ts);
                io_put_rsrc_node(ctx, req->rsrc_node);
        }
        io_dismantle_req(req);
        io_put_task_remote(req->task, 1);

        spin_lock(&ctx->completion_lock);
        wq_list_add_head(&req->comp_list, &ctx->locked_free_list);
        ctx->locked_free_nr++;
        spin_unlock(&ctx->completion_lock);
}

__cold void io_free_req(struct io_kiocb *req)
{
        req->io_task_work.func = io_free_req_tw;
        io_req_task_work_add(req);
}

static void __io_req_find_next_prep(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;

        spin_lock(&ctx->completion_lock);
        io_disarm_next(req);
        spin_unlock(&ctx->completion_lock);
}

static inline struct io_kiocb *io_req_find_next(struct io_kiocb *req)
{
        struct io_kiocb *nxt;

        /*
         * If LINK is set, we have dependent requests in this chain. If we
         * didn't fail this request, queue the first one up, moving any other
         * dependencies to the next request. In case of failure, fail the rest
         * of the chain.
         */
        if (unlikely(req->flags & IO_DISARM_MASK))
                __io_req_find_next_prep(req);
        nxt = req->link;
        req->link = NULL;
        return nxt;
}

static void ctx_flush_and_put(struct io_ring_ctx *ctx, struct io_tw_state *ts)
{
        if (!ctx)
                return;
        if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
                atomic_andnot(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
        if (ts->locked) {
                io_submit_flush_completions(ctx);
                mutex_unlock(&ctx->uring_lock);
                ts->locked = false;
        }
        percpu_ref_put(&ctx->refs);
}

static unsigned int handle_tw_list(struct llist_node *node,
                                   struct io_ring_ctx **ctx,
                                   struct io_tw_state *ts,
                                   struct llist_node *last)
{
        unsigned int count = 0;

        while (node && node != last) {
                struct llist_node *next = node->next;
                struct io_kiocb *req = container_of(node, struct io_kiocb,
                                                    io_task_work.node);

                prefetch(container_of(next, struct io_kiocb, io_task_work.node));

                if (req->ctx != *ctx) {
                        ctx_flush_and_put(*ctx, ts);
                        *ctx = req->ctx;
                        /* if not contended, grab and improve batching */
                        ts->locked = mutex_trylock(&(*ctx)->uring_lock);
                        percpu_ref_get(&(*ctx)->refs);
                }
                req->io_task_work.func(req, ts);
                node = next;
                count++;
                if (unlikely(need_resched())) {
                        ctx_flush_and_put(*ctx, ts);
                        *ctx = NULL;
                        cond_resched();
                }
        }

        return count;
}

/**
 * io_llist_xchg - swap all entries in a lock-less list
 * @head:       the head of lock-less list to delete all entries
 * @new:        new entry as the head of the list
 *
 * If list is empty, return NULL, otherwise, return the pointer to the first entry.
 * The order of entries returned is from the newest to the oldest added one.
 */
static inline struct llist_node *io_llist_xchg(struct llist_head *head,
                                               struct llist_node *new)
{
        return xchg(&head->first, new);
}

/**
 * io_llist_cmpxchg - possibly swap all entries in a lock-less list
 * @head:       the head of lock-less list to delete all entries
 * @old:        expected old value of the first entry of the list
 * @new:        new entry as the head of the list
 *
 * perform a cmpxchg on the first entry of the list.
 */

static inline struct llist_node *io_llist_cmpxchg(struct llist_head *head,
                                                  struct llist_node *old,
                                                  struct llist_node *new)
{
        return cmpxchg(&head->first, old, new);
}

void tctx_task_work(struct callback_head *cb)
{
        struct io_tw_state ts = {};
        struct io_ring_ctx *ctx = NULL;
        struct io_uring_task *tctx = container_of(cb, struct io_uring_task,
                                                  task_work);
        struct llist_node fake = {};
        struct llist_node *node;
        unsigned int loops = 0;
        unsigned int count = 0;

        if (unlikely(current->flags & PF_EXITING)) {
                io_fallback_tw(tctx);
                return;
        }

        do {
                loops++;
                node = io_llist_xchg(&tctx->task_list, &fake);
                count += handle_tw_list(node, &ctx, &ts, &fake);

                /* skip expensive cmpxchg if there are items in the list */
                if (READ_ONCE(tctx->task_list.first) != &fake)
                        continue;
                if (ts.locked && !wq_list_empty(&ctx->submit_state.compl_reqs)) {
                        io_submit_flush_completions(ctx);
                        if (READ_ONCE(tctx->task_list.first) != &fake)
                                continue;
                }
                node = io_llist_cmpxchg(&tctx->task_list, &fake, NULL);
        } while (node != &fake);

        ctx_flush_and_put(ctx, &ts);

        /* relaxed read is enough as only the task itself sets ->in_cancel */
        if (unlikely(atomic_read(&tctx->in_cancel)))
                io_uring_drop_tctx_refs(current);

        trace_io_uring_task_work_run(tctx, count, loops);
}

static __cold void io_fallback_tw(struct io_uring_task *tctx)
{
        struct llist_node *node = llist_del_all(&tctx->task_list);
        struct io_kiocb *req;

        while (node) {
                req = container_of(node, struct io_kiocb, io_task_work.node);
                node = node->next;
                if (llist_add(&req->io_task_work.node,
                              &req->ctx->fallback_llist))
                        schedule_delayed_work(&req->ctx->fallback_work, 1);
        }
}

static void io_req_local_work_add(struct io_kiocb *req, unsigned flags)
{
        struct io_ring_ctx *ctx = req->ctx;
        unsigned nr_wait, nr_tw, nr_tw_prev;
        struct llist_node *first;

        if (req->flags & (REQ_F_LINK | REQ_F_HARDLINK))
                flags &= ~IOU_F_TWQ_LAZY_WAKE;

        first = READ_ONCE(ctx->work_llist.first);
        do {
                nr_tw_prev = 0;
                if (first) {
                        struct io_kiocb *first_req = container_of(first,
                                                        struct io_kiocb,
                                                        io_task_work.node);
                        /*
                         * Might be executed at any moment, rely on
                         * SLAB_TYPESAFE_BY_RCU to keep it alive.
                         */
                        nr_tw_prev = READ_ONCE(first_req->nr_tw);
                }
                nr_tw = nr_tw_prev + 1;
                /* Large enough to fail the nr_wait comparison below */
                if (!(flags & IOU_F_TWQ_LAZY_WAKE))
                        nr_tw = -1U;

                req->nr_tw = nr_tw;
                req->io_task_work.node.next = first;
        } while (!try_cmpxchg(&ctx->work_llist.first, &first,
                              &req->io_task_work.node));

        if (!first) {
                if (unlikely(atomic_read(&req->task->io_uring->in_cancel))) {
                        io_move_task_work_from_local(ctx);
                        return;
                }
                if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
                        atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
                if (ctx->has_evfd)
                        io_eventfd_signal(ctx);
        }

        nr_wait = atomic_read(&ctx->cq_wait_nr);
        /* no one is waiting */
        if (!nr_wait)
                return;
        /* either not enough or the previous add has already woken it up */
        if (nr_wait > nr_tw || nr_tw_prev >= nr_wait)
                return;
        /* pairs with set_current_state() in io_cqring_wait() */
        smp_mb__after_atomic();
        wake_up_state(ctx->submitter_task, TASK_INTERRUPTIBLE);
}

void __io_req_task_work_add(struct io_kiocb *req, unsigned flags)
{
        struct io_uring_task *tctx = req->task->io_uring;
        struct io_ring_ctx *ctx = req->ctx;

        if (!(flags & IOU_F_TWQ_FORCE_NORMAL) &&
            (ctx->flags & IORING_SETUP_DEFER_TASKRUN)) {
                rcu_read_lock();
                io_req_local_work_add(req, flags);
                rcu_read_unlock();
                return;
        }

        /* task_work already pending, we're done */
        if (!llist_add(&req->io_task_work.node, &tctx->task_list))
                return;

        if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
                atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);

        if (likely(!task_work_add(req->task, &tctx->task_work, ctx->notify_method)))
                return;

        io_fallback_tw(tctx);
}

static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx)
{
        struct llist_node *node;

        node = llist_del_all(&ctx->work_llist);
        while (node) {
                struct io_kiocb *req = container_of(node, struct io_kiocb,
                                                    io_task_work.node);

                node = node->next;
                __io_req_task_work_add(req, IOU_F_TWQ_FORCE_NORMAL);
        }
}

static int __io_run_local_work(struct io_ring_ctx *ctx, struct io_tw_state *ts)
{
        struct llist_node *node;
        unsigned int loops = 0;
        int ret = 0;

        if (WARN_ON_ONCE(ctx->submitter_task != current))
                return -EEXIST;
        if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
                atomic_andnot(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
again:
        node = io_llist_xchg(&ctx->work_llist, NULL);
        while (node) {
                struct llist_node *next = node->next;
                struct io_kiocb *req = container_of(node, struct io_kiocb,
                                                    io_task_work.node);
                prefetch(container_of(next, struct io_kiocb, io_task_work.node));
                req->io_task_work.func(req, ts);
                ret++;
                node = next;
        }
        loops++;

        if (!llist_empty(&ctx->work_llist))
                goto again;
        if (ts->locked) {
                io_submit_flush_completions(ctx);
                if (!llist_empty(&ctx->work_llist))
                        goto again;
        }
        trace_io_uring_local_work_run(ctx, ret, loops);
        return ret;
}

static inline int io_run_local_work_locked(struct io_ring_ctx *ctx)
{
        struct io_tw_state ts = { .locked = true, };
        int ret;

        if (llist_empty(&ctx->work_llist))
                return 0;

        ret = __io_run_local_work(ctx, &ts);
        /* shouldn't happen! */
        if (WARN_ON_ONCE(!ts.locked))
                mutex_lock(&ctx->uring_lock);
        return ret;
}

static int io_run_local_work(struct io_ring_ctx *ctx)
{
        struct io_tw_state ts = {};
        int ret;

        ts.locked = mutex_trylock(&ctx->uring_lock);
        ret = __io_run_local_work(ctx, &ts);
        if (ts.locked)
                mutex_unlock(&ctx->uring_lock);

        return ret;
}

static void io_req_task_cancel(struct io_kiocb *req, struct io_tw_state *ts)
{
        io_tw_lock(req->ctx, ts);
        io_req_defer_failed(req, req->cqe.res);
}

void io_req_task_submit(struct io_kiocb *req, struct io_tw_state *ts)
{
        io_tw_lock(req->ctx, ts);
        /* req->task == current here, checking PF_EXITING is safe */
        if (unlikely(req->task->flags & PF_EXITING))
                io_req_defer_failed(req, -EFAULT);
        else if (req->flags & REQ_F_FORCE_ASYNC)
                io_queue_iowq(req, ts);
        else
                io_queue_sqe(req);
}

void io_req_task_queue_fail(struct io_kiocb *req, int ret)
{
        io_req_set_res(req, ret, 0);
        req->io_task_work.func = io_req_task_cancel;
        io_req_task_work_add(req);
}

void io_req_task_queue(struct io_kiocb *req)
{
        req->io_task_work.func = io_req_task_submit;
        io_req_task_work_add(req);
}

void io_queue_next(struct io_kiocb *req)
{
        struct io_kiocb *nxt = io_req_find_next(req);

        if (nxt)
                io_req_task_queue(nxt);
}

void io_free_batch_list(struct io_ring_ctx *ctx, struct io_wq_work_node *node)
        __must_hold(&ctx->uring_lock)
{
        struct task_struct *task = NULL;
        int task_refs = 0;

        do {
                struct io_kiocb *req = container_of(node, struct io_kiocb,
                                                    comp_list);

                if (unlikely(req->flags & IO_REQ_CLEAN_SLOW_FLAGS)) {
                        if (req->flags & REQ_F_REFCOUNT) {
                                node = req->comp_list.next;
                                if (!req_ref_put_and_test(req))
                                        continue;
                        }
                        if ((req->flags & REQ_F_POLLED) && req->apoll) {
                                struct async_poll *apoll = req->apoll;

                                if (apoll->double_poll)
                                        kfree(apoll->double_poll);
                                if (!io_alloc_cache_put(&ctx->apoll_cache, &apoll->cache))
                                        kfree(apoll);
                                req->flags &= ~REQ_F_POLLED;
                        }
                        if (req->flags & IO_REQ_LINK_FLAGS)
                                io_queue_next(req);
                        if (unlikely(req->flags & IO_REQ_CLEAN_FLAGS))
                                io_clean_op(req);
                }
                if (!(req->flags & REQ_F_FIXED_FILE))
                        io_put_file(req->file);

                io_req_put_rsrc_locked(req, ctx);

                if (req->task != task) {
                        if (task)
                                io_put_task(task, task_refs);
                        task = req->task;
                        task_refs = 0;
                }
                task_refs++;
                node = req->comp_list.next;
                io_req_add_to_cache(req, ctx);
        } while (node);

        if (task)
                io_put_task(task, task_refs);
}

static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
        __must_hold(&ctx->uring_lock)
{
        struct io_submit_state *state = &ctx->submit_state;
        struct io_wq_work_node *node;

        __io_cq_lock(ctx);
        /* must come first to preserve CQE ordering in failure cases */
        if (state->cqes_count)
                __io_flush_post_cqes(ctx);
        __wq_list_for_each(node, &state->compl_reqs) {
                struct io_kiocb *req = container_of(node, struct io_kiocb,
                                            comp_list);

                if (!(req->flags & REQ_F_CQE_SKIP) &&
                    unlikely(!__io_fill_cqe_req(ctx, req))) {
                        if (ctx->task_complete) {
                                spin_lock(&ctx->completion_lock);
                                io_req_cqe_overflow(req);
                                spin_unlock(&ctx->completion_lock);
                        } else {
                                io_req_cqe_overflow(req);
                        }
                }
        }
        __io_cq_unlock_post_flush(ctx);

        if (!wq_list_empty(&ctx->submit_state.compl_reqs)) {
                io_free_batch_list(ctx, state->compl_reqs.first);
                INIT_WQ_LIST(&state->compl_reqs);
        }
}

/*
 * Drop reference to request, return next in chain (if there is one) if this
 * was the last reference to this request.
 */
static inline struct io_kiocb *io_put_req_find_next(struct io_kiocb *req)
{
        struct io_kiocb *nxt = NULL;

        if (req_ref_put_and_test(req)) {
                if (unlikely(req->flags & IO_REQ_LINK_FLAGS))
                        nxt = io_req_find_next(req);
                io_free_req(req);
        }
        return nxt;
}

static unsigned io_cqring_events(struct io_ring_ctx *ctx)
{
        /* See comment at the top of this file */
        smp_rmb();
        return __io_cqring_events(ctx);
}

/*
 * We can't just wait for polled events to come to us, we have to actively
 * find and complete them.
 */
static __cold void io_iopoll_try_reap_events(struct io_ring_ctx *ctx)
{
        if (!(ctx->flags & IORING_SETUP_IOPOLL))
                return;

        mutex_lock(&ctx->uring_lock);
        while (!wq_list_empty(&ctx->iopoll_list)) {
                /* let it sleep and repeat later if can't complete a request */
                if (io_do_iopoll(ctx, true) == 0)
                        break;
                /*
                 * Ensure we allow local-to-the-cpu processing to take place,
                 * in this case we need to ensure that we reap all events.
                 * Also let task_work, etc. to progress by releasing the mutex
                 */
                if (need_resched()) {
                        mutex_unlock(&ctx->uring_lock);
                        cond_resched();
                        mutex_lock(&ctx->uring_lock);
                }
        }
        mutex_unlock(&ctx->uring_lock);
}

static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
{
        unsigned int nr_events = 0;
        int ret = 0;
        unsigned long check_cq;

        if (!io_allowed_run_tw(ctx))
                return -EEXIST;

        check_cq = READ_ONCE(ctx->check_cq);
        if (unlikely(check_cq)) {
                if (check_cq & BIT(IO_CHECK_CQ_OVERFLOW_BIT))
                        __io_cqring_overflow_flush(ctx);
                /*
                 * Similarly do not spin if we have not informed the user of any
                 * dropped CQE.
                 */
                if (check_cq & BIT(IO_CHECK_CQ_DROPPED_BIT))
                        return -EBADR;
        }
        /*
         * Don't enter poll loop if we already have events pending.
         * If we do, we can potentially be spinning for commands that
         * already triggered a CQE (eg in error).
         */
        if (io_cqring_events(ctx))
                return 0;

        do {
                /*
                 * If a submit got punted to a workqueue, we can have the
                 * application entering polling for a command before it gets
                 * issued. That app will hold the uring_lock for the duration
                 * of the poll right here, so we need to take a breather every
                 * now and then to ensure that the issue has a chance to add
                 * the poll to the issued list. Otherwise we can spin here
                 * forever, while the workqueue is stuck trying to acquire the
                 * very same mutex.
                 */
                if (wq_list_empty(&ctx->iopoll_list) ||
                    io_task_work_pending(ctx)) {
                        u32 tail = ctx->cached_cq_tail;

                        (void) io_run_local_work_locked(ctx);

                        if (task_work_pending(current) ||
                            wq_list_empty(&ctx->iopoll_list)) {
                                mutex_unlock(&ctx->uring_lock);
                                io_run_task_work();
                                mutex_lock(&ctx->uring_lock);
                        }
                        /* some requests don't go through iopoll_list */
                        if (tail != ctx->cached_cq_tail ||
                            wq_list_empty(&ctx->iopoll_list))
                                break;
                }
                ret = io_do_iopoll(ctx, !min);
                if (ret < 0)
                        break;
                nr_events += ret;
                ret = 0;
        } while (nr_events < min && !need_resched());

        return ret;
}

void io_req_task_complete(struct io_kiocb *req, struct io_tw_state *ts)
{
        if (ts->locked)
                io_req_complete_defer(req);
        else
                io_req_complete_post(req, IO_URING_F_UNLOCKED);
}

/*
 * After the iocb has been issued, it's safe to be found on the poll list.
 * Adding the kiocb to the list AFTER submission ensures that we don't
 * find it from a io_do_iopoll() thread before the issuer is done
 * accessing the kiocb cookie.
 */
static void io_iopoll_req_issued(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_ring_ctx *ctx = req->ctx;
        const bool needs_lock = issue_flags & IO_URING_F_UNLOCKED;

        /* workqueue context doesn't hold uring_lock, grab it now */
        if (unlikely(needs_lock))
                mutex_lock(&ctx->uring_lock);

        /*
         * Track whether we have multiple files in our lists. This will impact
         * how we do polling eventually, not spinning if we're on potentially
         * different devices.
         */
        if (wq_list_empty(&ctx->iopoll_list)) {
                ctx->poll_multi_queue = false;
        } else if (!ctx->poll_multi_queue) {
                struct io_kiocb *list_req;

                list_req = container_of(ctx->iopoll_list.first, struct io_kiocb,
                                        comp_list);
                if (list_req->file != req->file)
                        ctx->poll_multi_queue = true;
        }

        /*
         * For fast devices, IO may have already completed. If it has, add
         * it to the front so we find it first.
         */
        if (READ_ONCE(req->iopoll_completed))
                wq_list_add_head(&req->comp_list, &ctx->iopoll_list);
        else
                wq_list_add_tail(&req->comp_list, &ctx->iopoll_list);

        if (unlikely(needs_lock)) {
                /*
                 * If IORING_SETUP_SQPOLL is enabled, sqes are either handle
                 * in sq thread task context or in io worker task context. If
                 * current task context is sq thread, we don't need to check
                 * whether should wake up sq thread.
                 */
                if ((ctx->flags & IORING_SETUP_SQPOLL) &&
                    wq_has_sleeper(&ctx->sq_data->wait))
                        wake_up(&ctx->sq_data->wait);

                mutex_unlock(&ctx->uring_lock);
        }
}

static bool io_bdev_nowait(struct block_device *bdev)
{
        return !bdev || bdev_nowait(bdev);
}

/*
 * If we tracked the file through the SCM inflight mechanism, we could support
 * any file. For now, just ensure that anything potentially problematic is done
 * inline.
 */
static bool __io_file_supports_nowait(struct file *file, umode_t mode)
{
        if (S_ISBLK(mode)) {
                if (IS_ENABLED(CONFIG_BLOCK) &&
                    io_bdev_nowait(I_BDEV(file->f_mapping->host)))
                        return true;
                return false;
        }
        if (S_ISSOCK(mode))
                return true;
        if (S_ISREG(mode)) {
                if (IS_ENABLED(CONFIG_BLOCK) &&
                    io_bdev_nowait(file->f_inode->i_sb->s_bdev) &&
                    !io_is_uring_fops(file))
                        return true;
                return false;
        }

        /* any ->read/write should understand O_NONBLOCK */
        if (file->f_flags & O_NONBLOCK)
                return true;
        return file->f_mode & FMODE_NOWAIT;
}

/*
 * If we tracked the file through the SCM inflight mechanism, we could support
 * any file. For now, just ensure that anything potentially problematic is done
 * inline.
 */
unsigned int io_file_get_flags(struct file *file)
{
        umode_t mode = file_inode(file)->i_mode;
        unsigned int res = 0;

        if (S_ISREG(mode))
                res |= FFS_ISREG;
        if (__io_file_supports_nowait(file, mode))
                res |= FFS_NOWAIT;
        return res;
}

bool io_alloc_async_data(struct io_kiocb *req)
{
        WARN_ON_ONCE(!io_cold_defs[req->opcode].async_size);
        req->async_data = kmalloc(io_cold_defs[req->opcode].async_size, GFP_KERNEL);
        if (req->async_data) {
                req->flags |= REQ_F_ASYNC_DATA;
                return false;
        }
        return true;
}

int io_req_prep_async(struct io_kiocb *req)
{
        const struct io_cold_def *cdef = &io_cold_defs[req->opcode];
        const struct io_issue_def *def = &io_issue_defs[req->opcode];

        /* assign early for deferred execution for non-fixed file */
        if (def->needs_file && !(req->flags & REQ_F_FIXED_FILE) && !req->file)
                req->file = io_file_get_normal(req, req->cqe.fd);
        if (!cdef->prep_async)
                return 0;
        if (WARN_ON_ONCE(req_has_async_data(req)))
                return -EFAULT;
        if (!def->manual_alloc) {
                if (io_alloc_async_data(req))
                        return -EAGAIN;
        }
        return cdef->prep_async(req);
}

static u32 io_get_sequence(struct io_kiocb *req)
{
        u32 seq = req->ctx->cached_sq_head;
        struct io_kiocb *cur;

        /* need original cached_sq_head, but it was increased for each req */
        io_for_each_link(cur, req)
                seq--;
        return seq;
}

static __cold void io_drain_req(struct io_kiocb *req)
        __must_hold(&ctx->uring_lock)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_defer_entry *de;
        int ret;
        u32 seq = io_get_sequence(req);

        /* Still need defer if there is pending req in defer list. */
        spin_lock(&ctx->completion_lock);
        if (!req_need_defer(req, seq) && list_empty_careful(&ctx->defer_list)) {
                spin_unlock(&ctx->completion_lock);
queue:
                ctx->drain_active = false;
                io_req_task_queue(req);
                return;
        }
        spin_unlock(&ctx->completion_lock);

        io_prep_async_link(req);
        de = kmalloc(sizeof(*de), GFP_KERNEL);
        if (!de) {
                ret = -ENOMEM;
                io_req_defer_failed(req, ret);
                return;
        }

        spin_lock(&ctx->completion_lock);
        if (!req_need_defer(req, seq) && list_empty(&ctx->defer_list)) {
                spin_unlock(&ctx->completion_lock);
                kfree(de);
                goto queue;
        }

        trace_io_uring_defer(req);
        de->req = req;
        de->seq = seq;
        list_add_tail(&de->list, &ctx->defer_list);
        spin_unlock(&ctx->completion_lock);
}

static void io_clean_op(struct io_kiocb *req)
{
        if (req->flags & REQ_F_BUFFER_SELECTED) {
                spin_lock(&req->ctx->completion_lock);
                io_put_kbuf_comp(req);
                spin_unlock(&req->ctx->completion_lock);
        }

        if (req->flags & REQ_F_NEED_CLEANUP) {
                const struct io_cold_def *def = &io_cold_defs[req->opcode];

                if (def->cleanup)
                        def->cleanup(req);
        }
        if ((req->flags & REQ_F_POLLED) && req->apoll) {
                kfree(req->apoll->double_poll);
                kfree(req->apoll);
                req->apoll = NULL;
        }
        if (req->flags & REQ_F_INFLIGHT) {
                struct io_uring_task *tctx = req->task->io_uring;

                atomic_dec(&tctx->inflight_tracked);
        }
        if (req->flags & REQ_F_CREDS)
                put_cred(req->creds);
        if (req->flags & REQ_F_ASYNC_DATA) {
                kfree(req->async_data);
                req->async_data = NULL;
        }
        req->flags &= ~IO_REQ_CLEAN_FLAGS;
}

static bool io_assign_file(struct io_kiocb *req, const struct io_issue_def *def,
                           unsigned int issue_flags)
{
        if (req->file || !def->needs_file)
                return true;

        if (req->flags & REQ_F_FIXED_FILE)
                req->file = io_file_get_fixed(req, req->cqe.fd, issue_flags);
        else
                req->file = io_file_get_normal(req, req->cqe.fd);

        return !!req->file;
}

static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
{
        const struct io_issue_def *def = &io_issue_defs[req->opcode];
        const struct cred *creds = NULL;
        int ret;

        if (unlikely(!io_assign_file(req, def, issue_flags)))
                return -EBADF;

        if (unlikely((req->flags & REQ_F_CREDS) && req->creds != current_cred()))
                creds = override_creds(req->creds);

        if (!def->audit_skip)
                audit_uring_entry(req->opcode);

        ret = def->issue(req, issue_flags);

        if (!def->audit_skip)
                audit_uring_exit(!ret, ret);

        if (creds)
                revert_creds(creds);

        if (ret == IOU_OK) {
                if (issue_flags & IO_URING_F_COMPLETE_DEFER)
                        io_req_complete_defer(req);
                else
                        io_req_complete_post(req, issue_flags);
        } else if (ret != IOU_ISSUE_SKIP_COMPLETE)
                return ret;

        /* If the op doesn't have a file, we're not polling for it */
        if ((req->ctx->flags & IORING_SETUP_IOPOLL) && def->iopoll_queue)
                io_iopoll_req_issued(req, issue_flags);

        return 0;
}

int io_poll_issue(struct io_kiocb *req, struct io_tw_state *ts)
{
        io_tw_lock(req->ctx, ts);
        return io_issue_sqe(req, IO_URING_F_NONBLOCK|IO_URING_F_MULTISHOT|
                                 IO_URING_F_COMPLETE_DEFER);
}

struct io_wq_work *io_wq_free_work(struct io_wq_work *work)
{
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);

        req = io_put_req_find_next(req);
        return req ? &req->work : NULL;
}

void io_wq_submit_work(struct io_wq_work *work)
{
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);
        const struct io_issue_def *def = &io_issue_defs[req->opcode];
        unsigned int issue_flags = IO_URING_F_UNLOCKED | IO_URING_F_IOWQ;
        bool needs_poll = false;
        int ret = 0, err = -ECANCELED;

        /* one will be dropped by ->io_wq_free_work() after returning to io-wq */
        if (!(req->flags & REQ_F_REFCOUNT))
                __io_req_set_refcount(req, 2);
        else
                req_ref_get(req);

        io_arm_ltimeout(req);

        /* either cancelled or io-wq is dying, so don't touch tctx->iowq */
        if (work->flags & IO_WQ_WORK_CANCEL) {
fail:
                io_req_task_queue_fail(req, err);
                return;
        }
        if (!io_assign_file(req, def, issue_flags)) {
                err = -EBADF;
                work->flags |= IO_WQ_WORK_CANCEL;
                goto fail;
        }

        if (req->flags & REQ_F_FORCE_ASYNC) {
                bool opcode_poll = def->pollin || def->pollout;

                if (opcode_poll && file_can_poll(req->file)) {
                        needs_poll = true;
                        issue_flags |= IO_URING_F_NONBLOCK;
                }
        }

        do {
                ret = io_issue_sqe(req, issue_flags);
                if (ret != -EAGAIN)
                        break;
                /*
                 * We can get EAGAIN for iopolled IO even though we're
                 * forcing a sync submission from here, since we can't
                 * wait for request slots on the block side.
                 */
                if (!needs_poll) {
                        if (!(req->ctx->flags & IORING_SETUP_IOPOLL))
                                break;
                        cond_resched();
                        continue;
                }

                if (io_arm_poll_handler(req, issue_flags) == IO_APOLL_OK)
                        return;
                /* aborted or ready, in either case retry blocking */
                needs_poll = false;
                issue_flags &= ~IO_URING_F_NONBLOCK;
        } while (1);

        /* avoid locking problems by failing it from a clean context */
        if (ret < 0)
                io_req_task_queue_fail(req, ret);
}

inline struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
                                      unsigned int issue_flags)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct file *file = NULL;
        unsigned long file_ptr;

        io_ring_submit_lock(ctx, issue_flags);

        if (unlikely((unsigned int)fd >= ctx->nr_user_files))
                goto out;
        fd = array_index_nospec(fd, ctx->nr_user_files);
        file_ptr = io_fixed_file_slot(&ctx->file_table, fd)->file_ptr;
        file = (struct file *) (file_ptr & FFS_MASK);
        file_ptr &= ~FFS_MASK;
        /* mask in overlapping REQ_F and FFS bits */
        req->flags |= (file_ptr << REQ_F_SUPPORT_NOWAIT_BIT);
        io_req_set_rsrc_node(req, ctx, 0);
out:
        io_ring_submit_unlock(ctx, issue_flags);
        return file;
}

struct file *io_file_get_normal(struct io_kiocb *req, int fd)
{
        struct file *file = fget(fd);

        trace_io_uring_file_get(req, fd);

        /* we don't allow fixed io_uring files */
        if (file && io_is_uring_fops(file))
                io_req_track_inflight(req);
        return file;
}

static void io_queue_async(struct io_kiocb *req, int ret)
        __must_hold(&req->ctx->uring_lock)
{
        struct io_kiocb *linked_timeout;

        if (ret != -EAGAIN || (req->flags & REQ_F_NOWAIT)) {
                io_req_defer_failed(req, ret);
                return;
        }

        linked_timeout = io_prep_linked_timeout(req);

        switch (io_arm_poll_handler(req, 0)) {
        case IO_APOLL_READY:
                io_kbuf_recycle(req, 0);
                io_req_task_queue(req);
                break;
        case IO_APOLL_ABORTED:
                io_kbuf_recycle(req, 0);
                io_queue_iowq(req, NULL);
                break;
        case IO_APOLL_OK:
                break;
        }

        if (linked_timeout)
                io_queue_linked_timeout(linked_timeout);
}

static inline void io_queue_sqe(struct io_kiocb *req)
        __must_hold(&req->ctx->uring_lock)
{
        int ret;

        ret = io_issue_sqe(req, IO_URING_F_NONBLOCK|IO_URING_F_COMPLETE_DEFER);

        /*
         * We async punt it if the file wasn't marked NOWAIT, or if the file
         * doesn't support non-blocking read/write attempts
         */
        if (likely(!ret))
                io_arm_ltimeout(req);
        else
                io_queue_async(req, ret);
}

static void io_queue_sqe_fallback(struct io_kiocb *req)
        __must_hold(&req->ctx->uring_lock)
{
        if (unlikely(req->flags & REQ_F_FAIL)) {
                /*
                 * We don't submit, fail them all, for that replace hardlinks
                 * with normal links. Extra REQ_F_LINK is tolerated.
                 */
                req->flags &= ~REQ_F_HARDLINK;
                req->flags |= REQ_F_LINK;
                io_req_defer_failed(req, req->cqe.res);
        } else {
                int ret = io_req_prep_async(req);

                if (unlikely(ret)) {
                        io_req_defer_failed(req, ret);
                        return;
                }

                if (unlikely(req->ctx->drain_active))
                        io_drain_req(req);
                else
                        io_queue_iowq(req, NULL);
        }
}

/*
 * Check SQE restrictions (opcode and flags).
 *
 * Returns 'true' if SQE is allowed, 'false' otherwise.
 */
static inline bool io_check_restriction(struct io_ring_ctx *ctx,
                                        struct io_kiocb *req,
                                        unsigned int sqe_flags)
{
        if (!test_bit(req->opcode, ctx->restrictions.sqe_op))
                return false;

        if ((sqe_flags & ctx->restrictions.sqe_flags_required) !=
            ctx->restrictions.sqe_flags_required)
                return false;

        if (sqe_flags & ~(ctx->restrictions.sqe_flags_allowed |
                          ctx->restrictions.sqe_flags_required))
                return false;

        return true;
}

static void io_init_req_drain(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_kiocb *head = ctx->submit_state.link.head;

        ctx->drain_active = true;
        if (head) {
                /*
                 * If we need to drain a request in the middle of a link, drain
                 * the head request and the next request/link after the current
                 * link. Considering sequential execution of links,
                 * REQ_F_IO_DRAIN will be maintained for every request of our
                 * link.
                 */
                head->flags |= REQ_F_IO_DRAIN | REQ_F_FORCE_ASYNC;
                ctx->drain_next = true;
        }
}

static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
                       const struct io_uring_sqe *sqe)
        __must_hold(&ctx->uring_lock)
{
        const struct io_issue_def *def;
        unsigned int sqe_flags;
        int personality;
        u8 opcode;

        /* req is partially pre-initialised, see io_preinit_req() */
        req->opcode = opcode = READ_ONCE(sqe->opcode);
        /* same numerical values with corresponding REQ_F_*, safe to copy */
        req->flags = sqe_flags = READ_ONCE(sqe->flags);
        req->cqe.user_data = READ_ONCE(sqe->user_data);
        req->file = NULL;
        req->rsrc_node = NULL;
        req->task = current;

        if (unlikely(opcode >= IORING_OP_LAST)) {
                req->opcode = 0;
                return -EINVAL;
        }
        def = &io_issue_defs[opcode];
        if (unlikely(sqe_flags & ~SQE_COMMON_FLAGS)) {
                /* enforce forwards compatibility on users */
                if (sqe_flags & ~SQE_VALID_FLAGS)
                        return -EINVAL;
                if (sqe_flags & IOSQE_BUFFER_SELECT) {
                        if (!def->buffer_select)
                                return -EOPNOTSUPP;
                        req->buf_index = READ_ONCE(sqe->buf_group);
                }
                if (sqe_flags & IOSQE_CQE_SKIP_SUCCESS)
                        ctx->drain_disabled = true;
                if (sqe_flags & IOSQE_IO_DRAIN) {
                        if (ctx->drain_disabled)
                                return -EOPNOTSUPP;
                        io_init_req_drain(req);
                }
        }
        if (unlikely(ctx->restricted || ctx->drain_active || ctx->drain_next)) {
                if (ctx->restricted && !io_check_restriction(ctx, req, sqe_flags))
                        return -EACCES;
                /* knock it to the slow queue path, will be drained there */
                if (ctx->drain_active)
                        req->flags |= REQ_F_FORCE_ASYNC;
                /* if there is no link, we're at "next" request and need to drain */
                if (unlikely(ctx->drain_next) && !ctx->submit_state.link.head) {
                        ctx->drain_next = false;
                        ctx->drain_active = true;
                        req->flags |= REQ_F_IO_DRAIN | REQ_F_FORCE_ASYNC;
                }
        }

        if (!def->ioprio && sqe->ioprio)
                return -EINVAL;
        if (!def->iopoll && (ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;

        if (def->needs_file) {
                struct io_submit_state *state = &ctx->submit_state;

                req->cqe.fd = READ_ONCE(sqe->fd);

                /*
                 * Plug now if we have more than 2 IO left after this, and the
                 * target is potentially a read/write to block based storage.
                 */
                if (state->need_plug && def->plug) {
                        state->plug_started = true;
                        state->need_plug = false;
                        blk_start_plug_nr_ios(&state->plug, state->submit_nr);
                }
        }

        personality = READ_ONCE(sqe->personality);
        if (personality) {
                int ret;

                req->creds = xa_load(&ctx->personalities, personality);
                if (!req->creds)
                        return -EINVAL;
                get_cred(req->creds);
                ret = security_uring_override_creds(req->creds);
                if (ret) {
                        put_cred(req->creds);
                        return ret;
                }
                req->flags |= REQ_F_CREDS;
        }

        return def->prep(req, sqe);
}

static __cold int io_submit_fail_init(const struct io_uring_sqe *sqe,
                                      struct io_kiocb *req, int ret)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_submit_link *link = &ctx->submit_state.link;
        struct io_kiocb *head = link->head;

        trace_io_uring_req_failed(sqe, req, ret);

        /*
         * Avoid breaking links in the middle as it renders links with SQPOLL
         * unusable. Instead of failing eagerly, continue assembling the link if
         * applicable and mark the head with REQ_F_FAIL. The link flushing code
         * should find the flag and handle the rest.
         */
        req_fail_link_node(req, ret);
        if (head && !(head->flags & REQ_F_FAIL))
                req_fail_link_node(head, -ECANCELED);

        if (!(req->flags & IO_REQ_LINK_FLAGS)) {
                if (head) {
                        link->last->link = req;
                        link->head = NULL;
                        req = head;
                }
                io_queue_sqe_fallback(req);
                return ret;
        }

        if (head)
                link->last->link = req;
        else
                link->head = req;
        link->last = req;
        return 0;
}

static inline int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
                         const struct io_uring_sqe *sqe)
        __must_hold(&ctx->uring_lock)
{
        struct io_submit_link *link = &ctx->submit_state.link;
        int ret;

        ret = io_init_req(ctx, req, sqe);
        if (unlikely(ret))
                return io_submit_fail_init(sqe, req, ret);

        trace_io_uring_submit_req(req);

        /*
         * If we already have a head request, queue this one for async
         * submittal once the head completes. If we don't have a head but
         * IOSQE_IO_LINK is set in the sqe, start a new head. This one will be
         * submitted sync once the chain is complete. If none of those
         * conditions are true (normal request), then just queue it.
         */
        if (unlikely(link->head)) {
                ret = io_req_prep_async(req);
                if (unlikely(ret))
                        return io_submit_fail_init(sqe, req, ret);

                trace_io_uring_link(req, link->head);
                link->last->link = req;
                link->last = req;

                if (req->flags & IO_REQ_LINK_FLAGS)
                        return 0;
                /* last request of the link, flush it */
                req = link->head;
                link->head = NULL;
                if (req->flags & (REQ_F_FORCE_ASYNC | REQ_F_FAIL))
                        goto fallback;

        } else if (unlikely(req->flags & (IO_REQ_LINK_FLAGS |
                                          REQ_F_FORCE_ASYNC | REQ_F_FAIL))) {
                if (req->flags & IO_REQ_LINK_FLAGS) {
                        link->head = req;
                        link->last = req;
                } else {
fallback:
                        io_queue_sqe_fallback(req);
                }
                return 0;
        }

        io_queue_sqe(req);
        return 0;
}

/*
 * Batched submission is done, ensure local IO is flushed out.
 */
static void io_submit_state_end(struct io_ring_ctx *ctx)
{
        struct io_submit_state *state = &ctx->submit_state;

        if (unlikely(state->link.head))
                io_queue_sqe_fallback(state->link.head);
        /* flush only after queuing links as they can generate completions */
        io_submit_flush_completions(ctx);
        if (state->plug_started)
                blk_finish_plug(&state->plug);
}

/*
 * Start submission side cache.
 */
static void io_submit_state_start(struct io_submit_state *state,
                                  unsigned int max_ios)
{
        state->plug_started = false;
        state->need_plug = max_ios > 2;
        state->submit_nr = max_ios;
        /* set only head, no need to init link_last in advance */
        state->link.head = NULL;
}

static void io_commit_sqring(struct io_ring_ctx *ctx)
{
        struct io_rings *rings = ctx->rings;

        /*
         * Ensure any loads from the SQEs are done at this point,
         * since once we write the new head, the application could
         * write new data to them.
         */
        smp_store_release(&rings->sq.head, ctx->cached_sq_head);
}

/*
 * Fetch an sqe, if one is available. Note this returns a pointer to memory
 * that is mapped by userspace. This means that care needs to be taken to
 * ensure that reads are stable, as we cannot rely on userspace always
 * being a good citizen. If members of the sqe are validated and then later
 * used, it's important that those reads are done through READ_ONCE() to
 * prevent a re-load down the line.
 */
static bool io_get_sqe(struct io_ring_ctx *ctx, const struct io_uring_sqe **sqe)
{
        unsigned head, mask = ctx->sq_entries - 1;
        unsigned sq_idx = ctx->cached_sq_head++ & mask;

        /*
         * The cached sq head (or cq tail) serves two purposes:
         *
         * 1) allows us to batch the cost of updating the user visible
         *    head updates.
         * 2) allows the kernel side to track the head on its own, even
         *    though the application is the one updating it.
         */
        head = READ_ONCE(ctx->sq_array[sq_idx]);
        if (likely(head < ctx->sq_entries)) {
                /* double index for 128-byte SQEs, twice as long */
                if (ctx->flags & IORING_SETUP_SQE128)
                        head <<= 1;
                *sqe = &ctx->sq_sqes[head];
                return true;
        }

        /* drop invalid entries */
        ctx->cq_extra--;
        WRITE_ONCE(ctx->rings->sq_dropped,
                   READ_ONCE(ctx->rings->sq_dropped) + 1);
        return false;
}

int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
        __must_hold(&ctx->uring_lock)
{
        unsigned int entries = io_sqring_entries(ctx);
        unsigned int left;
        int ret;

        if (unlikely(!entries))
                return 0;
        /* make sure SQ entry isn't read before tail */
        ret = left = min(nr, entries);
        io_get_task_refs(left);
        io_submit_state_start(&ctx->submit_state, left);

        do {
                const struct io_uring_sqe *sqe;
                struct io_kiocb *req;

                if (unlikely(!io_alloc_req(ctx, &req)))
                        break;
                if (unlikely(!io_get_sqe(ctx, &sqe))) {
                        io_req_add_to_cache(req, ctx);
                        break;
                }

                /*
                 * Continue submitting even for sqe failure if the
                 * ring was setup with IORING_SETUP_SUBMIT_ALL
                 */
                if (unlikely(io_submit_sqe(ctx, req, sqe)) &&
                    !(ctx->flags & IORING_SETUP_SUBMIT_ALL)) {
                        left--;
                        break;
                }
        } while (--left);

        if (unlikely(left)) {
                ret -= left;
                /* try again if it submitted nothing and can't allocate a req */
                if (!ret && io_req_cache_empty(ctx))
                        ret = -EAGAIN;
                current->io_uring->cached_refs += left;
        }

        io_submit_state_end(ctx);
         /* Commit SQ ring head once we've consumed and submitted all SQEs */
        io_commit_sqring(ctx);
        return ret;
}

struct io_wait_queue {
        struct wait_queue_entry wq;
        struct io_ring_ctx *ctx;
        unsigned cq_tail;
        unsigned nr_timeouts;
        ktime_t timeout;
};

static inline bool io_has_work(struct io_ring_ctx *ctx)
{
        return test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq) ||
               !llist_empty(&ctx->work_llist);
}

static inline bool io_should_wake(struct io_wait_queue *iowq)
{
        struct io_ring_ctx *ctx = iowq->ctx;
        int dist = READ_ONCE(ctx->rings->cq.tail) - (int) iowq->cq_tail;

        /*
         * Wake up if we have enough events, or if a timeout occurred since we
         * started waiting. For timeouts, we always want to return to userspace,
         * regardless of event count.
         */
        return dist >= 0 || atomic_read(&ctx->cq_timeouts) != iowq->nr_timeouts;
}

static int io_wake_function(struct wait_queue_entry *curr, unsigned int mode,
                            int wake_flags, void *key)
{
        struct io_wait_queue *iowq = container_of(curr, struct io_wait_queue, wq);

        /*
         * Cannot safely flush overflowed CQEs from here, ensure we wake up
         * the task, and the next invocation will do it.
         */
        if (io_should_wake(iowq) || io_has_work(iowq->ctx))
                return autoremove_wake_function(curr, mode, wake_flags, key);
        return -1;
}

int io_run_task_work_sig(struct io_ring_ctx *ctx)
{
        if (!llist_empty(&ctx->work_llist)) {
                __set_current_state(TASK_RUNNING);
                if (io_run_local_work(ctx) > 0)
                        return 1;
        }
        if (io_run_task_work() > 0)
                return 1;
        if (task_sigpending(current))
                return -EINTR;
        return 0;
}

/* when returns >0, the caller should retry */
static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
                                          struct io_wait_queue *iowq)
{
        if (unlikely(READ_ONCE(ctx->check_cq)))
                return 1;
        if (unlikely(!llist_empty(&ctx->work_llist)))
                return 1;
        if (unlikely(test_thread_flag(TIF_NOTIFY_SIGNAL)))
                return 1;
        if (unlikely(task_sigpending(current)))
                return -EINTR;
        if (unlikely(io_should_wake(iowq)))
                return 0;
        if (iowq->timeout == KTIME_MAX)
                schedule();
        else if (!schedule_hrtimeout(&iowq->timeout, HRTIMER_MODE_ABS))
                return -ETIME;
        return 0;
}

/*
 * Wait until events become available, if we don't already have some. The
 * application must reap them itself, as they reside on the shared cq ring.
 */
static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
                          const sigset_t __user *sig, size_t sigsz,
                          struct __kernel_timespec __user *uts)
{
        struct io_wait_queue iowq;
        struct io_rings *rings = ctx->rings;
        int ret;

        if (!io_allowed_run_tw(ctx))
                return -EEXIST;
        if (!llist_empty(&ctx->work_llist))
                io_run_local_work(ctx);
        io_run_task_work();
        io_cqring_overflow_flush(ctx);
        /* if user messes with these they will just get an early return */
        if (__io_cqring_events_user(ctx) >= min_events)
                return 0;

        if (sig) {
#ifdef CONFIG_COMPAT
                if (in_compat_syscall())
                        ret = set_compat_user_sigmask((const compat_sigset_t __user *)sig,
                                                      sigsz);
                else
#endif
                        ret = set_user_sigmask(sig, sigsz);

                if (ret)
                        return ret;
        }

        init_waitqueue_func_entry(&iowq.wq, io_wake_function);
        iowq.wq.private = current;
        INIT_LIST_HEAD(&iowq.wq.entry);
        iowq.ctx = ctx;
        iowq.nr_timeouts = atomic_read(&ctx->cq_timeouts);
        iowq.cq_tail = READ_ONCE(ctx->rings->cq.head) + min_events;
        iowq.timeout = KTIME_MAX;

        if (uts) {
                struct timespec64 ts;

                if (get_timespec64(&ts, uts))
                        return -EFAULT;
                iowq.timeout = ktime_add_ns(timespec64_to_ktime(ts), ktime_get_ns());
        }

        trace_io_uring_cqring_wait(ctx, min_events);
        do {
                unsigned long check_cq;

                if (ctx->flags & IORING_SETUP_DEFER_TASKRUN) {
                        int nr_wait = (int) iowq.cq_tail - READ_ONCE(ctx->rings->cq.tail);

                        atomic_set(&ctx->cq_wait_nr, nr_wait);
                        set_current_state(TASK_INTERRUPTIBLE);
                } else {
                        prepare_to_wait_exclusive(&ctx->cq_wait, &iowq.wq,
                                                        TASK_INTERRUPTIBLE);
                }

                ret = io_cqring_wait_schedule(ctx, &iowq);
                __set_current_state(TASK_RUNNING);
                atomic_set(&ctx->cq_wait_nr, 0);

                if (ret < 0)
                        break;
                /*
                 * Run task_work after scheduling and before io_should_wake().
                 * If we got woken because of task_work being processed, run it
                 * now rather than let the caller do another wait loop.
                 */
                io_run_task_work();
                if (!llist_empty(&ctx->work_llist))
                        io_run_local_work(ctx);

                check_cq = READ_ONCE(ctx->check_cq);
                if (unlikely(check_cq)) {
                        /* let the caller flush overflows, retry */
                        if (check_cq & BIT(IO_CHECK_CQ_OVERFLOW_BIT))
                                io_cqring_do_overflow_flush(ctx);
                        if (check_cq & BIT(IO_CHECK_CQ_DROPPED_BIT)) {
                                ret = -EBADR;
                                break;
                        }
                }

                if (io_should_wake(&iowq)) {
                        ret = 0;
                        break;
                }
                cond_resched();
        } while (1);

        if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
                finish_wait(&ctx->cq_wait, &iowq.wq);
        restore_saved_sigmask_unless(ret == -EINTR);

        return READ_ONCE(rings->cq.head) == READ_ONCE(rings->cq.tail) ? ret : 0;
}

static void io_mem_free(void *ptr)
{
        struct page *page;

        if (!ptr)
                return;

        page = virt_to_head_page(ptr);
        if (put_page_testzero(page))
                free_compound_page(page);
}

static void *io_mem_alloc(size_t size)
{
        gfp_t gfp = GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP;

        return (void *) __get_free_pages(gfp, get_order(size));
}

static unsigned long rings_size(struct io_ring_ctx *ctx, unsigned int sq_entries,
                                unsigned int cq_entries, size_t *sq_offset)
{
        struct io_rings *rings;
        size_t off, sq_array_size;

        off = struct_size(rings, cqes, cq_entries);
        if (off == SIZE_MAX)
                return SIZE_MAX;
        if (ctx->flags & IORING_SETUP_CQE32) {
                if (check_shl_overflow(off, 1, &off))
                        return SIZE_MAX;
        }

#ifdef CONFIG_SMP
        off = ALIGN(off, SMP_CACHE_BYTES);
        if (off == 0)
                return SIZE_MAX;
#endif

        if (sq_offset)
                *sq_offset = off;

        sq_array_size = array_size(sizeof(u32), sq_entries);
        if (sq_array_size == SIZE_MAX)
                return SIZE_MAX;

        if (check_add_overflow(off, sq_array_size, &off))
                return SIZE_MAX;

        return off;
}

static int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg,
                               unsigned int eventfd_async)
{
        struct io_ev_fd *ev_fd;
        __s32 __user *fds = arg;
        int fd;

        ev_fd = rcu_dereference_protected(ctx->io_ev_fd,
                                        lockdep_is_held(&ctx->uring_lock));
        if (ev_fd)
                return -EBUSY;

        if (copy_from_user(&fd, fds, sizeof(*fds)))
                return -EFAULT;

        ev_fd = kmalloc(sizeof(*ev_fd), GFP_KERNEL);
        if (!ev_fd)
                return -ENOMEM;

        ev_fd->cq_ev_fd = eventfd_ctx_fdget(fd);
        if (IS_ERR(ev_fd->cq_ev_fd)) {
                int ret = PTR_ERR(ev_fd->cq_ev_fd);
                kfree(ev_fd);
                return ret;
        }

        spin_lock(&ctx->completion_lock);
        ctx->evfd_last_cq_tail = ctx->cached_cq_tail;
        spin_unlock(&ctx->completion_lock);

        ev_fd->eventfd_async = eventfd_async;
        ctx->has_evfd = true;
        rcu_assign_pointer(ctx->io_ev_fd, ev_fd);
        atomic_set(&ev_fd->refs, 1);
        atomic_set(&ev_fd->ops, 0);
        return 0;
}

static int io_eventfd_unregister(struct io_ring_ctx *ctx)
{
        struct io_ev_fd *ev_fd;

        ev_fd = rcu_dereference_protected(ctx->io_ev_fd,
                                        lockdep_is_held(&ctx->uring_lock));
        if (ev_fd) {
                ctx->has_evfd = false;
                rcu_assign_pointer(ctx->io_ev_fd, NULL);
                if (!atomic_fetch_or(BIT(IO_EVENTFD_OP_FREE_BIT), &ev_fd->ops))
                        call_rcu(&ev_fd->rcu, io_eventfd_ops);
                return 0;
        }

        return -ENXIO;
}

static void io_req_caches_free(struct io_ring_ctx *ctx)
{
        struct io_kiocb *req;
        int nr = 0;

        mutex_lock(&ctx->uring_lock);
        io_flush_cached_locked_reqs(ctx, &ctx->submit_state);

        while (!io_req_cache_empty(ctx)) {
                req = io_extract_req(ctx);
                kmem_cache_free(req_cachep, req);
                nr++;
        }
        if (nr)
                percpu_ref_put_many(&ctx->refs, nr);
        mutex_unlock(&ctx->uring_lock);
}

static void io_rsrc_node_cache_free(struct io_cache_entry *entry)
{
        kfree(container_of(entry, struct io_rsrc_node, cache));
}

static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
{
        io_sq_thread_finish(ctx);
        /* __io_rsrc_put_work() may need uring_lock to progress, wait w/o it */
        io_wait_rsrc_data(ctx->buf_data);
        io_wait_rsrc_data(ctx->file_data);

        mutex_lock(&ctx->uring_lock);
        if (ctx->buf_data)
                __io_sqe_buffers_unregister(ctx);
        if (ctx->file_data)
                __io_sqe_files_unregister(ctx);
        io_cqring_overflow_kill(ctx);
        io_eventfd_unregister(ctx);
        io_alloc_cache_free(&ctx->apoll_cache, io_apoll_cache_free);
        io_alloc_cache_free(&ctx->netmsg_cache, io_netmsg_cache_free);
        mutex_unlock(&ctx->uring_lock);
        io_destroy_buffers(ctx);
        if (ctx->sq_creds)
                put_cred(ctx->sq_creds);
        if (ctx->submitter_task)
                put_task_struct(ctx->submitter_task);

        /* there are no registered resources left, nobody uses it */
        if (ctx->rsrc_node)
                io_rsrc_node_destroy(ctx, ctx->rsrc_node);
        if (ctx->rsrc_backup_node)
                io_rsrc_node_destroy(ctx, ctx->rsrc_backup_node);

        WARN_ON_ONCE(!list_empty(&ctx->rsrc_ref_list));

#if defined(CONFIG_UNIX)
        if (ctx->ring_sock) {
                ctx->ring_sock->file = NULL; /* so that iput() is called */
                sock_release(ctx->ring_sock);
        }
#endif
        WARN_ON_ONCE(!list_empty(&ctx->ltimeout_list));

        io_alloc_cache_free(&ctx->rsrc_node_cache, io_rsrc_node_cache_free);
        if (ctx->mm_account) {
                mmdrop(ctx->mm_account);
                ctx->mm_account = NULL;
        }
        io_mem_free(ctx->rings);
        io_mem_free(ctx->sq_sqes);

        percpu_ref_exit(&ctx->refs);
        free_uid(ctx->user);
        io_req_caches_free(ctx);
        if (ctx->hash_map)
                io_wq_put_hash(ctx->hash_map);
        kfree(ctx->cancel_table.hbs);
        kfree(ctx->cancel_table_locked.hbs);
        kfree(ctx->dummy_ubuf);
        kfree(ctx->io_bl);
        xa_destroy(&ctx->io_bl_xa);
        kfree(ctx);
}

static __cold void io_activate_pollwq_cb(struct callback_head *cb)
{
        struct io_ring_ctx *ctx = container_of(cb, struct io_ring_ctx,
                                               poll_wq_task_work);

        mutex_lock(&ctx->uring_lock);
        ctx->poll_activated = true;
        mutex_unlock(&ctx->uring_lock);

        /*
         * Wake ups for some events between start of polling and activation
         * might've been lost due to loose synchronisation.
         */
        wake_up_all(&ctx->poll_wq);
        percpu_ref_put(&ctx->refs);
}

static __cold void io_activate_pollwq(struct io_ring_ctx *ctx)
{
        spin_lock(&ctx->completion_lock);
        /* already activated or in progress */
        if (ctx->poll_activated || ctx->poll_wq_task_work.func)
                goto out;
        if (WARN_ON_ONCE(!ctx->task_complete))
                goto out;
        if (!ctx->submitter_task)
                goto out;
        /*
         * with ->submitter_task only the submitter task completes requests, we
         * only need to sync with it, which is done by injecting a tw
         */
        init_task_work(&ctx->poll_wq_task_work, io_activate_pollwq_cb);
        percpu_ref_get(&ctx->refs);
        if (task_work_add(ctx->submitter_task, &ctx->poll_wq_task_work, TWA_SIGNAL))
                percpu_ref_put(&ctx->refs);
out:
        spin_unlock(&ctx->completion_lock);
}

static __poll_t io_uring_poll(struct file *file, poll_table *wait)
{
        struct io_ring_ctx *ctx = file->private_data;
        __poll_t mask = 0;

        if (unlikely(!ctx->poll_activated))
                io_activate_pollwq(ctx);

        poll_wait(file, &ctx->poll_wq, wait);
        /*
         * synchronizes with barrier from wq_has_sleeper call in
         * io_commit_cqring
         */
        smp_rmb();
        if (!io_sqring_full(ctx))
                mask |= EPOLLOUT | EPOLLWRNORM;

        /*
         * Don't flush cqring overflow list here, just do a simple check.
         * Otherwise there could possible be ABBA deadlock:
         *      CPU0                    CPU1
         *      ----                    ----
         * lock(&ctx->uring_lock);
         *                              lock(&ep->mtx);
         *                              lock(&ctx->uring_lock);
         * lock(&ep->mtx);
         *
         * Users may get EPOLLIN meanwhile seeing nothing in cqring, this
         * pushes them to do the flush.
         */

        if (__io_cqring_events_user(ctx) || io_has_work(ctx))
                mask |= EPOLLIN | EPOLLRDNORM;

        return mask;
}

static int io_unregister_personality(struct io_ring_ctx *ctx, unsigned id)
{
        const struct cred *creds;

        creds = xa_erase(&ctx->personalities, id);
        if (creds) {
                put_cred(creds);
                return 0;
        }

        return -EINVAL;
}

struct io_tctx_exit {
        struct callback_head            task_work;
        struct completion               completion;
        struct io_ring_ctx              *ctx;
};

static __cold void io_tctx_exit_cb(struct callback_head *cb)
{
        struct io_uring_task *tctx = current->io_uring;
        struct io_tctx_exit *work;

        work = container_of(cb, struct io_tctx_exit, task_work);
        /*
         * When @in_cancel, we're in cancellation and it's racy to remove the
         * node. It'll be removed by the end of cancellation, just ignore it.
         * tctx can be NULL if the queueing of this task_work raced with
         * work cancelation off the exec path.
         */
        if (tctx && !atomic_read(&tctx->in_cancel))
                io_uring_del_tctx_node((unsigned long)work->ctx);
        complete(&work->completion);
}

static __cold bool io_cancel_ctx_cb(struct io_wq_work *work, void *data)
{
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);

        return req->ctx == data;
}

static __cold void io_ring_exit_work(struct work_struct *work)
{
        struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx, exit_work);
        unsigned long timeout = jiffies + HZ * 60 * 5;
        unsigned long interval = HZ / 20;
        struct io_tctx_exit exit;
        struct io_tctx_node *node;
        int ret;

        /*
         * If we're doing polled IO and end up having requests being
         * submitted async (out-of-line), then completions can come in while
         * we're waiting for refs to drop. We need to reap these manually,
         * as nobody else will be looking for them.
         */
        do {
                if (test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq)) {
                        mutex_lock(&ctx->uring_lock);
                        io_cqring_overflow_kill(ctx);
                        mutex_unlock(&ctx->uring_lock);
                }

                if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
                        io_move_task_work_from_local(ctx);

                while (io_uring_try_cancel_requests(ctx, NULL, true))
                        cond_resched();

                if (ctx->sq_data) {
                        struct io_sq_data *sqd = ctx->sq_data;
                        struct task_struct *tsk;

                        io_sq_thread_park(sqd);
                        tsk = sqd->thread;
                        if (tsk && tsk->io_uring && tsk->io_uring->io_wq)
                                io_wq_cancel_cb(tsk->io_uring->io_wq,
                                                io_cancel_ctx_cb, ctx, true);
                        io_sq_thread_unpark(sqd);
                }

                io_req_caches_free(ctx);

                if (WARN_ON_ONCE(time_after(jiffies, timeout))) {
                        /* there is little hope left, don't run it too often */
                        interval = HZ * 60;
                }
        } while (!wait_for_completion_timeout(&ctx->ref_comp, interval));

        init_completion(&exit.completion);
        init_task_work(&exit.task_work, io_tctx_exit_cb);
        exit.ctx = ctx;
        /*
         * Some may use context even when all refs and requests have been put,
         * and they are free to do so while still holding uring_lock or
         * completion_lock, see io_req_task_submit(). Apart from other work,
         * this lock/unlock section also waits them to finish.
         */
        mutex_lock(&ctx->uring_lock);
        while (!list_empty(&ctx->tctx_list)) {
                WARN_ON_ONCE(time_after(jiffies, timeout));

                node = list_first_entry(&ctx->tctx_list, struct io_tctx_node,
                                        ctx_node);
                /* don't spin on a single task if cancellation failed */
                list_rotate_left(&ctx->tctx_list);
                ret = task_work_add(node->task, &exit.task_work, TWA_SIGNAL);
                if (WARN_ON_ONCE(ret))
                        continue;

                mutex_unlock(&ctx->uring_lock);
                wait_for_completion(&exit.completion);
                mutex_lock(&ctx->uring_lock);
        }
        mutex_unlock(&ctx->uring_lock);
        spin_lock(&ctx->completion_lock);
        spin_unlock(&ctx->completion_lock);

        /* pairs with RCU read section in io_req_local_work_add() */
        if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
                synchronize_rcu();

        io_ring_ctx_free(ctx);
}

static __cold void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
{
        unsigned long index;
        struct creds *creds;

        mutex_lock(&ctx->uring_lock);
        percpu_ref_kill(&ctx->refs);
        xa_for_each(&ctx->personalities, index, creds)
                io_unregister_personality(ctx, index);
        if (ctx->rings)
                io_poll_remove_all(ctx, NULL, true);
        mutex_unlock(&ctx->uring_lock);

        /*
         * If we failed setting up the ctx, we might not have any rings
         * and therefore did not submit any requests
         */
        if (ctx->rings)
                io_kill_timeouts(ctx, NULL, true);

        INIT_WORK(&ctx->exit_work, io_ring_exit_work);
        /*
         * Use system_unbound_wq to avoid spawning tons of event kworkers
         * if we're exiting a ton of rings at the same time. It just adds
         * noise and overhead, there's no discernable change in runtime
         * over using system_wq.
         */
        queue_work(system_unbound_wq, &ctx->exit_work);
}

static int io_uring_release(struct inode *inode, struct file *file)
{
        struct io_ring_ctx *ctx = file->private_data;

        file->private_data = NULL;
        io_ring_ctx_wait_and_kill(ctx);
        return 0;
}

struct io_task_cancel {
        struct task_struct *task;
        bool all;
};

static bool io_cancel_task_cb(struct io_wq_work *work, void *data)
{
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);
        struct io_task_cancel *cancel = data;

        return io_match_task_safe(req, cancel->task, cancel->all);
}

static __cold bool io_cancel_defer_files(struct io_ring_ctx *ctx,
                                         struct task_struct *task,
                                         bool cancel_all)
{
        struct io_defer_entry *de;
        LIST_HEAD(list);

        spin_lock(&ctx->completion_lock);
        list_for_each_entry_reverse(de, &ctx->defer_list, list) {
                if (io_match_task_safe(de->req, task, cancel_all)) {
                        list_cut_position(&list, &ctx->defer_list, &de->list);
                        break;
                }
        }
        spin_unlock(&ctx->completion_lock);
        if (list_empty(&list))
                return false;

        while (!list_empty(&list)) {
                de = list_first_entry(&list, struct io_defer_entry, list);
                list_del_init(&de->list);
                io_req_task_queue_fail(de->req, -ECANCELED);
                kfree(de);
        }
        return true;
}

static __cold bool io_uring_try_cancel_iowq(struct io_ring_ctx *ctx)
{
        struct io_tctx_node *node;
        enum io_wq_cancel cret;
        bool ret = false;

        mutex_lock(&ctx->uring_lock);
        list_for_each_entry(node, &ctx->tctx_list, ctx_node) {
                struct io_uring_task *tctx = node->task->io_uring;

                /*
                 * io_wq will stay alive while we hold uring_lock, because it's
                 * killed after ctx nodes, which requires to take the lock.
                 */
                if (!tctx || !tctx->io_wq)
                        continue;
                cret = io_wq_cancel_cb(tctx->io_wq, io_cancel_ctx_cb, ctx, true);
                ret |= (cret != IO_WQ_CANCEL_NOTFOUND);
        }
        mutex_unlock(&ctx->uring_lock);

        return ret;
}

static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
                                                struct task_struct *task,
                                                bool cancel_all)
{
        struct io_task_cancel cancel = { .task = task, .all = cancel_all, };
        struct io_uring_task *tctx = task ? task->io_uring : NULL;
        enum io_wq_cancel cret;
        bool ret = false;

        /* failed during ring init, it couldn't have issued any requests */
        if (!ctx->rings)
                return false;

        if (!task) {
                ret |= io_uring_try_cancel_iowq(ctx);
        } else if (tctx && tctx->io_wq) {
                /*
                 * Cancels requests of all rings, not only @ctx, but
                 * it's fine as the task is in exit/exec.
                 */
                cret = io_wq_cancel_cb(tctx->io_wq, io_cancel_task_cb,
                                       &cancel, true);
                ret |= (cret != IO_WQ_CANCEL_NOTFOUND);
        }

        /* SQPOLL thread does its own polling */
        if ((!(ctx->flags & IORING_SETUP_SQPOLL) && cancel_all) ||
            (ctx->sq_data && ctx->sq_data->thread == current)) {
                while (!wq_list_empty(&ctx->iopoll_list)) {
                        io_iopoll_try_reap_events(ctx);
                        ret = true;
                        cond_resched();
                }
        }

        if ((ctx->flags & IORING_SETUP_DEFER_TASKRUN) &&
            io_allowed_defer_tw_run(ctx))
                ret |= io_run_local_work(ctx) > 0;
        ret |= io_cancel_defer_files(ctx, task, cancel_all);
        mutex_lock(&ctx->uring_lock);
        ret |= io_poll_remove_all(ctx, task, cancel_all);
        mutex_unlock(&ctx->uring_lock);
        ret |= io_kill_timeouts(ctx, task, cancel_all);
        if (task)
                ret |= io_run_task_work() > 0;
        return ret;
}

static s64 tctx_inflight(struct io_uring_task *tctx, bool tracked)
{
        if (tracked)
                return atomic_read(&tctx->inflight_tracked);
        return percpu_counter_sum(&tctx->inflight);
}

/*
 * Find any io_uring ctx that this task has registered or done IO on, and cancel
 * requests. @sqd should be not-null IFF it's an SQPOLL thread cancellation.
 */
__cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
{
        struct io_uring_task *tctx = current->io_uring;
        struct io_ring_ctx *ctx;
        s64 inflight;
        DEFINE_WAIT(wait);

        WARN_ON_ONCE(sqd && sqd->thread != current);

        if (!current->io_uring)
                return;
        if (tctx->io_wq)
                io_wq_exit_start(tctx->io_wq);

        atomic_inc(&tctx->in_cancel);
        do {
                bool loop = false;

                io_uring_drop_tctx_refs(current);
                /* read completions before cancelations */
                inflight = tctx_inflight(tctx, !cancel_all);
                if (!inflight)
                        break;

                if (!sqd) {
                        struct io_tctx_node *node;
                        unsigned long index;

                        xa_for_each(&tctx->xa, index, node) {
                                /* sqpoll task will cancel all its requests */
                                if (node->ctx->sq_data)
                                        continue;
                                loop |= io_uring_try_cancel_requests(node->ctx,
                                                        current, cancel_all);
                        }
                } else {
                        list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
                                loop |= io_uring_try_cancel_requests(ctx,
                                                                     current,
                                                                     cancel_all);
                }

                if (loop) {
                        cond_resched();
                        continue;
                }

                prepare_to_wait(&tctx->wait, &wait, TASK_INTERRUPTIBLE);
                io_run_task_work();
                io_uring_drop_tctx_refs(current);

                /*
                 * If we've seen completions, retry without waiting. This
                 * avoids a race where a completion comes in before we did
                 * prepare_to_wait().
                 */
                if (inflight == tctx_inflight(tctx, !cancel_all))
                        schedule();
                finish_wait(&tctx->wait, &wait);
        } while (1);

        io_uring_clean_tctx(tctx);
        if (cancel_all) {
                /*
                 * We shouldn't run task_works after cancel, so just leave
                 * ->in_cancel set for normal exit.
                 */
                atomic_dec(&tctx->in_cancel);
                /* for exec all current's requests should be gone, kill tctx */
                __io_uring_free(current);
        }
}

void __io_uring_cancel(bool cancel_all)
{
        io_uring_cancel_generic(cancel_all, NULL);
}

static void *io_uring_validate_mmap_request(struct file *file,
                                            loff_t pgoff, size_t sz)
{
        struct io_ring_ctx *ctx = file->private_data;
        loff_t offset = pgoff << PAGE_SHIFT;
        struct page *page;
        void *ptr;

        switch (offset & IORING_OFF_MMAP_MASK) {
        case IORING_OFF_SQ_RING:
        case IORING_OFF_CQ_RING:
                ptr = ctx->rings;
                break;
        case IORING_OFF_SQES:
                ptr = ctx->sq_sqes;
                break;
        case IORING_OFF_PBUF_RING: {
                unsigned int bgid;

                bgid = (offset & ~IORING_OFF_MMAP_MASK) >> IORING_OFF_PBUF_SHIFT;
                mutex_lock(&ctx->uring_lock);
                ptr = io_pbuf_get_address(ctx, bgid);
                mutex_unlock(&ctx->uring_lock);
                if (!ptr)
                        return ERR_PTR(-EINVAL);
                break;
                }
        default:
                return ERR_PTR(-EINVAL);
        }

        page = virt_to_head_page(ptr);
        if (sz > page_size(page))
                return ERR_PTR(-EINVAL);

        return ptr;
}

#ifdef CONFIG_MMU

static __cold int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
{
        size_t sz = vma->vm_end - vma->vm_start;
        unsigned long pfn;
        void *ptr;

        ptr = io_uring_validate_mmap_request(file, vma->vm_pgoff, sz);
        if (IS_ERR(ptr))
                return PTR_ERR(ptr);

        pfn = virt_to_phys(ptr) >> PAGE_SHIFT;
        return remap_pfn_range(vma, vma->vm_start, pfn, sz, vma->vm_page_prot);
}

static unsigned long io_uring_mmu_get_unmapped_area(struct file *filp,
                        unsigned long addr, unsigned long len,
                        unsigned long pgoff, unsigned long flags)
{
        const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
        struct vm_unmapped_area_info info;
        void *ptr;

        /*
         * Do not allow to map to user-provided address to avoid breaking the
         * aliasing rules. Userspace is not able to guess the offset address of
         * kernel kmalloc()ed memory area.
         */
        if (addr)
                return -EINVAL;

        ptr = io_uring_validate_mmap_request(filp, pgoff, len);
        if (IS_ERR(ptr))
                return -ENOMEM;

        info.flags = VM_UNMAPPED_AREA_TOPDOWN;
        info.length = len;
        info.low_limit = max(PAGE_SIZE, mmap_min_addr);
        info.high_limit = arch_get_mmap_base(addr, current->mm->mmap_base);
#ifdef SHM_COLOUR
        info.align_mask = PAGE_MASK & (SHM_COLOUR - 1UL);
#else
        info.align_mask = PAGE_MASK & (SHMLBA - 1UL);
#endif
        info.align_offset = (unsigned long) ptr;

        /*
         * A failed mmap() very likely causes application failure,
         * so fall back to the bottom-up function here. This scenario
         * can happen with large stack limits and large mmap()
         * allocations.
         */
        addr = vm_unmapped_area(&info);
        if (offset_in_page(addr)) {
                info.flags = 0;
                info.low_limit = TASK_UNMAPPED_BASE;
                info.high_limit = mmap_end;
                addr = vm_unmapped_area(&info);
        }

        return addr;
}

#else /* !CONFIG_MMU */

static int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
{
        return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -EINVAL;
}

static unsigned int io_uring_nommu_mmap_capabilities(struct file *file)
{
        return NOMMU_MAP_DIRECT | NOMMU_MAP_READ | NOMMU_MAP_WRITE;
}

static unsigned long io_uring_nommu_get_unmapped_area(struct file *file,
        unsigned long addr, unsigned long len,
        unsigned long pgoff, unsigned long flags)
{
        void *ptr;

        ptr = io_uring_validate_mmap_request(file, pgoff, len);
        if (IS_ERR(ptr))
                return PTR_ERR(ptr);

        return (unsigned long) ptr;
}

#endif /* !CONFIG_MMU */

static int io_validate_ext_arg(unsigned flags, const void __user *argp, size_t argsz)
{
        if (flags & IORING_ENTER_EXT_ARG) {
                struct io_uring_getevents_arg arg;

                if (argsz != sizeof(arg))
                        return -EINVAL;
                if (copy_from_user(&arg, argp, sizeof(arg)))
                        return -EFAULT;
        }
        return 0;
}

static int io_get_ext_arg(unsigned flags, const void __user *argp, size_t *argsz,
                          struct __kernel_timespec __user **ts,
                          const sigset_t __user **sig)
{
        struct io_uring_getevents_arg arg;

        /*
         * If EXT_ARG isn't set, then we have no timespec and the argp pointer
         * is just a pointer to the sigset_t.
         */
        if (!(flags & IORING_ENTER_EXT_ARG)) {
                *sig = (const sigset_t __user *) argp;
                *ts = NULL;
                return 0;
        }

        /*
         * EXT_ARG is set - ensure we agree on the size of it and copy in our
         * timespec and sigset_t pointers if good.
         */
        if (*argsz != sizeof(arg))
                return -EINVAL;
        if (copy_from_user(&arg, argp, sizeof(arg)))
                return -EFAULT;
        if (arg.pad)
                return -EINVAL;
        *sig = u64_to_user_ptr(arg.sigmask);
        *argsz = arg.sigmask_sz;
        *ts = u64_to_user_ptr(arg.ts);
        return 0;
}

SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
                u32, min_complete, u32, flags, const void __user *, argp,
                size_t, argsz)
{
        struct io_ring_ctx *ctx;
        struct fd f;
        long ret;

        if (unlikely(flags & ~(IORING_ENTER_GETEVENTS | IORING_ENTER_SQ_WAKEUP |
                               IORING_ENTER_SQ_WAIT | IORING_ENTER_EXT_ARG |
                               IORING_ENTER_REGISTERED_RING)))
                return -EINVAL;

        /*
         * Ring fd has been registered via IORING_REGISTER_RING_FDS, we
         * need only dereference our task private array to find it.
         */
        if (flags & IORING_ENTER_REGISTERED_RING) {
                struct io_uring_task *tctx = current->io_uring;

                if (unlikely(!tctx || fd >= IO_RINGFD_REG_MAX))
                        return -EINVAL;
                fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
                f.file = tctx->registered_rings[fd];
                f.flags = 0;
                if (unlikely(!f.file))
                        return -EBADF;
        } else {
                f = fdget(fd);
                if (unlikely(!f.file))
                        return -EBADF;
                ret = -EOPNOTSUPP;
                if (unlikely(!io_is_uring_fops(f.file)))
                        goto out;
        }

        ctx = f.file->private_data;
        ret = -EBADFD;
        if (unlikely(ctx->flags & IORING_SETUP_R_DISABLED))
                goto out;

        /*
         * For SQ polling, the thread will do all submissions and completions.
         * Just return the requested submit count, and wake the thread if
         * we were asked to.
         */
        ret = 0;
        if (ctx->flags & IORING_SETUP_SQPOLL) {
                io_cqring_overflow_flush(ctx);

                if (unlikely(ctx->sq_data->thread == NULL)) {
                        ret = -EOWNERDEAD;
                        goto out;
                }
                if (flags & IORING_ENTER_SQ_WAKEUP)
                        wake_up(&ctx->sq_data->wait);
                if (flags & IORING_ENTER_SQ_WAIT)
                        io_sqpoll_wait_sq(ctx);

                ret = to_submit;
        } else if (to_submit) {
                ret = io_uring_add_tctx_node(ctx);
                if (unlikely(ret))
                        goto out;

                mutex_lock(&ctx->uring_lock);
                ret = io_submit_sqes(ctx, to_submit);
                if (ret != to_submit) {
                        mutex_unlock(&ctx->uring_lock);
                        goto out;
                }
                if (flags & IORING_ENTER_GETEVENTS) {
                        if (ctx->syscall_iopoll)
                                goto iopoll_locked;
                        /*
                         * Ignore errors, we'll soon call io_cqring_wait() and
                         * it should handle ownership problems if any.
                         */
                        if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
                                (void)io_run_local_work_locked(ctx);
                }
                mutex_unlock(&ctx->uring_lock);
        }

        if (flags & IORING_ENTER_GETEVENTS) {
                int ret2;

                if (ctx->syscall_iopoll) {
                        /*
                         * We disallow the app entering submit/complete with
                         * polling, but we still need to lock the ring to
                         * prevent racing with polled issue that got punted to
                         * a workqueue.
                         */
                        mutex_lock(&ctx->uring_lock);
iopoll_locked:
                        ret2 = io_validate_ext_arg(flags, argp, argsz);
                        if (likely(!ret2)) {
                                min_complete = min(min_complete,
                                                   ctx->cq_entries);
                                ret2 = io_iopoll_check(ctx, min_complete);
                        }
                        mutex_unlock(&ctx->uring_lock);
                } else {
                        const sigset_t __user *sig;
                        struct __kernel_timespec __user *ts;

                        ret2 = io_get_ext_arg(flags, argp, &argsz, &ts, &sig);
                        if (likely(!ret2)) {
                                min_complete = min(min_complete,
                                                   ctx->cq_entries);
                                ret2 = io_cqring_wait(ctx, min_complete, sig,
                                                      argsz, ts);
                        }
                }

                if (!ret) {
                        ret = ret2;

                        /*
                         * EBADR indicates that one or more CQE were dropped.
                         * Once the user has been informed we can clear the bit
                         * as they are obviously ok with those drops.
                         */
                        if (unlikely(ret2 == -EBADR))
                                clear_bit(IO_CHECK_CQ_DROPPED_BIT,
                                          &ctx->check_cq);
                }
        }
out:
        fdput(f);
        return ret;
}

static const struct file_operations io_uring_fops = {
        .release        = io_uring_release,
        .mmap           = io_uring_mmap,
#ifndef CONFIG_MMU
        .get_unmapped_area = io_uring_nommu_get_unmapped_area,
        .mmap_capabilities = io_uring_nommu_mmap_capabilities,
#else
        .get_unmapped_area = io_uring_mmu_get_unmapped_area,
#endif
        .poll           = io_uring_poll,
#ifdef CONFIG_PROC_FS
        .show_fdinfo    = io_uring_show_fdinfo,
#endif
};

bool io_is_uring_fops(struct file *file)
{
        return file->f_op == &io_uring_fops;
}

static __cold int io_allocate_scq_urings(struct io_ring_ctx *ctx,
                                         struct io_uring_params *p)
{
        struct io_rings *rings;
        size_t size, sq_array_offset;

        /* make sure these are sane, as we already accounted them */
        ctx->sq_entries = p->sq_entries;
        ctx->cq_entries = p->cq_entries;

        size = rings_size(ctx, p->sq_entries, p->cq_entries, &sq_array_offset);
        if (size == SIZE_MAX)
                return -EOVERFLOW;

        rings = io_mem_alloc(size);
        if (!rings)
                return -ENOMEM;

        ctx->rings = rings;
        ctx->sq_array = (u32 *)((char *)rings + sq_array_offset);
        rings->sq_ring_mask = p->sq_entries - 1;
        rings->cq_ring_mask = p->cq_entries - 1;
        rings->sq_ring_entries = p->sq_entries;
        rings->cq_ring_entries = p->cq_entries;

        if (p->flags & IORING_SETUP_SQE128)
                size = array_size(2 * sizeof(struct io_uring_sqe), p->sq_entries);
        else
                size = array_size(sizeof(struct io_uring_sqe), p->sq_entries);
        if (size == SIZE_MAX) {
                io_mem_free(ctx->rings);
                ctx->rings = NULL;
                return -EOVERFLOW;
        }

        ctx->sq_sqes = io_mem_alloc(size);
        if (!ctx->sq_sqes) {
                io_mem_free(ctx->rings);
                ctx->rings = NULL;
                return -ENOMEM;
        }

        return 0;
}

static int io_uring_install_fd(struct io_ring_ctx *ctx, struct file *file)
{
        int ret, fd;

        fd = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
        if (fd < 0)
                return fd;

        ret = __io_uring_add_tctx_node(ctx);
        if (ret) {
                put_unused_fd(fd);
                return ret;
        }
        fd_install(fd, file);
        return fd;
}

/*
 * Allocate an anonymous fd, this is what constitutes the application
 * visible backing of an io_uring instance. The application mmaps this
 * fd to gain access to the SQ/CQ ring details. If UNIX sockets are enabled,
 * we have to tie this fd to a socket for file garbage collection purposes.
 */
static struct file *io_uring_get_file(struct io_ring_ctx *ctx)
{
        struct file *file;
#if defined(CONFIG_UNIX)
        int ret;

        ret = sock_create_kern(&init_net, PF_UNIX, SOCK_RAW, IPPROTO_IP,
                                &ctx->ring_sock);
        if (ret)
                return ERR_PTR(ret);
#endif

        file = anon_inode_getfile_secure("[io_uring]", &io_uring_fops, ctx,
                                         O_RDWR | O_CLOEXEC, NULL);
#if defined(CONFIG_UNIX)
        if (IS_ERR(file)) {
                sock_release(ctx->ring_sock);
                ctx->ring_sock = NULL;
        } else {
                ctx->ring_sock->file = file;
        }
#endif
        return file;
}

static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
                                  struct io_uring_params __user *params)
{
        struct io_ring_ctx *ctx;
        struct file *file;
        int ret;

        if (!entries)
                return -EINVAL;
        if (entries > IORING_MAX_ENTRIES) {
                if (!(p->flags & IORING_SETUP_CLAMP))
                        return -EINVAL;
                entries = IORING_MAX_ENTRIES;
        }

        /*
         * Use twice as many entries for the CQ ring. It's possible for the
         * application to drive a higher depth than the size of the SQ ring,
         * since the sqes are only used at submission time. This allows for
         * some flexibility in overcommitting a bit. If the application has
         * set IORING_SETUP_CQSIZE, it will have passed in the desired number
         * of CQ ring entries manually.
         */
        p->sq_entries = roundup_pow_of_two(entries);
        if (p->flags & IORING_SETUP_CQSIZE) {
                /*
                 * If IORING_SETUP_CQSIZE is set, we do the same roundup
                 * to a power-of-two, if it isn't already. We do NOT impose
                 * any cq vs sq ring sizing.
                 */
                if (!p->cq_entries)
                        return -EINVAL;
                if (p->cq_entries > IORING_MAX_CQ_ENTRIES) {
                        if (!(p->flags & IORING_SETUP_CLAMP))
                                return -EINVAL;
                        p->cq_entries = IORING_MAX_CQ_ENTRIES;
                }
                p->cq_entries = roundup_pow_of_two(p->cq_entries);
                if (p->cq_entries < p->sq_entries)
                        return -EINVAL;
        } else {
                p->cq_entries = 2 * p->sq_entries;
        }

        ctx = io_ring_ctx_alloc(p);
        if (!ctx)
                return -ENOMEM;

        if ((ctx->flags & IORING_SETUP_DEFER_TASKRUN) &&
            !(ctx->flags & IORING_SETUP_IOPOLL) &&
            !(ctx->flags & IORING_SETUP_SQPOLL))
                ctx->task_complete = true;

        /*
         * lazy poll_wq activation relies on ->task_complete for synchronisation
         * purposes, see io_activate_pollwq()
         */
        if (!ctx->task_complete)
                ctx->poll_activated = true;

        /*
         * When SETUP_IOPOLL and SETUP_SQPOLL are both enabled, user
         * space applications don't need to do io completion events
         * polling again, they can rely on io_sq_thread to do polling
         * work, which can reduce cpu usage and uring_lock contention.
         */
        if (ctx->flags & IORING_SETUP_IOPOLL &&
            !(ctx->flags & IORING_SETUP_SQPOLL))
                ctx->syscall_iopoll = 1;

        ctx->compat = in_compat_syscall();
        if (!capable(CAP_IPC_LOCK))
                ctx->user = get_uid(current_user());

        /*
         * For SQPOLL, we just need a wakeup, always. For !SQPOLL, if
         * COOP_TASKRUN is set, then IPIs are never needed by the app.
         */
        ret = -EINVAL;
        if (ctx->flags & IORING_SETUP_SQPOLL) {
                /* IPI related flags don't make sense with SQPOLL */
                if (ctx->flags & (IORING_SETUP_COOP_TASKRUN |
                                  IORING_SETUP_TASKRUN_FLAG |
                                  IORING_SETUP_DEFER_TASKRUN))
                        goto err;
                ctx->notify_method = TWA_SIGNAL_NO_IPI;
        } else if (ctx->flags & IORING_SETUP_COOP_TASKRUN) {
                ctx->notify_method = TWA_SIGNAL_NO_IPI;
        } else {
                if (ctx->flags & IORING_SETUP_TASKRUN_FLAG &&
                    !(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
                        goto err;
                ctx->notify_method = TWA_SIGNAL;
        }

        /*
         * For DEFER_TASKRUN we require the completion task to be the same as the
         * submission task. This implies that there is only one submitter, so enforce
         * that.
         */
        if (ctx->flags & IORING_SETUP_DEFER_TASKRUN &&
            !(ctx->flags & IORING_SETUP_SINGLE_ISSUER)) {
                goto err;
        }

        /*
         * This is just grabbed for accounting purposes. When a process exits,
         * the mm is exited and dropped before the files, hence we need to hang
         * on to this mm purely for the purposes of being able to unaccount
         * memory (locked/pinned vm). It's not used for anything else.
         */
        mmgrab(current->mm);
        ctx->mm_account = current->mm;

        ret = io_allocate_scq_urings(ctx, p);
        if (ret)
                goto err;

        ret = io_sq_offload_create(ctx, p);
        if (ret)
                goto err;
        /* always set a rsrc node */
        ret = io_rsrc_node_switch_start(ctx);
        if (ret)
                goto err;
        io_rsrc_node_switch(ctx, NULL);

        memset(&p->sq_off, 0, sizeof(p->sq_off));
        p->sq_off.head = offsetof(struct io_rings, sq.head);
        p->sq_off.tail = offsetof(struct io_rings, sq.tail);
        p->sq_off.ring_mask = offsetof(struct io_rings, sq_ring_mask);
        p->sq_off.ring_entries = offsetof(struct io_rings, sq_ring_entries);
        p->sq_off.flags = offsetof(struct io_rings, sq_flags);
        p->sq_off.dropped = offsetof(struct io_rings, sq_dropped);
        p->sq_off.array = (char *)ctx->sq_array - (char *)ctx->rings;

        memset(&p->cq_off, 0, sizeof(p->cq_off));
        p->cq_off.head = offsetof(struct io_rings, cq.head);
        p->cq_off.tail = offsetof(struct io_rings, cq.tail);
        p->cq_off.ring_mask = offsetof(struct io_rings, cq_ring_mask);
        p->cq_off.ring_entries = offsetof(struct io_rings, cq_ring_entries);
        p->cq_off.overflow = offsetof(struct io_rings, cq_overflow);
        p->cq_off.cqes = offsetof(struct io_rings, cqes);
        p->cq_off.flags = offsetof(struct io_rings, cq_flags);

        p->features = IORING_FEAT_SINGLE_MMAP | IORING_FEAT_NODROP |
                        IORING_FEAT_SUBMIT_STABLE | IORING_FEAT_RW_CUR_POS |
                        IORING_FEAT_CUR_PERSONALITY | IORING_FEAT_FAST_POLL |
                        IORING_FEAT_POLL_32BITS | IORING_FEAT_SQPOLL_NONFIXED |
                        IORING_FEAT_EXT_ARG | IORING_FEAT_NATIVE_WORKERS |
                        IORING_FEAT_RSRC_TAGS | IORING_FEAT_CQE_SKIP |
                        IORING_FEAT_LINKED_FILE | IORING_FEAT_REG_REG_RING;

        if (copy_to_user(params, p, sizeof(*p))) {
                ret = -EFAULT;
                goto err;
        }

        if (ctx->flags & IORING_SETUP_SINGLE_ISSUER
            && !(ctx->flags & IORING_SETUP_R_DISABLED))
                WRITE_ONCE(ctx->submitter_task, get_task_struct(current));

        file = io_uring_get_file(ctx);
        if (IS_ERR(file)) {
                ret = PTR_ERR(file);
                goto err;
        }

        /*
         * Install ring fd as the very last thing, so we don't risk someone
         * having closed it before we finish setup
         */
        ret = io_uring_install_fd(ctx, file);
        if (ret < 0) {
                /* fput will clean it up */
                fput(file);
                return ret;
        }

        trace_io_uring_create(ret, ctx, p->sq_entries, p->cq_entries, p->flags);
        return ret;
err:
        io_ring_ctx_wait_and_kill(ctx);
        return ret;
}

/*
 * Sets up an aio uring context, and returns the fd. Applications asks for a
 * ring size, we return the actual sq/cq ring sizes (among other things) in the
 * params structure passed in.
 */
static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
{
        struct io_uring_params p;
        int i;

        if (copy_from_user(&p, params, sizeof(p)))
                return -EFAULT;
        for (i = 0; i < ARRAY_SIZE(p.resv); i++) {
                if (p.resv[i])
                        return -EINVAL;
        }

        if (p.flags & ~(IORING_SETUP_IOPOLL | IORING_SETUP_SQPOLL |
                        IORING_SETUP_SQ_AFF | IORING_SETUP_CQSIZE |
                        IORING_SETUP_CLAMP | IORING_SETUP_ATTACH_WQ |
                        IORING_SETUP_R_DISABLED | IORING_SETUP_SUBMIT_ALL |
                        IORING_SETUP_COOP_TASKRUN | IORING_SETUP_TASKRUN_FLAG |
                        IORING_SETUP_SQE128 | IORING_SETUP_CQE32 |
                        IORING_SETUP_SINGLE_ISSUER | IORING_SETUP_DEFER_TASKRUN))
                return -EINVAL;

        return io_uring_create(entries, &p, params);
}

SYSCALL_DEFINE2(io_uring_setup, u32, entries,
                struct io_uring_params __user *, params)
{
        return io_uring_setup(entries, params);
}

static __cold int io_probe(struct io_ring_ctx *ctx, void __user *arg,
                           unsigned nr_args)
{
        struct io_uring_probe *p;
        size_t size;
        int i, ret;

        size = struct_size(p, ops, nr_args);
        if (size == SIZE_MAX)
                return -EOVERFLOW;
        p = kzalloc(size, GFP_KERNEL);
        if (!p)
                return -ENOMEM;

        ret = -EFAULT;
        if (copy_from_user(p, arg, size))
                goto out;
        ret = -EINVAL;
        if (memchr_inv(p, 0, size))
                goto out;

        p->last_op = IORING_OP_LAST - 1;
        if (nr_args > IORING_OP_LAST)
                nr_args = IORING_OP_LAST;

        for (i = 0; i < nr_args; i++) {
                p->ops[i].op = i;
                if (!io_issue_defs[i].not_supported)
                        p->ops[i].flags = IO_URING_OP_SUPPORTED;
        }
        p->ops_len = i;

        ret = 0;
        if (copy_to_user(arg, p, size))
                ret = -EFAULT;
out:
        kfree(p);
        return ret;
}

static int io_register_personality(struct io_ring_ctx *ctx)
{
        const struct cred *creds;
        u32 id;
        int ret;

        creds = get_current_cred();

        ret = xa_alloc_cyclic(&ctx->personalities, &id, (void *)creds,
                        XA_LIMIT(0, USHRT_MAX), &ctx->pers_next, GFP_KERNEL);
        if (ret < 0) {
                put_cred(creds);
                return ret;
        }
        return id;
}

static __cold int io_register_restrictions(struct io_ring_ctx *ctx,
                                           void __user *arg, unsigned int nr_args)
{
        struct io_uring_restriction *res;
        size_t size;
        int i, ret;

        /* Restrictions allowed only if rings started disabled */
        if (!(ctx->flags & IORING_SETUP_R_DISABLED))
                return -EBADFD;

        /* We allow only a single restrictions registration */
        if (ctx->restrictions.registered)
                return -EBUSY;

        if (!arg || nr_args > IORING_MAX_RESTRICTIONS)
                return -EINVAL;

        size = array_size(nr_args, sizeof(*res));
        if (size == SIZE_MAX)
                return -EOVERFLOW;

        res = memdup_user(arg, size);
        if (IS_ERR(res))
                return PTR_ERR(res);

        ret = 0;

        for (i = 0; i < nr_args; i++) {
                switch (res[i].opcode) {
                case IORING_RESTRICTION_REGISTER_OP:
                        if (res[i].register_op >= IORING_REGISTER_LAST) {
                                ret = -EINVAL;
                                goto out;
                        }

                        __set_bit(res[i].register_op,
                                  ctx->restrictions.register_op);
                        break;
                case IORING_RESTRICTION_SQE_OP:
                        if (res[i].sqe_op >= IORING_OP_LAST) {
                                ret = -EINVAL;
                                goto out;
                        }

                        __set_bit(res[i].sqe_op, ctx->restrictions.sqe_op);
                        break;
                case IORING_RESTRICTION_SQE_FLAGS_ALLOWED:
                        ctx->restrictions.sqe_flags_allowed = res[i].sqe_flags;
                        break;
                case IORING_RESTRICTION_SQE_FLAGS_REQUIRED:
                        ctx->restrictions.sqe_flags_required = res[i].sqe_flags;
                        break;
                default:
                        ret = -EINVAL;
                        goto out;
                }
        }

out:
        /* Reset all restrictions if an error happened */
        if (ret != 0)
                memset(&ctx->restrictions, 0, sizeof(ctx->restrictions));
        else
                ctx->restrictions.registered = true;

        kfree(res);
        return ret;
}

static int io_register_enable_rings(struct io_ring_ctx *ctx)
{
        if (!(ctx->flags & IORING_SETUP_R_DISABLED))
                return -EBADFD;

        if (ctx->flags & IORING_SETUP_SINGLE_ISSUER && !ctx->submitter_task) {
                WRITE_ONCE(ctx->submitter_task, get_task_struct(current));
                /*
                 * Lazy activation attempts would fail if it was polled before
                 * submitter_task is set.
                 */
                if (wq_has_sleeper(&ctx->poll_wq))
                        io_activate_pollwq(ctx);
        }

        if (ctx->restrictions.registered)
                ctx->restricted = 1;

        ctx->flags &= ~IORING_SETUP_R_DISABLED;
        if (ctx->sq_data && wq_has_sleeper(&ctx->sq_data->wait))
                wake_up(&ctx->sq_data->wait);
        return 0;
}

static __cold int io_register_iowq_aff(struct io_ring_ctx *ctx,
                                       void __user *arg, unsigned len)
{
        struct io_uring_task *tctx = current->io_uring;
        cpumask_var_t new_mask;
        int ret;

        if (!tctx || !tctx->io_wq)
                return -EINVAL;

        if (!alloc_cpumask_var(&new_mask, GFP_KERNEL))
                return -ENOMEM;

        cpumask_clear(new_mask);
        if (len > cpumask_size())
                len = cpumask_size();

        if (in_compat_syscall()) {
                ret = compat_get_bitmap(cpumask_bits(new_mask),
                                        (const compat_ulong_t __user *)arg,
                                        len * 8 /* CHAR_BIT */);
        } else {
                ret = copy_from_user(new_mask, arg, len);
        }

        if (ret) {
                free_cpumask_var(new_mask);
                return -EFAULT;
        }

        ret = io_wq_cpu_affinity(tctx->io_wq, new_mask);
        free_cpumask_var(new_mask);
        return ret;
}

static __cold int io_unregister_iowq_aff(struct io_ring_ctx *ctx)
{
        struct io_uring_task *tctx = current->io_uring;

        if (!tctx || !tctx->io_wq)
                return -EINVAL;

        return io_wq_cpu_affinity(tctx->io_wq, NULL);
}

static __cold int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
                                               void __user *arg)
        __must_hold(&ctx->uring_lock)
{
        struct io_tctx_node *node;
        struct io_uring_task *tctx = NULL;
        struct io_sq_data *sqd = NULL;
        __u32 new_count[2];
        int i, ret;

        if (copy_from_user(new_count, arg, sizeof(new_count)))
                return -EFAULT;
        for (i = 0; i < ARRAY_SIZE(new_count); i++)
                if (new_count[i] > INT_MAX)
                        return -EINVAL;

        if (ctx->flags & IORING_SETUP_SQPOLL) {
                sqd = ctx->sq_data;
                if (sqd) {
                        /*
                         * Observe the correct sqd->lock -> ctx->uring_lock
                         * ordering. Fine to drop uring_lock here, we hold
                         * a ref to the ctx.
                         */
                        refcount_inc(&sqd->refs);
                        mutex_unlock(&ctx->uring_lock);
                        mutex_lock(&sqd->lock);
                        mutex_lock(&ctx->uring_lock);
                        if (sqd->thread)
                                tctx = sqd->thread->io_uring;
                }
        } else {
                tctx = current->io_uring;
        }

        BUILD_BUG_ON(sizeof(new_count) != sizeof(ctx->iowq_limits));

        for (i = 0; i < ARRAY_SIZE(new_count); i++)
                if (new_count[i])
                        ctx->iowq_limits[i] = new_count[i];
        ctx->iowq_limits_set = true;

        if (tctx && tctx->io_wq) {
                ret = io_wq_max_workers(tctx->io_wq, new_count);
                if (ret)
                        goto err;
        } else {
                memset(new_count, 0, sizeof(new_count));
        }

        if (sqd) {
                mutex_unlock(&sqd->lock);
                io_put_sq_data(sqd);
        }

        if (copy_to_user(arg, new_count, sizeof(new_count)))
                return -EFAULT;

        /* that's it for SQPOLL, only the SQPOLL task creates requests */
        if (sqd)
                return 0;

        /* now propagate the restriction to all registered users */
        list_for_each_entry(node, &ctx->tctx_list, ctx_node) {
                struct io_uring_task *tctx = node->task->io_uring;

                if (WARN_ON_ONCE(!tctx->io_wq))
                        continue;

                for (i = 0; i < ARRAY_SIZE(new_count); i++)
                        new_count[i] = ctx->iowq_limits[i];
                /* ignore errors, it always returns zero anyway */
                (void)io_wq_max_workers(tctx->io_wq, new_count);
        }
        return 0;
err:
        if (sqd) {
                mutex_unlock(&sqd->lock);
                io_put_sq_data(sqd);
        }
        return ret;
}

static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
                               void __user *arg, unsigned nr_args)
        __releases(ctx->uring_lock)
        __acquires(ctx->uring_lock)
{
        int ret;

        /*
         * We don't quiesce the refs for register anymore and so it can't be
         * dying as we're holding a file ref here.
         */
        if (WARN_ON_ONCE(percpu_ref_is_dying(&ctx->refs)))
                return -ENXIO;

        if (ctx->submitter_task && ctx->submitter_task != current)
                return -EEXIST;

        if (ctx->restricted) {
                opcode = array_index_nospec(opcode, IORING_REGISTER_LAST);
                if (!test_bit(opcode, ctx->restrictions.register_op))
                        return -EACCES;
        }

        switch (opcode) {
        case IORING_REGISTER_BUFFERS:
                ret = -EFAULT;
                if (!arg)
                        break;
                ret = io_sqe_buffers_register(ctx, arg, nr_args, NULL);
                break;
        case IORING_UNREGISTER_BUFFERS:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_sqe_buffers_unregister(ctx);
                break;
        case IORING_REGISTER_FILES:
                ret = -EFAULT;
                if (!arg)
                        break;
                ret = io_sqe_files_register(ctx, arg, nr_args, NULL);
                break;
        case IORING_UNREGISTER_FILES:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_sqe_files_unregister(ctx);
                break;
        case IORING_REGISTER_FILES_UPDATE:
                ret = io_register_files_update(ctx, arg, nr_args);
                break;
        case IORING_REGISTER_EVENTFD:
                ret = -EINVAL;
                if (nr_args != 1)
                        break;
                ret = io_eventfd_register(ctx, arg, 0);
                break;
        case IORING_REGISTER_EVENTFD_ASYNC:
                ret = -EINVAL;
                if (nr_args != 1)
                        break;
                ret = io_eventfd_register(ctx, arg, 1);
                break;
        case IORING_UNREGISTER_EVENTFD:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_eventfd_unregister(ctx);
                break;
        case IORING_REGISTER_PROBE:
                ret = -EINVAL;
                if (!arg || nr_args > 256)
                        break;
                ret = io_probe(ctx, arg, nr_args);
                break;
        case IORING_REGISTER_PERSONALITY:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_register_personality(ctx);
                break;
        case IORING_UNREGISTER_PERSONALITY:
                ret = -EINVAL;
                if (arg)
                        break;
                ret = io_unregister_personality(ctx, nr_args);
                break;
        case IORING_REGISTER_ENABLE_RINGS:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_register_enable_rings(ctx);
                break;
        case IORING_REGISTER_RESTRICTIONS:
                ret = io_register_restrictions(ctx, arg, nr_args);
                break;
        case IORING_REGISTER_FILES2:
                ret = io_register_rsrc(ctx, arg, nr_args, IORING_RSRC_FILE);
                break;
        case IORING_REGISTER_FILES_UPDATE2:
                ret = io_register_rsrc_update(ctx, arg, nr_args,
                                              IORING_RSRC_FILE);
                break;
        case IORING_REGISTER_BUFFERS2:
                ret = io_register_rsrc(ctx, arg, nr_args, IORING_RSRC_BUFFER);
                break;
        case IORING_REGISTER_BUFFERS_UPDATE:
                ret = io_register_rsrc_update(ctx, arg, nr_args,
                                              IORING_RSRC_BUFFER);
                break;
        case IORING_REGISTER_IOWQ_AFF:
                ret = -EINVAL;
                if (!arg || !nr_args)
                        break;
                ret = io_register_iowq_aff(ctx, arg, nr_args);
                break;
        case IORING_UNREGISTER_IOWQ_AFF:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_unregister_iowq_aff(ctx);
                break;
        case IORING_REGISTER_IOWQ_MAX_WORKERS:
                ret = -EINVAL;
                if (!arg || nr_args != 2)
                        break;
                ret = io_register_iowq_max_workers(ctx, arg);
                break;
        case IORING_REGISTER_RING_FDS:
                ret = io_ringfd_register(ctx, arg, nr_args);
                break;
        case IORING_UNREGISTER_RING_FDS:
                ret = io_ringfd_unregister(ctx, arg, nr_args);
                break;
        case IORING_REGISTER_PBUF_RING:
                ret = -EINVAL;
                if (!arg || nr_args != 1)
                        break;
                ret = io_register_pbuf_ring(ctx, arg);
                break;
        case IORING_UNREGISTER_PBUF_RING:
                ret = -EINVAL;
                if (!arg || nr_args != 1)
                        break;
                ret = io_unregister_pbuf_ring(ctx, arg);
                break;
        case IORING_REGISTER_SYNC_CANCEL:
                ret = -EINVAL;
                if (!arg || nr_args != 1)
                        break;
                ret = io_sync_cancel(ctx, arg);
                break;
        case IORING_REGISTER_FILE_ALLOC_RANGE:
                ret = -EINVAL;
                if (!arg || nr_args)
                        break;
                ret = io_register_file_alloc_range(ctx, arg);
                break;
        default:
                ret = -EINVAL;
                break;
        }

        return ret;
}

SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
                void __user *, arg, unsigned int, nr_args)
{
        struct io_ring_ctx *ctx;
        long ret = -EBADF;
        struct fd f;
        bool use_registered_ring;

        use_registered_ring = !!(opcode & IORING_REGISTER_USE_REGISTERED_RING);
        opcode &= ~IORING_REGISTER_USE_REGISTERED_RING;

        if (opcode >= IORING_REGISTER_LAST)
                return -EINVAL;

        if (use_registered_ring) {
                /*
                 * Ring fd has been registered via IORING_REGISTER_RING_FDS, we
                 * need only dereference our task private array to find it.
                 */
                struct io_uring_task *tctx = current->io_uring;

                if (unlikely(!tctx || fd >= IO_RINGFD_REG_MAX))
                        return -EINVAL;
                fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
                f.file = tctx->registered_rings[fd];
                f.flags = 0;
                if (unlikely(!f.file))
                        return -EBADF;
        } else {
                f = fdget(fd);
                if (unlikely(!f.file))
                        return -EBADF;
                ret = -EOPNOTSUPP;
                if (!io_is_uring_fops(f.file))
                        goto out_fput;
        }

        ctx = f.file->private_data;

        mutex_lock(&ctx->uring_lock);
        ret = __io_uring_register(ctx, opcode, arg, nr_args);
        mutex_unlock(&ctx->uring_lock);
        trace_io_uring_register(ctx, opcode, ctx->nr_user_files, ctx->nr_user_bufs, ret);
out_fput:
        fdput(f);
        return ret;
}

static int __init io_uring_init(void)
{
#define __BUILD_BUG_VERIFY_OFFSET_SIZE(stype, eoffset, esize, ename) do { \
        BUILD_BUG_ON(offsetof(stype, ename) != eoffset); \
        BUILD_BUG_ON(sizeof_field(stype, ename) != esize); \
} while (0)

#define BUILD_BUG_SQE_ELEM(eoffset, etype, ename) \
        __BUILD_BUG_VERIFY_OFFSET_SIZE(struct io_uring_sqe, eoffset, sizeof(etype), ename)
#define BUILD_BUG_SQE_ELEM_SIZE(eoffset, esize, ename) \
        __BUILD_BUG_VERIFY_OFFSET_SIZE(struct io_uring_sqe, eoffset, esize, ename)
        BUILD_BUG_ON(sizeof(struct io_uring_sqe) != 64);
        BUILD_BUG_SQE_ELEM(0,  __u8,   opcode);
        BUILD_BUG_SQE_ELEM(1,  __u8,   flags);
        BUILD_BUG_SQE_ELEM(2,  __u16,  ioprio);
        BUILD_BUG_SQE_ELEM(4,  __s32,  fd);
        BUILD_BUG_SQE_ELEM(8,  __u64,  off);
        BUILD_BUG_SQE_ELEM(8,  __u64,  addr2);
        BUILD_BUG_SQE_ELEM(8,  __u32,  cmd_op);
        BUILD_BUG_SQE_ELEM(12, __u32, __pad1);
        BUILD_BUG_SQE_ELEM(16, __u64,  addr);
        BUILD_BUG_SQE_ELEM(16, __u64,  splice_off_in);
        BUILD_BUG_SQE_ELEM(24, __u32,  len);
        BUILD_BUG_SQE_ELEM(28,     __kernel_rwf_t, rw_flags);
        BUILD_BUG_SQE_ELEM(28, /* compat */   int, rw_flags);
        BUILD_BUG_SQE_ELEM(28, /* compat */ __u32, rw_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  fsync_flags);
        BUILD_BUG_SQE_ELEM(28, /* compat */ __u16,  poll_events);
        BUILD_BUG_SQE_ELEM(28, __u32,  poll32_events);
        BUILD_BUG_SQE_ELEM(28, __u32,  sync_range_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  msg_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  timeout_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  accept_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  cancel_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  open_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  statx_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  fadvise_advice);
        BUILD_BUG_SQE_ELEM(28, __u32,  splice_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  rename_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  unlink_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  hardlink_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  xattr_flags);
        BUILD_BUG_SQE_ELEM(28, __u32,  msg_ring_flags);
        BUILD_BUG_SQE_ELEM(32, __u64,  user_data);
        BUILD_BUG_SQE_ELEM(40, __u16,  buf_index);
        BUILD_BUG_SQE_ELEM(40, __u16,  buf_group);
        BUILD_BUG_SQE_ELEM(42, __u16,  personality);
        BUILD_BUG_SQE_ELEM(44, __s32,  splice_fd_in);
        BUILD_BUG_SQE_ELEM(44, __u32,  file_index);
        BUILD_BUG_SQE_ELEM(44, __u16,  addr_len);
        BUILD_BUG_SQE_ELEM(46, __u16,  __pad3[0]);
        BUILD_BUG_SQE_ELEM(48, __u64,  addr3);
        BUILD_BUG_SQE_ELEM_SIZE(48, 0, cmd);
        BUILD_BUG_SQE_ELEM(56, __u64,  __pad2);

        BUILD_BUG_ON(sizeof(struct io_uring_files_update) !=
                     sizeof(struct io_uring_rsrc_update));
        BUILD_BUG_ON(sizeof(struct io_uring_rsrc_update) >
                     sizeof(struct io_uring_rsrc_update2));

        /* ->buf_index is u16 */
        BUILD_BUG_ON(offsetof(struct io_uring_buf_ring, bufs) != 0);
        BUILD_BUG_ON(offsetof(struct io_uring_buf, resv) !=
                     offsetof(struct io_uring_buf_ring, tail));

        /* should fit into one byte */
        BUILD_BUG_ON(SQE_VALID_FLAGS >= (1 << 8));
        BUILD_BUG_ON(SQE_COMMON_FLAGS >= (1 << 8));
        BUILD_BUG_ON((SQE_VALID_FLAGS | SQE_COMMON_FLAGS) != SQE_VALID_FLAGS);

        BUILD_BUG_ON(__REQ_F_LAST_BIT > 8 * sizeof(int));

        BUILD_BUG_ON(sizeof(atomic_t) != sizeof(u32));

        io_uring_optable_init();

        req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC |
                                SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
        return 0;
};
__initcall(io_uring_init);