io_uring: don't enter poll loop if we have CQEs pending

[linux.git] / fs / 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_cqring (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 <linux/compat.h>
#include <linux/refcount.h>
#include <linux/uio.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/mmu_context.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include <linux/kthread.h>
#include <linux/blkdev.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/sizes.h>
#include <linux/hugetlb.h>

#include <uapi/linux/io_uring.h>

#include "internal.h"

#define IORING_MAX_ENTRIES      4096
#define IORING_MAX_FIXED_FILES  1024

struct io_uring {
        u32 head ____cacheline_aligned_in_smp;
        u32 tail ____cacheline_aligned_in_smp;
};

/*
 * This data is shared with the application through the mmap at offset
 * IORING_OFF_SQ_RING.
 *
 * The offsets to the member fields are published through struct
 * io_sqring_offsets when calling io_uring_setup.
 */
struct io_sq_ring {
        /*
         * Head and tail offsets into the ring; the offsets need to be
         * masked to get valid indices.
         *
         * The kernel controls head and the application controls tail.
         */
        struct io_uring         r;
        /*
         * Bitmask to apply to head and tail offsets (constant, equals
         * ring_entries - 1)
         */
        u32                     ring_mask;
        /* Ring size (constant, power of 2) */
        u32                     ring_entries;
        /*
         * Number of invalid entries dropped by the kernel due to
         * invalid index stored in array
         *
         * Written by the kernel, shouldn't be modified by the
         * application (i.e. get number of "new events" by comparing to
         * cached value).
         *
         * After a new SQ head value was read by the application this
         * counter includes all submissions that were dropped reaching
         * the new SQ head (and possibly more).
         */
        u32                     dropped;
        /*
         * Runtime flags
         *
         * Written by the kernel, shouldn't be modified by the
         * application.
         *
         * The application needs a full memory barrier before checking
         * for IORING_SQ_NEED_WAKEUP after updating the sq tail.
         */
        u32                     flags;
        /*
         * Ring buffer of indices into array of io_uring_sqe, which is
         * mmapped by the application using the IORING_OFF_SQES offset.
         *
         * This indirection could e.g. be used to assign fixed
         * io_uring_sqe entries to operations and only submit them to
         * the queue when needed.
         *
         * The kernel modifies neither the indices array nor the entries
         * array.
         */
        u32                     array[];
};

/*
 * This data is shared with the application through the mmap at offset
 * IORING_OFF_CQ_RING.
 *
 * The offsets to the member fields are published through struct
 * io_cqring_offsets when calling io_uring_setup.
 */
struct io_cq_ring {
        /*
         * Head and tail offsets into the ring; the offsets need to be
         * masked to get valid indices.
         *
         * The application controls head and the kernel tail.
         */
        struct io_uring         r;
        /*
         * Bitmask to apply to head and tail offsets (constant, equals
         * ring_entries - 1)
         */
        u32                     ring_mask;
        /* Ring size (constant, power of 2) */
        u32                     ring_entries;
        /*
         * Number of completion events lost because the queue was full;
         * this should be avoided by the application by making sure
         * there are not more requests pending thatn there is space in
         * the completion queue.
         *
         * Written by the kernel, shouldn't be modified by the
         * application (i.e. get number of "new events" by comparing to
         * cached value).
         *
         * As completion events come in out of order this counter is not
         * ordered with any other data.
         */
        u32                     overflow;
        /*
         * Ring buffer of completion events.
         *
         * The kernel writes completion events fresh every time they are
         * produced, so the application is allowed to modify pending
         * entries.
         */
        struct io_uring_cqe     cqes[];
};

struct io_mapped_ubuf {
        u64             ubuf;
        size_t          len;
        struct          bio_vec *bvec;
        unsigned int    nr_bvecs;
};

struct async_list {
        spinlock_t              lock;
        atomic_t                cnt;
        struct list_head        list;

        struct file             *file;
        off_t                   io_end;
        size_t                  io_len;
};

struct io_ring_ctx {
        struct {
                struct percpu_ref       refs;
        } ____cacheline_aligned_in_smp;

        struct {
                unsigned int            flags;
                bool                    compat;
                bool                    account_mem;

                /* SQ ring */
                struct io_sq_ring       *sq_ring;
                unsigned                cached_sq_head;
                unsigned                sq_entries;
                unsigned                sq_mask;
                unsigned                sq_thread_idle;
                struct io_uring_sqe     *sq_sqes;

                struct list_head        defer_list;
        } ____cacheline_aligned_in_smp;

        /* IO offload */
        struct workqueue_struct *sqo_wq;
        struct task_struct      *sqo_thread;    /* if using sq thread polling */
        struct mm_struct        *sqo_mm;
        wait_queue_head_t       sqo_wait;
        struct completion       sqo_thread_started;

        struct {
                /* CQ ring */
                struct io_cq_ring       *cq_ring;
                unsigned                cached_cq_tail;
                unsigned                cq_entries;
                unsigned                cq_mask;
                struct wait_queue_head  cq_wait;
                struct fasync_struct    *cq_fasync;
                struct eventfd_ctx      *cq_ev_fd;
        } ____cacheline_aligned_in_smp;

        /*
         * If used, fixed file set. Writers must ensure that ->refs is dead,
         * readers must ensure that ->refs is alive as long as the file* is
         * used. Only updated through io_uring_register(2).
         */
        struct file             **user_files;
        unsigned                nr_user_files;

        /* if used, fixed mapped user buffers */
        unsigned                nr_user_bufs;
        struct io_mapped_ubuf   *user_bufs;

        struct user_struct      *user;

        struct completion       ctx_done;

        struct {
                struct mutex            uring_lock;
                wait_queue_head_t       wait;
        } ____cacheline_aligned_in_smp;

        struct {
                spinlock_t              completion_lock;
                bool                    poll_multi_file;
                /*
                 * ->poll_list is protected by the ctx->uring_lock for
                 * io_uring instances that don't use IORING_SETUP_SQPOLL.
                 * For SQPOLL, only the single threaded io_sq_thread() will
                 * manipulate the list, hence no extra locking is needed there.
                 */
                struct list_head        poll_list;
                struct list_head        cancel_list;
        } ____cacheline_aligned_in_smp;

        struct async_list       pending_async[2];

#if defined(CONFIG_UNIX)
        struct socket           *ring_sock;
#endif
};

struct sqe_submit {
        const struct io_uring_sqe       *sqe;
        unsigned short                  index;
        bool                            has_user;
        bool                            needs_lock;
        bool                            needs_fixed_file;
};

/*
 * First field must be the file pointer in all the
 * iocb unions! See also 'struct kiocb' in <linux/fs.h>
 */
struct io_poll_iocb {
        struct file                     *file;
        struct wait_queue_head          *head;
        __poll_t                        events;
        bool                            done;
        bool                            canceled;
        struct wait_queue_entry         wait;
};

/*
 * NOTE! Each of the iocb union members has the file pointer
 * as the first entry in their struct definition. So you can
 * access the file pointer through any of the sub-structs,
 * or directly as just 'ki_filp' in this struct.
 */
struct io_kiocb {
        union {
                struct file             *file;
                struct kiocb            rw;
                struct io_poll_iocb     poll;
        };

        struct sqe_submit       submit;

        struct io_ring_ctx      *ctx;
        struct list_head        list;
        struct list_head        link_list;
        unsigned int            flags;
        refcount_t              refs;
#define REQ_F_NOWAIT            1       /* must not punt to workers */
#define REQ_F_IOPOLL_COMPLETED  2       /* polled IO has completed */
#define REQ_F_FIXED_FILE        4       /* ctx owns file */
#define REQ_F_SEQ_PREV          8       /* sequential with previous */
#define REQ_F_IO_DRAIN          16      /* drain existing IO first */
#define REQ_F_IO_DRAINED        32      /* drain done */
#define REQ_F_LINK              64      /* linked sqes */
#define REQ_F_LINK_DONE         128     /* linked sqes done */
#define REQ_F_FAIL_LINK         256     /* fail rest of links */
        u64                     user_data;
        u32                     result;
        u32                     sequence;

        struct work_struct      work;
};

#define IO_PLUG_THRESHOLD               2
#define IO_IOPOLL_BATCH                 8

struct io_submit_state {
        struct blk_plug         plug;

        /*
         * io_kiocb alloc cache
         */
        void                    *reqs[IO_IOPOLL_BATCH];
        unsigned                int free_reqs;
        unsigned                int cur_req;

        /*
         * File reference cache
         */
        struct file             *file;
        unsigned int            fd;
        unsigned int            has_refs;
        unsigned int            used_refs;
        unsigned int            ios_left;
};

static void io_sq_wq_submit_work(struct work_struct *work);

static struct kmem_cache *req_cachep;

static const struct file_operations io_uring_fops;

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

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

static 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->ctx_done);
}

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

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

        if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free,
                            PERCPU_REF_ALLOW_REINIT, GFP_KERNEL)) {
                kfree(ctx);
                return NULL;
        }

        ctx->flags = p->flags;
        init_waitqueue_head(&ctx->cq_wait);
        init_completion(&ctx->ctx_done);
        init_completion(&ctx->sqo_thread_started);
        mutex_init(&ctx->uring_lock);
        init_waitqueue_head(&ctx->wait);
        for (i = 0; i < ARRAY_SIZE(ctx->pending_async); i++) {
                spin_lock_init(&ctx->pending_async[i].lock);
                INIT_LIST_HEAD(&ctx->pending_async[i].list);
                atomic_set(&ctx->pending_async[i].cnt, 0);
        }
        spin_lock_init(&ctx->completion_lock);
        INIT_LIST_HEAD(&ctx->poll_list);
        INIT_LIST_HEAD(&ctx->cancel_list);
        INIT_LIST_HEAD(&ctx->defer_list);
        return ctx;
}

static inline bool io_sequence_defer(struct io_ring_ctx *ctx,
                                     struct io_kiocb *req)
{
        if ((req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) != REQ_F_IO_DRAIN)
                return false;

        return req->sequence != ctx->cached_cq_tail + ctx->sq_ring->dropped;
}

static struct io_kiocb *io_get_deferred_req(struct io_ring_ctx *ctx)
{
        struct io_kiocb *req;

        if (list_empty(&ctx->defer_list))
                return NULL;

        req = list_first_entry(&ctx->defer_list, struct io_kiocb, list);
        if (!io_sequence_defer(ctx, req)) {
                list_del_init(&req->list);
                return req;
        }

        return NULL;
}

static void __io_commit_cqring(struct io_ring_ctx *ctx)
{
        struct io_cq_ring *ring = ctx->cq_ring;

        if (ctx->cached_cq_tail != READ_ONCE(ring->r.tail)) {
                /* order cqe stores with ring update */
                smp_store_release(&ring->r.tail, ctx->cached_cq_tail);

                if (wq_has_sleeper(&ctx->cq_wait)) {
                        wake_up_interruptible(&ctx->cq_wait);
                        kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
                }
        }
}

static void io_commit_cqring(struct io_ring_ctx *ctx)
{
        struct io_kiocb *req;

        __io_commit_cqring(ctx);

        while ((req = io_get_deferred_req(ctx)) != NULL) {
                req->flags |= REQ_F_IO_DRAINED;
                queue_work(ctx->sqo_wq, &req->work);
        }
}

static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx)
{
        struct io_cq_ring *ring = ctx->cq_ring;
        unsigned tail;

        tail = ctx->cached_cq_tail;
        /*
         * 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
         */
        if (tail - READ_ONCE(ring->r.head) == ring->ring_entries)
                return NULL;

        ctx->cached_cq_tail++;
        return &ring->cqes[tail & ctx->cq_mask];
}

static void io_cqring_fill_event(struct io_ring_ctx *ctx, u64 ki_user_data,
                                 long res)
{
        struct io_uring_cqe *cqe;

        /*
         * 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_cqring(ctx);
        if (cqe) {
                WRITE_ONCE(cqe->user_data, ki_user_data);
                WRITE_ONCE(cqe->res, res);
                WRITE_ONCE(cqe->flags, 0);
        } else {
                unsigned overflow = READ_ONCE(ctx->cq_ring->overflow);

                WRITE_ONCE(ctx->cq_ring->overflow, overflow + 1);
        }
}

static void io_cqring_ev_posted(struct io_ring_ctx *ctx)
{
        if (waitqueue_active(&ctx->wait))
                wake_up(&ctx->wait);
        if (waitqueue_active(&ctx->sqo_wait))
                wake_up(&ctx->sqo_wait);
        if (ctx->cq_ev_fd)
                eventfd_signal(ctx->cq_ev_fd, 1);
}

static void io_cqring_add_event(struct io_ring_ctx *ctx, u64 user_data,
                                long res)
{
        unsigned long flags;

        spin_lock_irqsave(&ctx->completion_lock, flags);
        io_cqring_fill_event(ctx, user_data, res);
        io_commit_cqring(ctx);
        spin_unlock_irqrestore(&ctx->completion_lock, flags);

        io_cqring_ev_posted(ctx);
}

static void io_ring_drop_ctx_refs(struct io_ring_ctx *ctx, unsigned refs)
{
        percpu_ref_put_many(&ctx->refs, refs);

        if (waitqueue_active(&ctx->wait))
                wake_up(&ctx->wait);
}

static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
                                   struct io_submit_state *state)
{
        gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
        struct io_kiocb *req;

        if (!percpu_ref_tryget(&ctx->refs))
                return NULL;

        if (!state) {
                req = kmem_cache_alloc(req_cachep, gfp);
                if (unlikely(!req))
                        goto out;
        } else if (!state->free_reqs) {
                size_t sz;
                int ret;

                sz = min_t(size_t, state->ios_left, ARRAY_SIZE(state->reqs));
                ret = kmem_cache_alloc_bulk(req_cachep, gfp, sz, state->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)) {
                        state->reqs[0] = kmem_cache_alloc(req_cachep, gfp);
                        if (!state->reqs[0])
                                goto out;
                        ret = 1;
                }
                state->free_reqs = ret - 1;
                state->cur_req = 1;
                req = state->reqs[0];
        } else {
                req = state->reqs[state->cur_req];
                state->free_reqs--;
                state->cur_req++;
        }

        req->file = NULL;
        req->ctx = ctx;
        req->flags = 0;
        /* one is dropped after submission, the other at completion */
        refcount_set(&req->refs, 2);
        req->result = 0;
        return req;
out:
        io_ring_drop_ctx_refs(ctx, 1);
        return NULL;
}

static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
{
        if (*nr) {
                kmem_cache_free_bulk(req_cachep, *nr, reqs);
                io_ring_drop_ctx_refs(ctx, *nr);
                *nr = 0;
        }
}

static void __io_free_req(struct io_kiocb *req)
{
        if (req->file && !(req->flags & REQ_F_FIXED_FILE))
                fput(req->file);
        io_ring_drop_ctx_refs(req->ctx, 1);
        kmem_cache_free(req_cachep, req);
}

static void io_req_link_next(struct io_kiocb *req)
{
        struct io_kiocb *nxt;

        /*
         * The list should never be empty when we are called here. But could
         * potentially happen if the chain is messed up, check to be on the
         * safe side.
         */
        nxt = list_first_entry_or_null(&req->link_list, struct io_kiocb, list);
        if (nxt) {
                list_del(&nxt->list);
                if (!list_empty(&req->link_list)) {
                        INIT_LIST_HEAD(&nxt->link_list);
                        list_splice(&req->link_list, &nxt->link_list);
                        nxt->flags |= REQ_F_LINK;
                }

                nxt->flags |= REQ_F_LINK_DONE;
                INIT_WORK(&nxt->work, io_sq_wq_submit_work);
                queue_work(req->ctx->sqo_wq, &nxt->work);
        }
}

/*
 * Called if REQ_F_LINK is set, and we fail the head request
 */
static void io_fail_links(struct io_kiocb *req)
{
        struct io_kiocb *link;

        while (!list_empty(&req->link_list)) {
                link = list_first_entry(&req->link_list, struct io_kiocb, list);
                list_del(&link->list);

                io_cqring_add_event(req->ctx, link->user_data, -ECANCELED);
                __io_free_req(link);
        }
}

static void io_free_req(struct io_kiocb *req)
{
        /*
         * 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 (req->flags & REQ_F_LINK) {
                if (req->flags & REQ_F_FAIL_LINK)
                        io_fail_links(req);
                else
                        io_req_link_next(req);
        }

        __io_free_req(req);
}

static void io_put_req(struct io_kiocb *req)
{
        if (refcount_dec_and_test(&req->refs))
                io_free_req(req);
}

static unsigned io_cqring_events(struct io_cq_ring *ring)
{
        /* See comment at the top of this file */
        smp_rmb();
        return READ_ONCE(ring->r.tail) - READ_ONCE(ring->r.head);
}

/*
 * Find and free completed poll iocbs
 */
static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
                               struct list_head *done)
{
        void *reqs[IO_IOPOLL_BATCH];
        struct io_kiocb *req;
        int to_free;

        to_free = 0;
        while (!list_empty(done)) {
                req = list_first_entry(done, struct io_kiocb, list);
                list_del(&req->list);

                io_cqring_fill_event(ctx, req->user_data, req->result);
                (*nr_events)++;

                if (refcount_dec_and_test(&req->refs)) {
                        /* If we're not using fixed files, we have to pair the
                         * completion part with the file put. Use regular
                         * completions for those, only batch free for fixed
                         * file and non-linked commands.
                         */
                        if ((req->flags & (REQ_F_FIXED_FILE|REQ_F_LINK)) ==
                            REQ_F_FIXED_FILE) {
                                reqs[to_free++] = req;
                                if (to_free == ARRAY_SIZE(reqs))
                                        io_free_req_many(ctx, reqs, &to_free);
                        } else {
                                io_free_req(req);
                        }
                }
        }

        io_commit_cqring(ctx);
        io_free_req_many(ctx, reqs, &to_free);
}

static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
                        long min)
{
        struct io_kiocb *req, *tmp;
        LIST_HEAD(done);
        bool spin;
        int ret;

        /*
         * Only spin for completions if we don't have multiple devices hanging
         * off our complete list, and we're under the requested amount.
         */
        spin = !ctx->poll_multi_file && *nr_events < min;

        ret = 0;
        list_for_each_entry_safe(req, tmp, &ctx->poll_list, list) {
                struct kiocb *kiocb = &req->rw;

                /*
                 * Move completed entries to our local list. If we find a
                 * request that requires polling, break out and complete
                 * the done list first, if we have entries there.
                 */
                if (req->flags & REQ_F_IOPOLL_COMPLETED) {
                        list_move_tail(&req->list, &done);
                        continue;
                }
                if (!list_empty(&done))
                        break;

                ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
                if (ret < 0)
                        break;

                if (ret && spin)
                        spin = false;
                ret = 0;
        }

        if (!list_empty(&done))
                io_iopoll_complete(ctx, nr_events, &done);

        return ret;
}

/*
 * Poll for a mininum of 'min' events. Note that if min == 0 we consider that a
 * non-spinning poll check - we'll still enter the driver poll loop, but only
 * as a non-spinning completion check.
 */
static int io_iopoll_getevents(struct io_ring_ctx *ctx, unsigned int *nr_events,
                                long min)
{
        while (!list_empty(&ctx->poll_list)) {
                int ret;

                ret = io_do_iopoll(ctx, nr_events, min);
                if (ret < 0)
                        return ret;
                if (!min || *nr_events >= min)
                        return 0;
        }

        return 1;
}

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

        mutex_lock(&ctx->uring_lock);
        while (!list_empty(&ctx->poll_list)) {
                unsigned int nr_events = 0;

                io_iopoll_getevents(ctx, &nr_events, 1);
        }
        mutex_unlock(&ctx->uring_lock);
}

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

        /*
         * 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);

        iters = 0;
        do {
                int tmin = 0;

                /*
                 * 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->cq_ring))
                        break;

                /*
                 * 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 (!(++iters & 7)) {
                        mutex_unlock(&ctx->uring_lock);
                        mutex_lock(&ctx->uring_lock);
                }

                if (*nr_events < min)
                        tmin = min - *nr_events;

                ret = io_iopoll_getevents(ctx, nr_events, tmin);
                if (ret <= 0)
                        break;
                ret = 0;
        } while (min && !*nr_events && !need_resched());

        mutex_unlock(&ctx->uring_lock);
        return ret;
}

static void kiocb_end_write(struct kiocb *kiocb)
{
        if (kiocb->ki_flags & IOCB_WRITE) {
                struct inode *inode = file_inode(kiocb->ki_filp);

                /*
                 * Tell lockdep we inherited freeze protection from submission
                 * thread.
                 */
                if (S_ISREG(inode->i_mode))
                        __sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
                file_end_write(kiocb->ki_filp);
        }
}

static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
{
        struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);

        kiocb_end_write(kiocb);

        if ((req->flags & REQ_F_LINK) && res != req->result)
                req->flags |= REQ_F_FAIL_LINK;
        io_cqring_add_event(req->ctx, req->user_data, res);
        io_put_req(req);
}

static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
{
        struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);

        kiocb_end_write(kiocb);

        if ((req->flags & REQ_F_LINK) && res != req->result)
                req->flags |= REQ_F_FAIL_LINK;
        req->result = res;
        if (res != -EAGAIN)
                req->flags |= REQ_F_IOPOLL_COMPLETED;
}

/*
 * 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_iopoll_getevents() thread before the issuer is done
 * accessing the kiocb cookie.
 */
static void io_iopoll_req_issued(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;

        /*
         * 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 (list_empty(&ctx->poll_list)) {
                ctx->poll_multi_file = false;
        } else if (!ctx->poll_multi_file) {
                struct io_kiocb *list_req;

                list_req = list_first_entry(&ctx->poll_list, struct io_kiocb,
                                                list);
                if (list_req->rw.ki_filp != req->rw.ki_filp)
                        ctx->poll_multi_file = true;
        }

        /*
         * For fast devices, IO may have already completed. If it has, add
         * it to the front so we find it first.
         */
        if (req->flags & REQ_F_IOPOLL_COMPLETED)
                list_add(&req->list, &ctx->poll_list);
        else
                list_add_tail(&req->list, &ctx->poll_list);
}

static void io_file_put(struct io_submit_state *state)
{
        if (state->file) {
                int diff = state->has_refs - state->used_refs;

                if (diff)
                        fput_many(state->file, diff);
                state->file = NULL;
        }
}

/*
 * Get as many references to a file as we have IOs left in this submission,
 * assuming most submissions are for one file, or at least that each file
 * has more than one submission.
 */
static struct file *io_file_get(struct io_submit_state *state, int fd)
{
        if (!state)
                return fget(fd);

        if (state->file) {
                if (state->fd == fd) {
                        state->used_refs++;
                        state->ios_left--;
                        return state->file;
                }
                io_file_put(state);
        }
        state->file = fget_many(fd, state->ios_left);
        if (!state->file)
                return NULL;

        state->fd = fd;
        state->has_refs = state->ios_left;
        state->used_refs = 1;
        state->ios_left--;
        return state->file;
}

/*
 * 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_async(struct file *file)
{
        umode_t mode = file_inode(file)->i_mode;

        if (S_ISBLK(mode) || S_ISCHR(mode))
                return true;
        if (S_ISREG(mode) && file->f_op != &io_uring_fops)
                return true;

        return false;
}

static int io_prep_rw(struct io_kiocb *req, const struct sqe_submit *s,
                      bool force_nonblock)
{
        const struct io_uring_sqe *sqe = s->sqe;
        struct io_ring_ctx *ctx = req->ctx;
        struct kiocb *kiocb = &req->rw;
        unsigned ioprio;
        int ret;

        if (!req->file)
                return -EBADF;

        if (force_nonblock && !io_file_supports_async(req->file))
                force_nonblock = false;

        kiocb->ki_pos = READ_ONCE(sqe->off);
        kiocb->ki_flags = iocb_flags(kiocb->ki_filp);
        kiocb->ki_hint = ki_hint_validate(file_write_hint(kiocb->ki_filp));

        ioprio = READ_ONCE(sqe->ioprio);
        if (ioprio) {
                ret = ioprio_check_cap(ioprio);
                if (ret)
                        return ret;

                kiocb->ki_ioprio = ioprio;
        } else
                kiocb->ki_ioprio = get_current_ioprio();

        ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
        if (unlikely(ret))
                return ret;

        /* don't allow async punt if RWF_NOWAIT was requested */
        if (kiocb->ki_flags & IOCB_NOWAIT)
                req->flags |= REQ_F_NOWAIT;

        if (force_nonblock)
                kiocb->ki_flags |= IOCB_NOWAIT;

        if (ctx->flags & IORING_SETUP_IOPOLL) {
                if (!(kiocb->ki_flags & IOCB_DIRECT) ||
                    !kiocb->ki_filp->f_op->iopoll)
                        return -EOPNOTSUPP;

                kiocb->ki_flags |= IOCB_HIPRI;
                kiocb->ki_complete = io_complete_rw_iopoll;
        } else {
                if (kiocb->ki_flags & IOCB_HIPRI)
                        return -EINVAL;
                kiocb->ki_complete = io_complete_rw;
        }
        return 0;
}

static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
{
        switch (ret) {
        case -EIOCBQUEUED:
                break;
        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTARTNOHAND:
        case -ERESTART_RESTARTBLOCK:
                /*
                 * We can't just restart the syscall, since previously
                 * submitted sqes may already be in progress. Just fail this
                 * IO with EINTR.
                 */
                ret = -EINTR;
                /* fall through */
        default:
                kiocb->ki_complete(kiocb, ret, 0);
        }
}

static int io_import_fixed(struct io_ring_ctx *ctx, int rw,
                           const struct io_uring_sqe *sqe,
                           struct iov_iter *iter)
{
        size_t len = READ_ONCE(sqe->len);
        struct io_mapped_ubuf *imu;
        unsigned index, buf_index;
        size_t offset;
        u64 buf_addr;

        /* attempt to use fixed buffers without having provided iovecs */
        if (unlikely(!ctx->user_bufs))
                return -EFAULT;

        buf_index = READ_ONCE(sqe->buf_index);
        if (unlikely(buf_index >= ctx->nr_user_bufs))
                return -EFAULT;

        index = array_index_nospec(buf_index, ctx->nr_user_bufs);
        imu = &ctx->user_bufs[index];
        buf_addr = READ_ONCE(sqe->addr);

        /* overflow */
        if (buf_addr + len < buf_addr)
                return -EFAULT;
        /* not inside the mapped region */
        if (buf_addr < imu->ubuf || buf_addr + len > imu->ubuf + imu->len)
                return -EFAULT;

        /*
         * May not be a start of buffer, set size appropriately
         * and advance us to the beginning.
         */
        offset = buf_addr - imu->ubuf;
        iov_iter_bvec(iter, rw, imu->bvec, imu->nr_bvecs, offset + len);

        if (offset) {
                /*
                 * Don't use iov_iter_advance() here, as it's really slow for
                 * using the latter parts of a big fixed buffer - it iterates
                 * over each segment manually. We can cheat a bit here, because
                 * we know that:
                 *
                 * 1) it's a BVEC iter, we set it up
                 * 2) all bvecs are PAGE_SIZE in size, except potentially the
                 *    first and last bvec
                 *
                 * So just find our index, and adjust the iterator afterwards.
                 * If the offset is within the first bvec (or the whole first
                 * bvec, just use iov_iter_advance(). This makes it easier
                 * since we can just skip the first segment, which may not
                 * be PAGE_SIZE aligned.
                 */
                const struct bio_vec *bvec = imu->bvec;

                if (offset <= bvec->bv_len) {
                        iov_iter_advance(iter, offset);
                } else {
                        unsigned long seg_skip;

                        /* skip first vec */
                        offset -= bvec->bv_len;
                        seg_skip = 1 + (offset >> PAGE_SHIFT);

                        iter->bvec = bvec + seg_skip;
                        iter->nr_segs -= seg_skip;
                        iter->count -= bvec->bv_len + offset;
                        iter->iov_offset = offset & ~PAGE_MASK;
                }
        }

        return 0;
}

static ssize_t io_import_iovec(struct io_ring_ctx *ctx, int rw,
                               const struct sqe_submit *s, struct iovec **iovec,
                               struct iov_iter *iter)
{
        const struct io_uring_sqe *sqe = s->sqe;
        void __user *buf = u64_to_user_ptr(READ_ONCE(sqe->addr));
        size_t sqe_len = READ_ONCE(sqe->len);
        u8 opcode;

        /*
         * We're reading ->opcode for the second time, but the first read
         * doesn't care whether it's _FIXED or not, so it doesn't matter
         * whether ->opcode changes concurrently. The first read does care
         * about whether it is a READ or a WRITE, so we don't trust this read
         * for that purpose and instead let the caller pass in the read/write
         * flag.
         */
        opcode = READ_ONCE(sqe->opcode);
        if (opcode == IORING_OP_READ_FIXED ||
            opcode == IORING_OP_WRITE_FIXED) {
                ssize_t ret = io_import_fixed(ctx, rw, sqe, iter);
                *iovec = NULL;
                return ret;
        }

        if (!s->has_user)
                return -EFAULT;

#ifdef CONFIG_COMPAT
        if (ctx->compat)
                return compat_import_iovec(rw, buf, sqe_len, UIO_FASTIOV,
                                                iovec, iter);
#endif

        return import_iovec(rw, buf, sqe_len, UIO_FASTIOV, iovec, iter);
}

/*
 * Make a note of the last file/offset/direction we punted to async
 * context. We'll use this information to see if we can piggy back a
 * sequential request onto the previous one, if it's still hasn't been
 * completed by the async worker.
 */
static void io_async_list_note(int rw, struct io_kiocb *req, size_t len)
{
        struct async_list *async_list = &req->ctx->pending_async[rw];
        struct kiocb *kiocb = &req->rw;
        struct file *filp = kiocb->ki_filp;
        off_t io_end = kiocb->ki_pos + len;

        if (filp == async_list->file && kiocb->ki_pos == async_list->io_end) {
                unsigned long max_bytes;

                /* Use 8x RA size as a decent limiter for both reads/writes */
                max_bytes = filp->f_ra.ra_pages << (PAGE_SHIFT + 3);
                if (!max_bytes)
                        max_bytes = VM_READAHEAD_PAGES << (PAGE_SHIFT + 3);

                /* If max len are exceeded, reset the state */
                if (async_list->io_len + len <= max_bytes) {
                        req->flags |= REQ_F_SEQ_PREV;
                        async_list->io_len += len;
                } else {
                        io_end = 0;
                        async_list->io_len = 0;
                }
        }

        /* New file? Reset state. */
        if (async_list->file != filp) {
                async_list->io_len = 0;
                async_list->file = filp;
        }
        async_list->io_end = io_end;
}

static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
                   bool force_nonblock)
{
        struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
        struct kiocb *kiocb = &req->rw;
        struct iov_iter iter;
        struct file *file;
        size_t iov_count;
        ssize_t read_size, ret;

        ret = io_prep_rw(req, s, force_nonblock);
        if (ret)
                return ret;
        file = kiocb->ki_filp;

        if (unlikely(!(file->f_mode & FMODE_READ)))
                return -EBADF;
        if (unlikely(!file->f_op->read_iter))
                return -EINVAL;

        ret = io_import_iovec(req->ctx, READ, s, &iovec, &iter);
        if (ret < 0)
                return ret;

        read_size = ret;
        if (req->flags & REQ_F_LINK)
                req->result = read_size;

        iov_count = iov_iter_count(&iter);
        ret = rw_verify_area(READ, file, &kiocb->ki_pos, iov_count);
        if (!ret) {
                ssize_t ret2;

                ret2 = call_read_iter(file, kiocb, &iter);
                /*
                 * In case of a short read, punt to async. This can happen
                 * if we have data partially cached. Alternatively we can
                 * return the short read, in which case the application will
                 * need to issue another SQE and wait for it. That SQE will
                 * need async punt anyway, so it's more efficient to do it
                 * here.
                 */
                if (force_nonblock && ret2 > 0 && ret2 < read_size)
                        ret2 = -EAGAIN;
                /* Catch -EAGAIN return for forced non-blocking submission */
                if (!force_nonblock || ret2 != -EAGAIN) {
                        io_rw_done(kiocb, ret2);
                } else {
                        /*
                         * If ->needs_lock is true, we're already in async
                         * context.
                         */
                        if (!s->needs_lock)
                                io_async_list_note(READ, req, iov_count);
                        ret = -EAGAIN;
                }
        }
        kfree(iovec);
        return ret;
}

static int io_write(struct io_kiocb *req, const struct sqe_submit *s,
                    bool force_nonblock)
{
        struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
        struct kiocb *kiocb = &req->rw;
        struct iov_iter iter;
        struct file *file;
        size_t iov_count;
        ssize_t ret;

        ret = io_prep_rw(req, s, force_nonblock);
        if (ret)
                return ret;

        file = kiocb->ki_filp;
        if (unlikely(!(file->f_mode & FMODE_WRITE)))
                return -EBADF;
        if (unlikely(!file->f_op->write_iter))
                return -EINVAL;

        ret = io_import_iovec(req->ctx, WRITE, s, &iovec, &iter);
        if (ret < 0)
                return ret;

        if (req->flags & REQ_F_LINK)
                req->result = ret;

        iov_count = iov_iter_count(&iter);

        ret = -EAGAIN;
        if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT)) {
                /* If ->needs_lock is true, we're already in async context. */
                if (!s->needs_lock)
                        io_async_list_note(WRITE, req, iov_count);
                goto out_free;
        }

        ret = rw_verify_area(WRITE, file, &kiocb->ki_pos, iov_count);
        if (!ret) {
                ssize_t ret2;

                /*
                 * Open-code file_start_write here to grab freeze protection,
                 * which will be released by another thread in
                 * io_complete_rw().  Fool lockdep by telling it the lock got
                 * released so that it doesn't complain about the held lock when
                 * we return to userspace.
                 */
                if (S_ISREG(file_inode(file)->i_mode)) {
                        __sb_start_write(file_inode(file)->i_sb,
                                                SB_FREEZE_WRITE, true);
                        __sb_writers_release(file_inode(file)->i_sb,
                                                SB_FREEZE_WRITE);
                }
                kiocb->ki_flags |= IOCB_WRITE;

                ret2 = call_write_iter(file, kiocb, &iter);
                if (!force_nonblock || ret2 != -EAGAIN) {
                        io_rw_done(kiocb, ret2);
                } else {
                        /*
                         * If ->needs_lock is true, we're already in async
                         * context.
                         */
                        if (!s->needs_lock)
                                io_async_list_note(WRITE, req, iov_count);
                        ret = -EAGAIN;
                }
        }
out_free:
        kfree(iovec);
        return ret;
}

/*
 * IORING_OP_NOP just posts a completion event, nothing else.
 */
static int io_nop(struct io_kiocb *req, u64 user_data)
{
        struct io_ring_ctx *ctx = req->ctx;
        long err = 0;

        if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;

        io_cqring_add_event(ctx, user_data, err);
        io_put_req(req);
        return 0;
}

static int io_prep_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_ring_ctx *ctx = req->ctx;

        if (!req->file)
                return -EBADF;

        if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (unlikely(sqe->addr || sqe->ioprio || sqe->buf_index))
                return -EINVAL;

        return 0;
}

static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                    bool force_nonblock)
{
        loff_t sqe_off = READ_ONCE(sqe->off);
        loff_t sqe_len = READ_ONCE(sqe->len);
        loff_t end = sqe_off + sqe_len;
        unsigned fsync_flags;
        int ret;

        fsync_flags = READ_ONCE(sqe->fsync_flags);
        if (unlikely(fsync_flags & ~IORING_FSYNC_DATASYNC))
                return -EINVAL;

        ret = io_prep_fsync(req, sqe);
        if (ret)
                return ret;

        /* fsync always requires a blocking context */
        if (force_nonblock)
                return -EAGAIN;

        ret = vfs_fsync_range(req->rw.ki_filp, sqe_off,
                                end > 0 ? end : LLONG_MAX,
                                fsync_flags & IORING_FSYNC_DATASYNC);

        if (ret < 0 && (req->flags & REQ_F_LINK))
                req->flags |= REQ_F_FAIL_LINK;
        io_cqring_add_event(req->ctx, sqe->user_data, ret);
        io_put_req(req);
        return 0;
}

static int io_prep_sfr(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_ring_ctx *ctx = req->ctx;
        int ret = 0;

        if (!req->file)
                return -EBADF;

        if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (unlikely(sqe->addr || sqe->ioprio || sqe->buf_index))
                return -EINVAL;

        return ret;
}

static int io_sync_file_range(struct io_kiocb *req,
                              const struct io_uring_sqe *sqe,
                              bool force_nonblock)
{
        loff_t sqe_off;
        loff_t sqe_len;
        unsigned flags;
        int ret;

        ret = io_prep_sfr(req, sqe);
        if (ret)
                return ret;

        /* sync_file_range always requires a blocking context */
        if (force_nonblock)
                return -EAGAIN;

        sqe_off = READ_ONCE(sqe->off);
        sqe_len = READ_ONCE(sqe->len);
        flags = READ_ONCE(sqe->sync_range_flags);

        ret = sync_file_range(req->rw.ki_filp, sqe_off, sqe_len, flags);

        if (ret < 0 && (req->flags & REQ_F_LINK))
                req->flags |= REQ_F_FAIL_LINK;
        io_cqring_add_event(req->ctx, sqe->user_data, ret);
        io_put_req(req);
        return 0;
}

#if defined(CONFIG_NET)
static int io_send_recvmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                           bool force_nonblock,
                   long (*fn)(struct socket *, struct user_msghdr __user *,
                                unsigned int))
{
        struct socket *sock;
        int ret;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;

        sock = sock_from_file(req->file, &ret);
        if (sock) {
                struct user_msghdr __user *msg;
                unsigned flags;

                flags = READ_ONCE(sqe->msg_flags);
                if (flags & MSG_DONTWAIT)
                        req->flags |= REQ_F_NOWAIT;
                else if (force_nonblock)
                        flags |= MSG_DONTWAIT;

                msg = (struct user_msghdr __user *) (unsigned long)
                        READ_ONCE(sqe->addr);

                ret = fn(sock, msg, flags);
                if (force_nonblock && ret == -EAGAIN)
                        return ret;
        }

        io_cqring_add_event(req->ctx, sqe->user_data, ret);
        io_put_req(req);
        return 0;
}
#endif

static int io_sendmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                      bool force_nonblock)
{
#if defined(CONFIG_NET)
        return io_send_recvmsg(req, sqe, force_nonblock, __sys_sendmsg_sock);
#else
        return -EOPNOTSUPP;
#endif
}

static int io_recvmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                      bool force_nonblock)
{
#if defined(CONFIG_NET)
        return io_send_recvmsg(req, sqe, force_nonblock, __sys_recvmsg_sock);
#else
        return -EOPNOTSUPP;
#endif
}

static void io_poll_remove_one(struct io_kiocb *req)
{
        struct io_poll_iocb *poll = &req->poll;

        spin_lock(&poll->head->lock);
        WRITE_ONCE(poll->canceled, true);
        if (!list_empty(&poll->wait.entry)) {
                list_del_init(&poll->wait.entry);
                queue_work(req->ctx->sqo_wq, &req->work);
        }
        spin_unlock(&poll->head->lock);

        list_del_init(&req->list);
}

static void io_poll_remove_all(struct io_ring_ctx *ctx)
{
        struct io_kiocb *req;

        spin_lock_irq(&ctx->completion_lock);
        while (!list_empty(&ctx->cancel_list)) {
                req = list_first_entry(&ctx->cancel_list, struct io_kiocb,list);
                io_poll_remove_one(req);
        }
        spin_unlock_irq(&ctx->completion_lock);
}

/*
 * Find a running poll command that matches one specified in sqe->addr,
 * and remove it if found.
 */
static int io_poll_remove(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_kiocb *poll_req, *next;
        int ret = -ENOENT;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (sqe->ioprio || sqe->off || sqe->len || sqe->buf_index ||
            sqe->poll_events)
                return -EINVAL;

        spin_lock_irq(&ctx->completion_lock);
        list_for_each_entry_safe(poll_req, next, &ctx->cancel_list, list) {
                if (READ_ONCE(sqe->addr) == poll_req->user_data) {
                        io_poll_remove_one(poll_req);
                        ret = 0;
                        break;
                }
        }
        spin_unlock_irq(&ctx->completion_lock);

        io_cqring_add_event(req->ctx, sqe->user_data, ret);
        io_put_req(req);
        return 0;
}

static void io_poll_complete(struct io_ring_ctx *ctx, struct io_kiocb *req,
                             __poll_t mask)
{
        req->poll.done = true;
        io_cqring_fill_event(ctx, req->user_data, mangle_poll(mask));
        io_commit_cqring(ctx);
}

static void io_poll_complete_work(struct work_struct *work)
{
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);
        struct io_poll_iocb *poll = &req->poll;
        struct poll_table_struct pt = { ._key = poll->events };
        struct io_ring_ctx *ctx = req->ctx;
        __poll_t mask = 0;

        if (!READ_ONCE(poll->canceled))
                mask = vfs_poll(poll->file, &pt) & poll->events;

        /*
         * Note that ->ki_cancel callers also delete iocb from active_reqs after
         * calling ->ki_cancel.  We need the ctx_lock roundtrip here to
         * synchronize with them.  In the cancellation case the list_del_init
         * itself is not actually needed, but harmless so we keep it in to
         * avoid further branches in the fast path.
         */
        spin_lock_irq(&ctx->completion_lock);
        if (!mask && !READ_ONCE(poll->canceled)) {
                add_wait_queue(poll->head, &poll->wait);
                spin_unlock_irq(&ctx->completion_lock);
                return;
        }
        list_del_init(&req->list);
        io_poll_complete(ctx, req, mask);
        spin_unlock_irq(&ctx->completion_lock);

        io_cqring_ev_posted(ctx);
        io_put_req(req);
}

static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
                        void *key)
{
        struct io_poll_iocb *poll = container_of(wait, struct io_poll_iocb,
                                                        wait);
        struct io_kiocb *req = container_of(poll, struct io_kiocb, poll);
        struct io_ring_ctx *ctx = req->ctx;
        __poll_t mask = key_to_poll(key);
        unsigned long flags;

        /* for instances that support it check for an event match first: */
        if (mask && !(mask & poll->events))
                return 0;

        list_del_init(&poll->wait.entry);

        if (mask && spin_trylock_irqsave(&ctx->completion_lock, flags)) {
                list_del(&req->list);
                io_poll_complete(ctx, req, mask);
                spin_unlock_irqrestore(&ctx->completion_lock, flags);

                io_cqring_ev_posted(ctx);
                io_put_req(req);
        } else {
                queue_work(ctx->sqo_wq, &req->work);
        }

        return 1;
}

struct io_poll_table {
        struct poll_table_struct pt;
        struct io_kiocb *req;
        int error;
};

static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,
                               struct poll_table_struct *p)
{
        struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);

        if (unlikely(pt->req->poll.head)) {
                pt->error = -EINVAL;
                return;
        }

        pt->error = 0;
        pt->req->poll.head = head;
        add_wait_queue(head, &pt->req->poll.wait);
}

static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_poll_iocb *poll = &req->poll;
        struct io_ring_ctx *ctx = req->ctx;
        struct io_poll_table ipt;
        bool cancel = false;
        __poll_t mask;
        u16 events;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (sqe->addr || sqe->ioprio || sqe->off || sqe->len || sqe->buf_index)
                return -EINVAL;
        if (!poll->file)
                return -EBADF;

        INIT_WORK(&req->work, io_poll_complete_work);
        events = READ_ONCE(sqe->poll_events);
        poll->events = demangle_poll(events) | EPOLLERR | EPOLLHUP;

        poll->head = NULL;
        poll->done = false;
        poll->canceled = false;

        ipt.pt._qproc = io_poll_queue_proc;
        ipt.pt._key = poll->events;
        ipt.req = req;
        ipt.error = -EINVAL; /* same as no support for IOCB_CMD_POLL */

        /* initialized the list so that we can do list_empty checks */
        INIT_LIST_HEAD(&poll->wait.entry);
        init_waitqueue_func_entry(&poll->wait, io_poll_wake);

        INIT_LIST_HEAD(&req->list);

        mask = vfs_poll(poll->file, &ipt.pt) & poll->events;

        spin_lock_irq(&ctx->completion_lock);
        if (likely(poll->head)) {
                spin_lock(&poll->head->lock);
                if (unlikely(list_empty(&poll->wait.entry))) {
                        if (ipt.error)
                                cancel = true;
                        ipt.error = 0;
                        mask = 0;
                }
                if (mask || ipt.error)
                        list_del_init(&poll->wait.entry);
                else if (cancel)
                        WRITE_ONCE(poll->canceled, true);
                else if (!poll->done) /* actually waiting for an event */
                        list_add_tail(&req->list, &ctx->cancel_list);
                spin_unlock(&poll->head->lock);
        }
        if (mask) { /* no async, we'd stolen it */
                ipt.error = 0;
                io_poll_complete(ctx, req, mask);
        }
        spin_unlock_irq(&ctx->completion_lock);

        if (mask) {
                io_cqring_ev_posted(ctx);
                io_put_req(req);
        }
        return ipt.error;
}

static int io_req_defer(struct io_ring_ctx *ctx, struct io_kiocb *req,
                        const struct io_uring_sqe *sqe)
{
        struct io_uring_sqe *sqe_copy;

        if (!io_sequence_defer(ctx, req) && list_empty(&ctx->defer_list))
                return 0;

        sqe_copy = kmalloc(sizeof(*sqe_copy), GFP_KERNEL);
        if (!sqe_copy)
                return -EAGAIN;

        spin_lock_irq(&ctx->completion_lock);
        if (!io_sequence_defer(ctx, req) && list_empty(&ctx->defer_list)) {
                spin_unlock_irq(&ctx->completion_lock);
                kfree(sqe_copy);
                return 0;
        }

        memcpy(sqe_copy, sqe, sizeof(*sqe_copy));
        req->submit.sqe = sqe_copy;

        INIT_WORK(&req->work, io_sq_wq_submit_work);
        list_add_tail(&req->list, &ctx->defer_list);
        spin_unlock_irq(&ctx->completion_lock);
        return -EIOCBQUEUED;
}

static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
                           const struct sqe_submit *s, bool force_nonblock)
{
        int ret, opcode;

        req->user_data = READ_ONCE(s->sqe->user_data);

        if (unlikely(s->index >= ctx->sq_entries))
                return -EINVAL;

        opcode = READ_ONCE(s->sqe->opcode);
        switch (opcode) {
        case IORING_OP_NOP:
                ret = io_nop(req, req->user_data);
                break;
        case IORING_OP_READV:
                if (unlikely(s->sqe->buf_index))
                        return -EINVAL;
                ret = io_read(req, s, force_nonblock);
                break;
        case IORING_OP_WRITEV:
                if (unlikely(s->sqe->buf_index))
                        return -EINVAL;
                ret = io_write(req, s, force_nonblock);
                break;
        case IORING_OP_READ_FIXED:
                ret = io_read(req, s, force_nonblock);
                break;
        case IORING_OP_WRITE_FIXED:
                ret = io_write(req, s, force_nonblock);
                break;
        case IORING_OP_FSYNC:
                ret = io_fsync(req, s->sqe, force_nonblock);
                break;
        case IORING_OP_POLL_ADD:
                ret = io_poll_add(req, s->sqe);
                break;
        case IORING_OP_POLL_REMOVE:
                ret = io_poll_remove(req, s->sqe);
                break;
        case IORING_OP_SYNC_FILE_RANGE:
                ret = io_sync_file_range(req, s->sqe, force_nonblock);
                break;
        case IORING_OP_SENDMSG:
                ret = io_sendmsg(req, s->sqe, force_nonblock);
                break;
        case IORING_OP_RECVMSG:
                ret = io_recvmsg(req, s->sqe, force_nonblock);
                break;
        default:
                ret = -EINVAL;
                break;
        }

        if (ret)
                return ret;

        if (ctx->flags & IORING_SETUP_IOPOLL) {
                if (req->result == -EAGAIN)
                        return -EAGAIN;

                /* workqueue context doesn't hold uring_lock, grab it now */
                if (s->needs_lock)
                        mutex_lock(&ctx->uring_lock);
                io_iopoll_req_issued(req);
                if (s->needs_lock)
                        mutex_unlock(&ctx->uring_lock);
        }

        return 0;
}

static struct async_list *io_async_list_from_sqe(struct io_ring_ctx *ctx,
                                                 const struct io_uring_sqe *sqe)
{
        switch (sqe->opcode) {
        case IORING_OP_READV:
        case IORING_OP_READ_FIXED:
                return &ctx->pending_async[READ];
        case IORING_OP_WRITEV:
        case IORING_OP_WRITE_FIXED:
                return &ctx->pending_async[WRITE];
        default:
                return NULL;
        }
}

static inline bool io_sqe_needs_user(const struct io_uring_sqe *sqe)
{
        u8 opcode = READ_ONCE(sqe->opcode);

        return !(opcode == IORING_OP_READ_FIXED ||
                 opcode == IORING_OP_WRITE_FIXED);
}

static void io_sq_wq_submit_work(struct work_struct *work)
{
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);
        struct io_ring_ctx *ctx = req->ctx;
        struct mm_struct *cur_mm = NULL;
        struct async_list *async_list;
        LIST_HEAD(req_list);
        mm_segment_t old_fs;
        int ret;

        async_list = io_async_list_from_sqe(ctx, req->submit.sqe);
restart:
        do {
                struct sqe_submit *s = &req->submit;
                const struct io_uring_sqe *sqe = s->sqe;
                unsigned int flags = req->flags;

                /* Ensure we clear previously set non-block flag */
                req->rw.ki_flags &= ~IOCB_NOWAIT;

                ret = 0;
                if (io_sqe_needs_user(sqe) && !cur_mm) {
                        if (!mmget_not_zero(ctx->sqo_mm)) {
                                ret = -EFAULT;
                        } else {
                                cur_mm = ctx->sqo_mm;
                                use_mm(cur_mm);
                                old_fs = get_fs();
                                set_fs(USER_DS);
                        }
                }

                if (!ret) {
                        s->has_user = cur_mm != NULL;
                        s->needs_lock = true;
                        do {
                                ret = __io_submit_sqe(ctx, req, s, false);
                                /*
                                 * We can get EAGAIN for polled IO even though
                                 * we're forcing a sync submission from here,
                                 * since we can't wait for request slots on the
                                 * block side.
                                 */
                                if (ret != -EAGAIN)
                                        break;
                                cond_resched();
                        } while (1);
                }

                /* drop submission reference */
                io_put_req(req);

                if (ret) {
                        io_cqring_add_event(ctx, sqe->user_data, ret);
                        io_put_req(req);
                }

                /* async context always use a copy of the sqe */
                kfree(sqe);

                /* req from defer and link list needn't decrease async cnt */
                if (flags & (REQ_F_IO_DRAINED | REQ_F_LINK_DONE))
                        goto out;

                if (!async_list)
                        break;
                if (!list_empty(&req_list)) {
                        req = list_first_entry(&req_list, struct io_kiocb,
                                                list);
                        list_del(&req->list);
                        continue;
                }
                if (list_empty(&async_list->list))
                        break;

                req = NULL;
                spin_lock(&async_list->lock);
                if (list_empty(&async_list->list)) {
                        spin_unlock(&async_list->lock);
                        break;
                }
                list_splice_init(&async_list->list, &req_list);
                spin_unlock(&async_list->lock);

                req = list_first_entry(&req_list, struct io_kiocb, list);
                list_del(&req->list);
        } while (req);

        /*
         * Rare case of racing with a submitter. If we find the count has
         * dropped to zero AND we have pending work items, then restart
         * the processing. This is a tiny race window.
         */
        if (async_list) {
                ret = atomic_dec_return(&async_list->cnt);
                while (!ret && !list_empty(&async_list->list)) {
                        spin_lock(&async_list->lock);
                        atomic_inc(&async_list->cnt);
                        list_splice_init(&async_list->list, &req_list);
                        spin_unlock(&async_list->lock);

                        if (!list_empty(&req_list)) {
                                req = list_first_entry(&req_list,
                                                        struct io_kiocb, list);
                                list_del(&req->list);
                                goto restart;
                        }
                        ret = atomic_dec_return(&async_list->cnt);
                }
        }

out:
        if (cur_mm) {
                set_fs(old_fs);
                unuse_mm(cur_mm);
                mmput(cur_mm);
        }
}

/*
 * See if we can piggy back onto previously submitted work, that is still
 * running. We currently only allow this if the new request is sequential
 * to the previous one we punted.
 */
static bool io_add_to_prev_work(struct async_list *list, struct io_kiocb *req)
{
        bool ret = false;

        if (!list)
                return false;
        if (!(req->flags & REQ_F_SEQ_PREV))
                return false;
        if (!atomic_read(&list->cnt))
                return false;

        ret = true;
        spin_lock(&list->lock);
        list_add_tail(&req->list, &list->list);
        /*
         * Ensure we see a simultaneous modification from io_sq_wq_submit_work()
         */
        smp_mb();
        if (!atomic_read(&list->cnt)) {
                list_del_init(&req->list);
                ret = false;
        }
        spin_unlock(&list->lock);
        return ret;
}

static bool io_op_needs_file(const struct io_uring_sqe *sqe)
{
        int op = READ_ONCE(sqe->opcode);

        switch (op) {
        case IORING_OP_NOP:
        case IORING_OP_POLL_REMOVE:
                return false;
        default:
                return true;
        }
}

static int io_req_set_file(struct io_ring_ctx *ctx, const struct sqe_submit *s,
                           struct io_submit_state *state, struct io_kiocb *req)
{
        unsigned flags;
        int fd;

        flags = READ_ONCE(s->sqe->flags);
        fd = READ_ONCE(s->sqe->fd);

        if (flags & IOSQE_IO_DRAIN) {
                req->flags |= REQ_F_IO_DRAIN;
                req->sequence = ctx->cached_sq_head - 1;
        }

        if (!io_op_needs_file(s->sqe))
                return 0;

        if (flags & IOSQE_FIXED_FILE) {
                if (unlikely(!ctx->user_files ||
                    (unsigned) fd >= ctx->nr_user_files))
                        return -EBADF;
                req->file = ctx->user_files[fd];
                req->flags |= REQ_F_FIXED_FILE;
        } else {
                if (s->needs_fixed_file)
                        return -EBADF;
                req->file = io_file_get(state, fd);
                if (unlikely(!req->file))
                        return -EBADF;
        }

        return 0;
}

static int io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
                        struct sqe_submit *s)
{
        int ret;

        ret = io_req_defer(ctx, req, s->sqe);
        if (ret) {
                if (ret != -EIOCBQUEUED) {
                        io_free_req(req);
                        io_cqring_add_event(ctx, s->sqe->user_data, ret);
                }
                return 0;
        }

        ret = __io_submit_sqe(ctx, req, s, true);
        if (ret == -EAGAIN && !(req->flags & REQ_F_NOWAIT)) {
                struct io_uring_sqe *sqe_copy;

                sqe_copy = kmalloc(sizeof(*sqe_copy), GFP_KERNEL);
                if (sqe_copy) {
                        struct async_list *list;

                        memcpy(sqe_copy, s->sqe, sizeof(*sqe_copy));
                        s->sqe = sqe_copy;

                        memcpy(&req->submit, s, sizeof(*s));
                        list = io_async_list_from_sqe(ctx, s->sqe);
                        if (!io_add_to_prev_work(list, req)) {
                                if (list)
                                        atomic_inc(&list->cnt);
                                INIT_WORK(&req->work, io_sq_wq_submit_work);
                                queue_work(ctx->sqo_wq, &req->work);
                        }

                        /*
                         * Queued up for async execution, worker will release
                         * submit reference when the iocb is actually submitted.
                         */
                        return 0;
                }
        }

        /* drop submission reference */
        io_put_req(req);

        /* and drop final reference, if we failed */
        if (ret) {
                io_cqring_add_event(ctx, req->user_data, ret);
                if (req->flags & REQ_F_LINK)
                        req->flags |= REQ_F_FAIL_LINK;
                io_put_req(req);
        }

        return ret;
}

#define SQE_VALID_FLAGS (IOSQE_FIXED_FILE|IOSQE_IO_DRAIN|IOSQE_IO_LINK)

static void io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
                          struct io_submit_state *state, struct io_kiocb **link)
{
        struct io_uring_sqe *sqe_copy;
        struct io_kiocb *req;
        int ret;

        /* enforce forwards compatibility on users */
        if (unlikely(s->sqe->flags & ~SQE_VALID_FLAGS)) {
                ret = -EINVAL;
                goto err;
        }

        req = io_get_req(ctx, state);
        if (unlikely(!req)) {
                ret = -EAGAIN;
                goto err;
        }

        ret = io_req_set_file(ctx, s, state, req);
        if (unlikely(ret)) {
err_req:
                io_free_req(req);
err:
                io_cqring_add_event(ctx, s->sqe->user_data, ret);
                return;
        }

        /*
         * 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 (*link) {
                struct io_kiocb *prev = *link;

                sqe_copy = kmemdup(s->sqe, sizeof(*sqe_copy), GFP_KERNEL);
                if (!sqe_copy) {
                        ret = -EAGAIN;
                        goto err_req;
                }

                s->sqe = sqe_copy;
                memcpy(&req->submit, s, sizeof(*s));
                list_add_tail(&req->list, &prev->link_list);
        } else if (s->sqe->flags & IOSQE_IO_LINK) {
                req->flags |= REQ_F_LINK;

                memcpy(&req->submit, s, sizeof(*s));
                INIT_LIST_HEAD(&req->link_list);
                *link = req;
        } else {
                io_queue_sqe(ctx, req, s);
        }
}

/*
 * Batched submission is done, ensure local IO is flushed out.
 */
static void io_submit_state_end(struct io_submit_state *state)
{
        blk_finish_plug(&state->plug);
        io_file_put(state);
        if (state->free_reqs)
                kmem_cache_free_bulk(req_cachep, state->free_reqs,
                                        &state->reqs[state->cur_req]);
}

/*
 * Start submission side cache.
 */
static void io_submit_state_start(struct io_submit_state *state,
                                  struct io_ring_ctx *ctx, unsigned max_ios)
{
        blk_start_plug(&state->plug);
        state->free_reqs = 0;
        state->file = NULL;
        state->ios_left = max_ios;
}

static void io_commit_sqring(struct io_ring_ctx *ctx)
{
        struct io_sq_ring *ring = ctx->sq_ring;

        if (ctx->cached_sq_head != READ_ONCE(ring->r.head)) {
                /*
                 * 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(&ring->r.head, ctx->cached_sq_head);
        }
}

/*
 * Fetch an sqe, if one is available. Note that s->sqe will point 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_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
{
        struct io_sq_ring *ring = ctx->sq_ring;
        unsigned head;

        /*
         * 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 = ctx->cached_sq_head;
        /* make sure SQ entry isn't read before tail */
        if (head == smp_load_acquire(&ring->r.tail))
                return false;

        head = READ_ONCE(ring->array[head & ctx->sq_mask]);
        if (head < ctx->sq_entries) {
                s->index = head;
                s->sqe = &ctx->sq_sqes[head];
                ctx->cached_sq_head++;
                return true;
        }

        /* drop invalid entries */
        ctx->cached_sq_head++;
        ring->dropped++;
        return false;
}

static int io_submit_sqes(struct io_ring_ctx *ctx, struct sqe_submit *sqes,
                          unsigned int nr, bool has_user, bool mm_fault)
{
        struct io_submit_state state, *statep = NULL;
        struct io_kiocb *link = NULL;
        bool prev_was_link = false;
        int i, submitted = 0;

        if (nr > IO_PLUG_THRESHOLD) {
                io_submit_state_start(&state, ctx, nr);
                statep = &state;
        }

        for (i = 0; i < nr; i++) {
                /*
                 * If previous wasn't linked and we have a linked command,
                 * that's the end of the chain. Submit the previous link.
                 */
                if (!prev_was_link && link) {
                        io_queue_sqe(ctx, link, &link->submit);
                        link = NULL;
                }
                prev_was_link = (sqes[i].sqe->flags & IOSQE_IO_LINK) != 0;

                if (unlikely(mm_fault)) {
                        io_cqring_add_event(ctx, sqes[i].sqe->user_data,
                                                -EFAULT);
                } else {
                        sqes[i].has_user = has_user;
                        sqes[i].needs_lock = true;
                        sqes[i].needs_fixed_file = true;
                        io_submit_sqe(ctx, &sqes[i], statep, &link);
                        submitted++;
                }
        }

        if (link)
                io_queue_sqe(ctx, link, &link->submit);
        if (statep)
                io_submit_state_end(&state);

        return submitted;
}

static int io_sq_thread(void *data)
{
        struct sqe_submit sqes[IO_IOPOLL_BATCH];
        struct io_ring_ctx *ctx = data;
        struct mm_struct *cur_mm = NULL;
        mm_segment_t old_fs;
        DEFINE_WAIT(wait);
        unsigned inflight;
        unsigned long timeout;

        complete(&ctx->sqo_thread_started);

        old_fs = get_fs();
        set_fs(USER_DS);

        timeout = inflight = 0;
        while (!kthread_should_park()) {
                bool all_fixed, mm_fault = false;
                int i;

                if (inflight) {
                        unsigned nr_events = 0;

                        if (ctx->flags & IORING_SETUP_IOPOLL) {
                                io_iopoll_check(ctx, &nr_events, 0);
                        } else {
                                /*
                                 * Normal IO, just pretend everything completed.
                                 * We don't have to poll completions for that.
                                 */
                                nr_events = inflight;
                        }

                        inflight -= nr_events;
                        if (!inflight)
                                timeout = jiffies + ctx->sq_thread_idle;
                }

                if (!io_get_sqring(ctx, &sqes[0])) {
                        /*
                         * We're polling. If we're within the defined idle
                         * period, then let us spin without work before going
                         * to sleep.
                         */
                        if (inflight || !time_after(jiffies, timeout)) {
                                cpu_relax();
                                continue;
                        }

                        /*
                         * Drop cur_mm before scheduling, we can't hold it for
                         * long periods (or over schedule()). Do this before
                         * adding ourselves to the waitqueue, as the unuse/drop
                         * may sleep.
                         */
                        if (cur_mm) {
                                unuse_mm(cur_mm);
                                mmput(cur_mm);
                                cur_mm = NULL;
                        }

                        prepare_to_wait(&ctx->sqo_wait, &wait,
                                                TASK_INTERRUPTIBLE);

                        /* Tell userspace we may need a wakeup call */
                        ctx->sq_ring->flags |= IORING_SQ_NEED_WAKEUP;
                        /* make sure to read SQ tail after writing flags */
                        smp_mb();

                        if (!io_get_sqring(ctx, &sqes[0])) {
                                if (kthread_should_park()) {
                                        finish_wait(&ctx->sqo_wait, &wait);
                                        break;
                                }
                                if (signal_pending(current))
                                        flush_signals(current);
                                schedule();
                                finish_wait(&ctx->sqo_wait, &wait);

                                ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
                                continue;
                        }
                        finish_wait(&ctx->sqo_wait, &wait);

                        ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
                }

                i = 0;
                all_fixed = true;
                do {
                        if (all_fixed && io_sqe_needs_user(sqes[i].sqe))
                                all_fixed = false;

                        i++;
                        if (i == ARRAY_SIZE(sqes))
                                break;
                } while (io_get_sqring(ctx, &sqes[i]));

                /* Unless all new commands are FIXED regions, grab mm */
                if (!all_fixed && !cur_mm) {
                        mm_fault = !mmget_not_zero(ctx->sqo_mm);
                        if (!mm_fault) {
                                use_mm(ctx->sqo_mm);
                                cur_mm = ctx->sqo_mm;
                        }
                }

                inflight += io_submit_sqes(ctx, sqes, i, cur_mm != NULL,
                                                mm_fault);

                /* Commit SQ ring head once we've consumed all SQEs */
                io_commit_sqring(ctx);
        }

        set_fs(old_fs);
        if (cur_mm) {
                unuse_mm(cur_mm);
                mmput(cur_mm);
        }

        kthread_parkme();

        return 0;
}

static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
{
        struct io_submit_state state, *statep = NULL;
        struct io_kiocb *link = NULL;
        bool prev_was_link = false;
        int i, submit = 0;

        if (to_submit > IO_PLUG_THRESHOLD) {
                io_submit_state_start(&state, ctx, to_submit);
                statep = &state;
        }

        for (i = 0; i < to_submit; i++) {
                struct sqe_submit s;

                if (!io_get_sqring(ctx, &s))
                        break;

                /*
                 * If previous wasn't linked and we have a linked command,
                 * that's the end of the chain. Submit the previous link.
                 */
                if (!prev_was_link && link) {
                        io_queue_sqe(ctx, link, &link->submit);
                        link = NULL;
                }
                prev_was_link = (s.sqe->flags & IOSQE_IO_LINK) != 0;

                s.has_user = true;
                s.needs_lock = false;
                s.needs_fixed_file = false;
                submit++;
                io_submit_sqe(ctx, &s, statep, &link);
        }
        io_commit_sqring(ctx);

        if (link)
                io_queue_sqe(ctx, link, &link->submit);
        if (statep)
                io_submit_state_end(statep);

        return submit;
}

/*
 * 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 io_cq_ring *ring = ctx->cq_ring;
        int ret;

        if (io_cqring_events(ring) >= 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;
        }

        ret = wait_event_interruptible(ctx->wait, io_cqring_events(ring) >= min_events);
        restore_saved_sigmask_unless(ret == -ERESTARTSYS);
        if (ret == -ERESTARTSYS)
                ret = -EINTR;

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

static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
{
#if defined(CONFIG_UNIX)
        if (ctx->ring_sock) {
                struct sock *sock = ctx->ring_sock->sk;
                struct sk_buff *skb;

                while ((skb = skb_dequeue(&sock->sk_receive_queue)) != NULL)
                        kfree_skb(skb);
        }
#else
        int i;

        for (i = 0; i < ctx->nr_user_files; i++)
                fput(ctx->user_files[i]);
#endif
}

static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
{
        if (!ctx->user_files)
                return -ENXIO;

        __io_sqe_files_unregister(ctx);
        kfree(ctx->user_files);
        ctx->user_files = NULL;
        ctx->nr_user_files = 0;
        return 0;
}

static void io_sq_thread_stop(struct io_ring_ctx *ctx)
{
        if (ctx->sqo_thread) {
                wait_for_completion(&ctx->sqo_thread_started);
                /*
                 * The park is a bit of a work-around, without it we get
                 * warning spews on shutdown with SQPOLL set and affinity
                 * set to a single CPU.
                 */
                kthread_park(ctx->sqo_thread);
                kthread_stop(ctx->sqo_thread);
                ctx->sqo_thread = NULL;
        }
}

static void io_finish_async(struct io_ring_ctx *ctx)
{
        io_sq_thread_stop(ctx);

        if (ctx->sqo_wq) {
                destroy_workqueue(ctx->sqo_wq);
                ctx->sqo_wq = NULL;
        }
}

#if defined(CONFIG_UNIX)
static void io_destruct_skb(struct sk_buff *skb)
{
        struct io_ring_ctx *ctx = skb->sk->sk_user_data;

        io_finish_async(ctx);
        unix_destruct_scm(skb);
}

/*
 * Ensure the UNIX gc is aware of our file set, so we are certain that
 * the io_uring can be safely unregistered on process exit, even if we have
 * loops in the file referencing.
 */
static int __io_sqe_files_scm(struct io_ring_ctx *ctx, int nr, int offset)
{
        struct sock *sk = ctx->ring_sock->sk;
        struct scm_fp_list *fpl;
        struct sk_buff *skb;
        int i;

        if (!capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) {
                unsigned long inflight = ctx->user->unix_inflight + nr;

                if (inflight > task_rlimit(current, RLIMIT_NOFILE))
                        return -EMFILE;
        }

        fpl = kzalloc(sizeof(*fpl), GFP_KERNEL);
        if (!fpl)
                return -ENOMEM;

        skb = alloc_skb(0, GFP_KERNEL);
        if (!skb) {
                kfree(fpl);
                return -ENOMEM;
        }

        skb->sk = sk;
        skb->destructor = io_destruct_skb;

        fpl->user = get_uid(ctx->user);
        for (i = 0; i < nr; i++) {
                fpl->fp[i] = get_file(ctx->user_files[i + offset]);
                unix_inflight(fpl->user, fpl->fp[i]);
        }

        fpl->max = fpl->count = nr;
        UNIXCB(skb).fp = fpl;
        refcount_add(skb->truesize, &sk->sk_wmem_alloc);
        skb_queue_head(&sk->sk_receive_queue, skb);

        for (i = 0; i < nr; i++)
                fput(fpl->fp[i]);

        return 0;
}

/*
 * If UNIX sockets are enabled, fd passing can cause a reference cycle which
 * causes regular reference counting to break down. We rely on the UNIX
 * garbage collection to take care of this problem for us.
 */
static int io_sqe_files_scm(struct io_ring_ctx *ctx)
{
        unsigned left, total;
        int ret = 0;

        total = 0;
        left = ctx->nr_user_files;
        while (left) {
                unsigned this_files = min_t(unsigned, left, SCM_MAX_FD);

                ret = __io_sqe_files_scm(ctx, this_files, total);
                if (ret)
                        break;
                left -= this_files;
                total += this_files;
        }

        if (!ret)
                return 0;

        while (total < ctx->nr_user_files) {
                fput(ctx->user_files[total]);
                total++;
        }

        return ret;
}
#else
static int io_sqe_files_scm(struct io_ring_ctx *ctx)
{
        return 0;
}
#endif

static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
                                 unsigned nr_args)
{
        __s32 __user *fds = (__s32 __user *) arg;
        int fd, ret = 0;
        unsigned i;

        if (ctx->user_files)
                return -EBUSY;
        if (!nr_args)
                return -EINVAL;
        if (nr_args > IORING_MAX_FIXED_FILES)
                return -EMFILE;

        ctx->user_files = kcalloc(nr_args, sizeof(struct file *), GFP_KERNEL);
        if (!ctx->user_files)
                return -ENOMEM;

        for (i = 0; i < nr_args; i++) {
                ret = -EFAULT;
                if (copy_from_user(&fd, &fds[i], sizeof(fd)))
                        break;

                ctx->user_files[i] = fget(fd);

                ret = -EBADF;
                if (!ctx->user_files[i])
                        break;
                /*
                 * Don't allow io_uring instances to be registered. If UNIX
                 * isn't enabled, then this causes a reference cycle and this
                 * instance can never get freed. If UNIX is enabled we'll
                 * handle it just fine, but there's still no point in allowing
                 * a ring fd as it doesn't support regular read/write anyway.
                 */
                if (ctx->user_files[i]->f_op == &io_uring_fops) {
                        fput(ctx->user_files[i]);
                        break;
                }
                ctx->nr_user_files++;
                ret = 0;
        }

        if (ret) {
                for (i = 0; i < ctx->nr_user_files; i++)
                        fput(ctx->user_files[i]);

                kfree(ctx->user_files);
                ctx->user_files = NULL;
                ctx->nr_user_files = 0;
                return ret;
        }

        ret = io_sqe_files_scm(ctx);
        if (ret)
                io_sqe_files_unregister(ctx);

        return ret;
}

static int io_sq_offload_start(struct io_ring_ctx *ctx,
                               struct io_uring_params *p)
{
        int ret;

        init_waitqueue_head(&ctx->sqo_wait);
        mmgrab(current->mm);
        ctx->sqo_mm = current->mm;

        if (ctx->flags & IORING_SETUP_SQPOLL) {
                ret = -EPERM;
                if (!capable(CAP_SYS_ADMIN))
                        goto err;

                ctx->sq_thread_idle = msecs_to_jiffies(p->sq_thread_idle);
                if (!ctx->sq_thread_idle)
                        ctx->sq_thread_idle = HZ;

                if (p->flags & IORING_SETUP_SQ_AFF) {
                        int cpu = p->sq_thread_cpu;

                        ret = -EINVAL;
                        if (cpu >= nr_cpu_ids)
                                goto err;
                        if (!cpu_online(cpu))
                                goto err;

                        ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
                                                        ctx, cpu,
                                                        "io_uring-sq");
                } else {
                        ctx->sqo_thread = kthread_create(io_sq_thread, ctx,
                                                        "io_uring-sq");
                }
                if (IS_ERR(ctx->sqo_thread)) {
                        ret = PTR_ERR(ctx->sqo_thread);
                        ctx->sqo_thread = NULL;
                        goto err;
                }
                wake_up_process(ctx->sqo_thread);
        } else if (p->flags & IORING_SETUP_SQ_AFF) {
                /* Can't have SQ_AFF without SQPOLL */
                ret = -EINVAL;
                goto err;
        }

        /* Do QD, or 2 * CPUS, whatever is smallest */
        ctx->sqo_wq = alloc_workqueue("io_ring-wq", WQ_UNBOUND | WQ_FREEZABLE,
                        min(ctx->sq_entries - 1, 2 * num_online_cpus()));
        if (!ctx->sqo_wq) {
                ret = -ENOMEM;
                goto err;
        }

        return 0;
err:
        io_sq_thread_stop(ctx);
        mmdrop(ctx->sqo_mm);
        ctx->sqo_mm = NULL;
        return ret;
}

static void io_unaccount_mem(struct user_struct *user, unsigned long nr_pages)
{
        atomic_long_sub(nr_pages, &user->locked_vm);
}

static int io_account_mem(struct user_struct *user, unsigned long nr_pages)
{
        unsigned long page_limit, cur_pages, new_pages;

        /* Don't allow more pages than we can safely lock */
        page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;

        do {
                cur_pages = atomic_long_read(&user->locked_vm);
                new_pages = cur_pages + nr_pages;
                if (new_pages > page_limit)
                        return -ENOMEM;
        } while (atomic_long_cmpxchg(&user->locked_vm, cur_pages,
                                        new_pages) != cur_pages);

        return 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_flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP |
                                __GFP_NORETRY;

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

static unsigned long ring_pages(unsigned sq_entries, unsigned cq_entries)
{
        struct io_sq_ring *sq_ring;
        struct io_cq_ring *cq_ring;
        size_t bytes;

        bytes = struct_size(sq_ring, array, sq_entries);
        bytes += array_size(sizeof(struct io_uring_sqe), sq_entries);
        bytes += struct_size(cq_ring, cqes, cq_entries);

        return (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
}

static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
{
        int i, j;

        if (!ctx->user_bufs)
                return -ENXIO;

        for (i = 0; i < ctx->nr_user_bufs; i++) {
                struct io_mapped_ubuf *imu = &ctx->user_bufs[i];

                for (j = 0; j < imu->nr_bvecs; j++)
                        put_page(imu->bvec[j].bv_page);

                if (ctx->account_mem)
                        io_unaccount_mem(ctx->user, imu->nr_bvecs);
                kvfree(imu->bvec);
                imu->nr_bvecs = 0;
        }

        kfree(ctx->user_bufs);
        ctx->user_bufs = NULL;
        ctx->nr_user_bufs = 0;
        return 0;
}

static int io_copy_iov(struct io_ring_ctx *ctx, struct iovec *dst,
                       void __user *arg, unsigned index)
{
        struct iovec __user *src;

#ifdef CONFIG_COMPAT
        if (ctx->compat) {
                struct compat_iovec __user *ciovs;
                struct compat_iovec ciov;

                ciovs = (struct compat_iovec __user *) arg;
                if (copy_from_user(&ciov, &ciovs[index], sizeof(ciov)))
                        return -EFAULT;

                dst->iov_base = (void __user *) (unsigned long) ciov.iov_base;
                dst->iov_len = ciov.iov_len;
                return 0;
        }
#endif
        src = (struct iovec __user *) arg;
        if (copy_from_user(dst, &src[index], sizeof(*dst)))
                return -EFAULT;
        return 0;
}

static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
                                  unsigned nr_args)
{
        struct vm_area_struct **vmas = NULL;
        struct page **pages = NULL;
        int i, j, got_pages = 0;
        int ret = -EINVAL;

        if (ctx->user_bufs)
                return -EBUSY;
        if (!nr_args || nr_args > UIO_MAXIOV)
                return -EINVAL;

        ctx->user_bufs = kcalloc(nr_args, sizeof(struct io_mapped_ubuf),
                                        GFP_KERNEL);
        if (!ctx->user_bufs)
                return -ENOMEM;

        for (i = 0; i < nr_args; i++) {
                struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
                unsigned long off, start, end, ubuf;
                int pret, nr_pages;
                struct iovec iov;
                size_t size;

                ret = io_copy_iov(ctx, &iov, arg, i);
                if (ret)
                        goto err;

                /*
                 * Don't impose further limits on the size and buffer
                 * constraints here, we'll -EINVAL later when IO is
                 * submitted if they are wrong.
                 */
                ret = -EFAULT;
                if (!iov.iov_base || !iov.iov_len)
                        goto err;

                /* arbitrary limit, but we need something */
                if (iov.iov_len > SZ_1G)
                        goto err;

                ubuf = (unsigned long) iov.iov_base;
                end = (ubuf + iov.iov_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
                start = ubuf >> PAGE_SHIFT;
                nr_pages = end - start;

                if (ctx->account_mem) {
                        ret = io_account_mem(ctx->user, nr_pages);
                        if (ret)
                                goto err;
                }

                ret = 0;
                if (!pages || nr_pages > got_pages) {
                        kfree(vmas);
                        kfree(pages);
                        pages = kvmalloc_array(nr_pages, sizeof(struct page *),
                                                GFP_KERNEL);
                        vmas = kvmalloc_array(nr_pages,
                                        sizeof(struct vm_area_struct *),
                                        GFP_KERNEL);
                        if (!pages || !vmas) {
                                ret = -ENOMEM;
                                if (ctx->account_mem)
                                        io_unaccount_mem(ctx->user, nr_pages);
                                goto err;
                        }
                        got_pages = nr_pages;
                }

                imu->bvec = kvmalloc_array(nr_pages, sizeof(struct bio_vec),
                                                GFP_KERNEL);
                ret = -ENOMEM;
                if (!imu->bvec) {
                        if (ctx->account_mem)
                                io_unaccount_mem(ctx->user, nr_pages);
                        goto err;
                }

                ret = 0;
                down_read(&current->mm->mmap_sem);
                pret = get_user_pages(ubuf, nr_pages,
                                      FOLL_WRITE | FOLL_LONGTERM,
                                      pages, vmas);
                if (pret == nr_pages) {
                        /* don't support file backed memory */
                        for (j = 0; j < nr_pages; j++) {
                                struct vm_area_struct *vma = vmas[j];

                                if (vma->vm_file &&
                                    !is_file_hugepages(vma->vm_file)) {
                                        ret = -EOPNOTSUPP;
                                        break;
                                }
                        }
                } else {
                        ret = pret < 0 ? pret : -EFAULT;
                }
                up_read(&current->mm->mmap_sem);
                if (ret) {
                        /*
                         * if we did partial map, or found file backed vmas,
                         * release any pages we did get
                         */
                        if (pret > 0) {
                                for (j = 0; j < pret; j++)
                                        put_page(pages[j]);
                        }
                        if (ctx->account_mem)
                                io_unaccount_mem(ctx->user, nr_pages);
                        kvfree(imu->bvec);
                        goto err;
                }

                off = ubuf & ~PAGE_MASK;
                size = iov.iov_len;
                for (j = 0; j < nr_pages; j++) {
                        size_t vec_len;

                        vec_len = min_t(size_t, size, PAGE_SIZE - off);
                        imu->bvec[j].bv_page = pages[j];
                        imu->bvec[j].bv_len = vec_len;
                        imu->bvec[j].bv_offset = off;
                        off = 0;
                        size -= vec_len;
                }
                /* store original address for later verification */
                imu->ubuf = ubuf;
                imu->len = iov.iov_len;
                imu->nr_bvecs = nr_pages;

                ctx->nr_user_bufs++;
        }
        kvfree(pages);
        kvfree(vmas);
        return 0;
err:
        kvfree(pages);
        kvfree(vmas);
        io_sqe_buffer_unregister(ctx);
        return ret;
}

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

        if (ctx->cq_ev_fd)
                return -EBUSY;

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

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

        return 0;
}

static int io_eventfd_unregister(struct io_ring_ctx *ctx)
{
        if (ctx->cq_ev_fd) {
                eventfd_ctx_put(ctx->cq_ev_fd);
                ctx->cq_ev_fd = NULL;
                return 0;
        }

        return -ENXIO;
}

static void io_ring_ctx_free(struct io_ring_ctx *ctx)
{
        io_finish_async(ctx);
        if (ctx->sqo_mm)
                mmdrop(ctx->sqo_mm);

        io_iopoll_reap_events(ctx);
        io_sqe_buffer_unregister(ctx);
        io_sqe_files_unregister(ctx);
        io_eventfd_unregister(ctx);

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

        io_mem_free(ctx->sq_ring);
        io_mem_free(ctx->sq_sqes);
        io_mem_free(ctx->cq_ring);

        percpu_ref_exit(&ctx->refs);
        if (ctx->account_mem)
                io_unaccount_mem(ctx->user,
                                ring_pages(ctx->sq_entries, ctx->cq_entries));
        free_uid(ctx->user);
        kfree(ctx);
}

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

        poll_wait(file, &ctx->cq_wait, wait);
        /*
         * synchronizes with barrier from wq_has_sleeper call in
         * io_commit_cqring
         */
        smp_rmb();
        if (READ_ONCE(ctx->sq_ring->r.tail) - ctx->cached_sq_head !=
            ctx->sq_ring->ring_entries)
                mask |= EPOLLOUT | EPOLLWRNORM;
        if (READ_ONCE(ctx->cq_ring->r.head) != ctx->cached_cq_tail)
                mask |= EPOLLIN | EPOLLRDNORM;

        return mask;
}

static int io_uring_fasync(int fd, struct file *file, int on)
{
        struct io_ring_ctx *ctx = file->private_data;

        return fasync_helper(fd, file, on, &ctx->cq_fasync);
}

static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
{
        mutex_lock(&ctx->uring_lock);
        percpu_ref_kill(&ctx->refs);
        mutex_unlock(&ctx->uring_lock);

        io_poll_remove_all(ctx);
        io_iopoll_reap_events(ctx);
        wait_for_completion(&ctx->ctx_done);
        io_ring_ctx_free(ctx);
}

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;
}

static int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
{
        loff_t offset = (loff_t) vma->vm_pgoff << PAGE_SHIFT;
        unsigned long sz = vma->vm_end - vma->vm_start;
        struct io_ring_ctx *ctx = file->private_data;
        unsigned long pfn;
        struct page *page;
        void *ptr;

        switch (offset) {
        case IORING_OFF_SQ_RING:
                ptr = ctx->sq_ring;
                break;
        case IORING_OFF_SQES:
                ptr = ctx->sq_sqes;
                break;
        case IORING_OFF_CQ_RING:
                ptr = ctx->cq_ring;
                break;
        default:
                return -EINVAL;
        }

        page = virt_to_head_page(ptr);
        if (sz > (PAGE_SIZE << compound_order(page)))
                return -EINVAL;

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

SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
                u32, min_complete, u32, flags, const sigset_t __user *, sig,
                size_t, sigsz)
{
        struct io_ring_ctx *ctx;
        long ret = -EBADF;
        int submitted = 0;
        struct fd f;

        if (flags & ~(IORING_ENTER_GETEVENTS | IORING_ENTER_SQ_WAKEUP))
                return -EINVAL;

        f = fdget(fd);
        if (!f.file)
                return -EBADF;

        ret = -EOPNOTSUPP;
        if (f.file->f_op != &io_uring_fops)
                goto out_fput;

        ret = -ENXIO;
        ctx = f.file->private_data;
        if (!percpu_ref_tryget(&ctx->refs))
                goto out_fput;

        /*
         * 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.
         */
        if (ctx->flags & IORING_SETUP_SQPOLL) {
                if (flags & IORING_ENTER_SQ_WAKEUP)
                        wake_up(&ctx->sqo_wait);
                submitted = to_submit;
                goto out_ctx;
        }

        ret = 0;
        if (to_submit) {
                to_submit = min(to_submit, ctx->sq_entries);

                mutex_lock(&ctx->uring_lock);
                submitted = io_ring_submit(ctx, to_submit);
                mutex_unlock(&ctx->uring_lock);
        }
        if (flags & IORING_ENTER_GETEVENTS) {
                unsigned nr_events = 0;

                min_complete = min(min_complete, ctx->cq_entries);

                if (ctx->flags & IORING_SETUP_IOPOLL) {
                        ret = io_iopoll_check(ctx, &nr_events, min_complete);
                } else {
                        ret = io_cqring_wait(ctx, min_complete, sig, sigsz);
                }
        }

out_ctx:
        io_ring_drop_ctx_refs(ctx, 1);
out_fput:
        fdput(f);
        return submitted ? submitted : ret;
}

static const struct file_operations io_uring_fops = {
        .release        = io_uring_release,
        .mmap           = io_uring_mmap,
        .poll           = io_uring_poll,
        .fasync         = io_uring_fasync,
};

static int io_allocate_scq_urings(struct io_ring_ctx *ctx,
                                  struct io_uring_params *p)
{
        struct io_sq_ring *sq_ring;
        struct io_cq_ring *cq_ring;
        size_t size;

        sq_ring = io_mem_alloc(struct_size(sq_ring, array, p->sq_entries));
        if (!sq_ring)
                return -ENOMEM;

        ctx->sq_ring = sq_ring;
        sq_ring->ring_mask = p->sq_entries - 1;
        sq_ring->ring_entries = p->sq_entries;
        ctx->sq_mask = sq_ring->ring_mask;
        ctx->sq_entries = sq_ring->ring_entries;

        size = array_size(sizeof(struct io_uring_sqe), p->sq_entries);
        if (size == SIZE_MAX)
                return -EOVERFLOW;

        ctx->sq_sqes = io_mem_alloc(size);
        if (!ctx->sq_sqes)
                return -ENOMEM;

        cq_ring = io_mem_alloc(struct_size(cq_ring, cqes, p->cq_entries));
        if (!cq_ring)
                return -ENOMEM;

        ctx->cq_ring = cq_ring;
        cq_ring->ring_mask = p->cq_entries - 1;
        cq_ring->ring_entries = p->cq_entries;
        ctx->cq_mask = cq_ring->ring_mask;
        ctx->cq_entries = cq_ring->ring_entries;
        return 0;
}

/*
 * 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 int io_uring_get_fd(struct io_ring_ctx *ctx)
{
        struct file *file;
        int ret;

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

        ret = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
        if (ret < 0)
                goto err;

        file = anon_inode_getfile("[io_uring]", &io_uring_fops, ctx,
                                        O_RDWR | O_CLOEXEC);
        if (IS_ERR(file)) {
                put_unused_fd(ret);
                ret = PTR_ERR(file);
                goto err;
        }

#if defined(CONFIG_UNIX)
        ctx->ring_sock->file = file;
        ctx->ring_sock->sk->sk_user_data = ctx;
#endif
        fd_install(ret, file);
        return ret;
err:
#if defined(CONFIG_UNIX)
        sock_release(ctx->ring_sock);
        ctx->ring_sock = NULL;
#endif
        return ret;
}

static int io_uring_create(unsigned entries, struct io_uring_params *p)
{
        struct user_struct *user = NULL;
        struct io_ring_ctx *ctx;
        bool account_mem;
        int ret;

        if (!entries || entries > IORING_MAX_ENTRIES)
                return -EINVAL;

        /*
         * 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.
         */
        p->sq_entries = roundup_pow_of_two(entries);
        p->cq_entries = 2 * p->sq_entries;

        user = get_uid(current_user());
        account_mem = !capable(CAP_IPC_LOCK);

        if (account_mem) {
                ret = io_account_mem(user,
                                ring_pages(p->sq_entries, p->cq_entries));
                if (ret) {
                        free_uid(user);
                        return ret;
                }
        }

        ctx = io_ring_ctx_alloc(p);
        if (!ctx) {
                if (account_mem)
                        io_unaccount_mem(user, ring_pages(p->sq_entries,
                                                                p->cq_entries));
                free_uid(user);
                return -ENOMEM;
        }
        ctx->compat = in_compat_syscall();
        ctx->account_mem = account_mem;
        ctx->user = user;

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

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

        ret = io_uring_get_fd(ctx);
        if (ret < 0)
                goto err;

        memset(&p->sq_off, 0, sizeof(p->sq_off));
        p->sq_off.head = offsetof(struct io_sq_ring, r.head);
        p->sq_off.tail = offsetof(struct io_sq_ring, r.tail);
        p->sq_off.ring_mask = offsetof(struct io_sq_ring, ring_mask);
        p->sq_off.ring_entries = offsetof(struct io_sq_ring, ring_entries);
        p->sq_off.flags = offsetof(struct io_sq_ring, flags);
        p->sq_off.dropped = offsetof(struct io_sq_ring, dropped);
        p->sq_off.array = offsetof(struct io_sq_ring, array);

        memset(&p->cq_off, 0, sizeof(p->cq_off));
        p->cq_off.head = offsetof(struct io_cq_ring, r.head);
        p->cq_off.tail = offsetof(struct io_cq_ring, r.tail);
        p->cq_off.ring_mask = offsetof(struct io_cq_ring, ring_mask);
        p->cq_off.ring_entries = offsetof(struct io_cq_ring, ring_entries);
        p->cq_off.overflow = offsetof(struct io_cq_ring, overflow);
        p->cq_off.cqes = offsetof(struct io_cq_ring, cqes);
        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;
        long ret;
        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))
                return -EINVAL;

        ret = io_uring_create(entries, &p);
        if (ret < 0)
                return ret;

        if (copy_to_user(params, &p, sizeof(p)))
                return -EFAULT;

        return ret;
}

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

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're inside the ring mutex, if the ref is already dying, then
         * someone else killed the ctx or is already going through
         * io_uring_register().
         */
        if (percpu_ref_is_dying(&ctx->refs))
                return -ENXIO;

        percpu_ref_kill(&ctx->refs);

        /*
         * Drop uring mutex before waiting for references to exit. If another
         * thread is currently inside io_uring_enter() it might need to grab
         * the uring_lock to make progress. If we hold it here across the drain
         * wait, then we can deadlock. It's safe to drop the mutex here, since
         * no new references will come in after we've killed the percpu ref.
         */
        mutex_unlock(&ctx->uring_lock);
        wait_for_completion(&ctx->ctx_done);
        mutex_lock(&ctx->uring_lock);

        switch (opcode) {
        case IORING_REGISTER_BUFFERS:
                ret = io_sqe_buffer_register(ctx, arg, nr_args);
                break;
        case IORING_UNREGISTER_BUFFERS:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_sqe_buffer_unregister(ctx);
                break;
        case IORING_REGISTER_FILES:
                ret = io_sqe_files_register(ctx, arg, nr_args);
                break;
        case IORING_UNREGISTER_FILES:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_sqe_files_unregister(ctx);
                break;
        case IORING_REGISTER_EVENTFD:
                ret = -EINVAL;
                if (nr_args != 1)
                        break;
                ret = io_eventfd_register(ctx, arg);
                break;
        case IORING_UNREGISTER_EVENTFD:
                ret = -EINVAL;
                if (arg || nr_args)
                        break;
                ret = io_eventfd_unregister(ctx);
                break;
        default:
                ret = -EINVAL;
                break;
        }

        /* bring the ctx back to life */
        reinit_completion(&ctx->ctx_done);
        percpu_ref_reinit(&ctx->refs);
        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;

        f = fdget(fd);
        if (!f.file)
                return -EBADF;

        ret = -EOPNOTSUPP;
        if (f.file->f_op != &io_uring_fops)
                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);
out_fput:
        fdput(f);
        return ret;
}

static int __init io_uring_init(void)
{
        req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
        return 0;
};
__initcall(io_uring_init);