Merge tag 'upstream-5.5-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rw...

[linux-2.6-microblaze.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/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 <linux/highmem.h>

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

#include <uapi/linux/io_uring.h>

#include "internal.h"
#include "io-wq.h"

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

/*
 * Shift of 9 is 512 entries, or exactly one page on 64-bit archs
 */
#define IORING_FILE_TABLE_SHIFT 9
#define IORING_MAX_FILES_TABLE  (1U << IORING_FILE_TABLE_SHIFT)
#define IORING_FILE_TABLE_MASK  (IORING_MAX_FILES_TABLE - 1)
#define IORING_MAX_FIXED_FILES  (64 * IORING_MAX_FILES_TABLE)

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 offsets
 * IORING_OFF_SQ_RING and IORING_OFF_CQ_RING.
 *
 * The offsets to the member fields are published through struct
 * io_sqring_offsets when calling io_uring_setup.
 */
struct io_rings {
        /*
         * Head and tail offsets into the ring; the offsets need to be
         * masked to get valid indices.
         *
         * The kernel controls head of the sq ring and the tail of the cq ring,
         * and the application controls tail of the sq ring and the head of the
         * cq ring.
         */
        struct io_uring         sq, cq;
        /*
         * Bitmasks to apply to head and tail offsets (constant, equals
         * ring_entries - 1)
         */
        u32                     sq_ring_mask, cq_ring_mask;
        /* Ring sizes (constant, power of 2) */
        u32                     sq_ring_entries, cq_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                     sq_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                     sq_flags;
        /*
         * 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                     cq_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[] ____cacheline_aligned_in_smp;
};

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

struct fixed_file_table {
        struct file             **files;
};

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

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

                /*
                 * 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                     *sq_array;
                unsigned                cached_sq_head;
                unsigned                sq_entries;
                unsigned                sq_mask;
                unsigned                sq_thread_idle;
                unsigned                cached_sq_dropped;
                atomic_t                cached_cq_overflow;
                struct io_uring_sqe     *sq_sqes;

                struct list_head        defer_list;
                struct list_head        timeout_list;
                struct list_head        cq_overflow_list;

                wait_queue_head_t       inflight_wait;
        } ____cacheline_aligned_in_smp;

        struct io_rings *rings;

        /* IO offload */
        struct io_wq            *io_wq;
        struct task_struct      *sqo_thread;    /* if using sq thread polling */
        struct mm_struct        *sqo_mm;
        wait_queue_head_t       sqo_wait;

        /*
         * 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 fixed_file_table *file_table;
        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 cred             *creds;

        /* 0 is for ctx quiesce/reinit/free, 1 is for sqo_thread started */
        struct completion       *completions;

        /* if all else fails... */
        struct io_kiocb         *fallback_req;

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

        struct {
                unsigned                cached_cq_tail;
                unsigned                cq_entries;
                unsigned                cq_mask;
                atomic_t                cq_timeouts;
                struct wait_queue_head  cq_wait;
                struct fasync_struct    *cq_fasync;
                struct eventfd_ctx      *cq_ev_fd;
        } ____cacheline_aligned_in_smp;

        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 rb_root          cancel_tree;

                spinlock_t              inflight_lock;
                struct list_head        inflight_list;
        } ____cacheline_aligned_in_smp;
};

/*
 * 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;
};

struct io_timeout_data {
        struct io_kiocb                 *req;
        struct hrtimer                  timer;
        struct timespec64               ts;
        enum hrtimer_mode               mode;
        u32                             seq_offset;
};

struct io_timeout {
        struct file                     *file;
        struct io_timeout_data          *data;
};

/*
 * 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 io_timeout       timeout;
        };

        const struct io_uring_sqe       *sqe;
        struct file                     *ring_file;
        int                             ring_fd;
        bool                            has_user;
        bool                            in_async;
        bool                            needs_fixed_file;

        struct io_ring_ctx      *ctx;
        union {
                struct list_head        list;
                struct rb_node          rb_node;
        };
        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_LINK_NEXT         8       /* already grabbed next link */
#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_TIMEOUT      128     /* has linked timeout */
#define REQ_F_FAIL_LINK         256     /* fail rest of links */
#define REQ_F_DRAIN_LINK        512     /* link should be fully drained */
#define REQ_F_TIMEOUT           1024    /* timeout request */
#define REQ_F_ISREG             2048    /* regular file */
#define REQ_F_MUST_PUNT         4096    /* must be punted even for NONBLOCK */
#define REQ_F_TIMEOUT_NOSEQ     8192    /* no timeout sequence */
#define REQ_F_INFLIGHT          16384   /* on inflight list */
#define REQ_F_COMP_LOCKED       32768   /* completion under lock */
#define REQ_F_FREE_SQE          65536   /* free sqe if not async queued */
        u64                     user_data;
        u32                     result;
        u32                     sequence;

        struct list_head        inflight_entry;

        struct io_wq_work       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_wq_submit_work(struct io_wq_work **workptr);
static void io_cqring_fill_event(struct io_kiocb *req, long res);
static void __io_free_req(struct io_kiocb *req);
static void io_put_req(struct io_kiocb *req);
static void io_double_put_req(struct io_kiocb *req);
static void __io_double_put_req(struct io_kiocb *req);
static struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req);
static void io_queue_linked_timeout(struct io_kiocb *req);

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->completions[0]);
}

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

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

        ctx->fallback_req = kmem_cache_alloc(req_cachep, GFP_KERNEL);
        if (!ctx->fallback_req)
                goto err;

        ctx->completions = kmalloc(2 * sizeof(struct completion), GFP_KERNEL);
        if (!ctx->completions)
                goto err;

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

        ctx->flags = p->flags;
        init_waitqueue_head(&ctx->cq_wait);
        INIT_LIST_HEAD(&ctx->cq_overflow_list);
        init_completion(&ctx->completions[0]);
        init_completion(&ctx->completions[1]);
        mutex_init(&ctx->uring_lock);
        init_waitqueue_head(&ctx->wait);
        spin_lock_init(&ctx->completion_lock);
        INIT_LIST_HEAD(&ctx->poll_list);
        ctx->cancel_tree = RB_ROOT;
        INIT_LIST_HEAD(&ctx->defer_list);
        INIT_LIST_HEAD(&ctx->timeout_list);
        init_waitqueue_head(&ctx->inflight_wait);
        spin_lock_init(&ctx->inflight_lock);
        INIT_LIST_HEAD(&ctx->inflight_list);
        return ctx;
err:
        if (ctx->fallback_req)
                kmem_cache_free(req_cachep, ctx->fallback_req);
        kfree(ctx->completions);
        kfree(ctx);
        return NULL;
}

static inline bool __req_need_defer(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;

        return req->sequence != ctx->cached_cq_tail + ctx->cached_sq_dropped
                                        + atomic_read(&ctx->cached_cq_overflow);
}

static inline bool req_need_defer(struct io_kiocb *req)
{
        if ((req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) == REQ_F_IO_DRAIN)
                return __req_need_defer(req);

        return false;
}

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

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

        return NULL;
}

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

        req = list_first_entry_or_null(&ctx->timeout_list, struct io_kiocb, list);
        if (req) {
                if (req->flags & REQ_F_TIMEOUT_NOSEQ)
                        return NULL;
                if (!__req_need_defer(req)) {
                        list_del_init(&req->list);
                        return req;
                }
        }

        return NULL;
}

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

        if (ctx->cached_cq_tail != READ_ONCE(rings->cq.tail)) {
                /* order cqe stores with ring update */
                smp_store_release(&rings->cq.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 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 inline bool io_prep_async_work(struct io_kiocb *req,
                                      struct io_kiocb **link)
{
        bool do_hashed = false;

        if (req->sqe) {
                switch (req->sqe->opcode) {
                case IORING_OP_WRITEV:
                case IORING_OP_WRITE_FIXED:
                        do_hashed = true;
                        /* fall-through */
                case IORING_OP_READV:
                case IORING_OP_READ_FIXED:
                case IORING_OP_SENDMSG:
                case IORING_OP_RECVMSG:
                case IORING_OP_ACCEPT:
                case IORING_OP_POLL_ADD:
                case IORING_OP_CONNECT:
                        /*
                         * We know REQ_F_ISREG is not set on some of these
                         * opcodes, but this enables us to keep the check in
                         * just one place.
                         */
                        if (!(req->flags & REQ_F_ISREG))
                                req->work.flags |= IO_WQ_WORK_UNBOUND;
                        break;
                }
                if (io_sqe_needs_user(req->sqe))
                        req->work.flags |= IO_WQ_WORK_NEEDS_USER;
        }

        *link = io_prep_linked_timeout(req);
        return do_hashed;
}

static inline void io_queue_async_work(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_kiocb *link;
        bool do_hashed;

        do_hashed = io_prep_async_work(req, &link);

        trace_io_uring_queue_async_work(ctx, do_hashed, req, &req->work,
                                        req->flags);
        if (!do_hashed) {
                io_wq_enqueue(ctx->io_wq, &req->work);
        } else {
                io_wq_enqueue_hashed(ctx->io_wq, &req->work,
                                        file_inode(req->file));
        }

        if (link)
                io_queue_linked_timeout(link);
}

static void io_kill_timeout(struct io_kiocb *req)
{
        int ret;

        ret = hrtimer_try_to_cancel(&req->timeout.data->timer);
        if (ret != -1) {
                atomic_inc(&req->ctx->cq_timeouts);
                list_del_init(&req->list);
                io_cqring_fill_event(req, 0);
                io_put_req(req);
        }
}

static void io_kill_timeouts(struct io_ring_ctx *ctx)
{
        struct io_kiocb *req, *tmp;

        spin_lock_irq(&ctx->completion_lock);
        list_for_each_entry_safe(req, tmp, &ctx->timeout_list, list)
                io_kill_timeout(req);
        spin_unlock_irq(&ctx->completion_lock);
}

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

        while ((req = io_get_timeout_req(ctx)) != NULL)
                io_kill_timeout(req);

        __io_commit_cqring(ctx);

        while ((req = io_get_deferred_req(ctx)) != NULL) {
                req->flags |= REQ_F_IO_DRAINED;
                io_queue_async_work(req);
        }
}

static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx)
{
        struct io_rings *rings = ctx->rings;
        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(rings->cq.head) == rings->cq_ring_entries)
                return NULL;

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

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);
}

/* Returns true if there are no backlogged entries after the flush */
static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
{
        struct io_rings *rings = ctx->rings;
        struct io_uring_cqe *cqe;
        struct io_kiocb *req;
        unsigned long flags;
        LIST_HEAD(list);

        if (!force) {
                if (list_empty_careful(&ctx->cq_overflow_list))
                        return true;
                if ((ctx->cached_cq_tail - READ_ONCE(rings->cq.head) ==
                    rings->cq_ring_entries))
                        return false;
        }

        spin_lock_irqsave(&ctx->completion_lock, flags);

        /* if force is set, the ring is going away. always drop after that */
        if (force)
                ctx->cq_overflow_flushed = true;

        cqe = NULL;
        while (!list_empty(&ctx->cq_overflow_list)) {
                cqe = io_get_cqring(ctx);
                if (!cqe && !force)
                        break;

                req = list_first_entry(&ctx->cq_overflow_list, struct io_kiocb,
                                                list);
                list_move(&req->list, &list);
                if (cqe) {
                        WRITE_ONCE(cqe->user_data, req->user_data);
                        WRITE_ONCE(cqe->res, req->result);
                        WRITE_ONCE(cqe->flags, 0);
                } else {
                        WRITE_ONCE(ctx->rings->cq_overflow,
                                atomic_inc_return(&ctx->cached_cq_overflow));
                }
        }

        io_commit_cqring(ctx);
        spin_unlock_irqrestore(&ctx->completion_lock, flags);
        io_cqring_ev_posted(ctx);

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

        return cqe != NULL;
}

static void io_cqring_fill_event(struct io_kiocb *req, long res)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_uring_cqe *cqe;

        trace_io_uring_complete(ctx, req->user_data, res);

        /*
         * 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 (likely(cqe)) {
                WRITE_ONCE(cqe->user_data, req->user_data);
                WRITE_ONCE(cqe->res, res);
                WRITE_ONCE(cqe->flags, 0);
        } else if (ctx->cq_overflow_flushed) {
                WRITE_ONCE(ctx->rings->cq_overflow,
                                atomic_inc_return(&ctx->cached_cq_overflow));
        } else {
                refcount_inc(&req->refs);
                req->result = res;
                list_add_tail(&req->list, &ctx->cq_overflow_list);
        }
}

static void io_cqring_add_event(struct io_kiocb *req, long res)
{
        struct io_ring_ctx *ctx = req->ctx;
        unsigned long flags;

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

        io_cqring_ev_posted(ctx);
}

static inline bool io_is_fallback_req(struct io_kiocb *req)
{
        return req == (struct io_kiocb *)
                        ((unsigned long) req->ctx->fallback_req & ~1UL);
}

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

        req = ctx->fallback_req;
        if (!test_and_set_bit_lock(0, (unsigned long *) ctx->fallback_req))
                return req;

        return NULL;
}

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 fallback;
        } 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 fallback;
                        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++;
        }

got_it:
        req->ring_file = NULL;
        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;
        INIT_IO_WORK(&req->work, io_wq_submit_work);
        return req;
fallback:
        req = io_get_fallback_req(ctx);
        if (req)
                goto got_it;
        percpu_ref_put(&ctx->refs);
        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);
                percpu_ref_put_many(&ctx->refs, *nr);
                *nr = 0;
        }
}

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

        if (req->flags & REQ_F_FREE_SQE)
                kfree(req->sqe);
        if (req->file && !(req->flags & REQ_F_FIXED_FILE))
                fput(req->file);
        if (req->flags & REQ_F_INFLIGHT) {
                unsigned long flags;

                spin_lock_irqsave(&ctx->inflight_lock, flags);
                list_del(&req->inflight_entry);
                if (waitqueue_active(&ctx->inflight_wait))
                        wake_up(&ctx->inflight_wait);
                spin_unlock_irqrestore(&ctx->inflight_lock, flags);
        }
        if (req->flags & REQ_F_TIMEOUT)
                kfree(req->timeout.data);
        percpu_ref_put(&ctx->refs);
        if (likely(!io_is_fallback_req(req)))
                kmem_cache_free(req_cachep, req);
        else
                clear_bit_unlock(0, (unsigned long *) ctx->fallback_req);
}

static bool io_link_cancel_timeout(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        int ret;

        ret = hrtimer_try_to_cancel(&req->timeout.data->timer);
        if (ret != -1) {
                io_cqring_fill_event(req, -ECANCELED);
                io_commit_cqring(ctx);
                req->flags &= ~REQ_F_LINK;
                io_put_req(req);
                return true;
        }

        return false;
}

static void io_req_link_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_kiocb *nxt;
        bool wake_ev = false;

        /* Already got next link */
        if (req->flags & REQ_F_LINK_NEXT)
                return;

        /*
         * 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);
        while (nxt) {
                list_del_init(&nxt->list);

                if ((req->flags & REQ_F_LINK_TIMEOUT) &&
                    (nxt->flags & REQ_F_TIMEOUT)) {
                        wake_ev |= io_link_cancel_timeout(nxt);
                        nxt = list_first_entry_or_null(&req->link_list,
                                                        struct io_kiocb, list);
                        req->flags &= ~REQ_F_LINK_TIMEOUT;
                        continue;
                }
                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;
                }

                *nxtptr = nxt;
                break;
        }

        req->flags |= REQ_F_LINK_NEXT;
        if (wake_ev)
                io_cqring_ev_posted(ctx);
}

/*
 * Called if REQ_F_LINK is set, and we fail the head request
 */
static void io_fail_links(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_kiocb *link;
        unsigned long flags;

        spin_lock_irqsave(&ctx->completion_lock, flags);

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

                trace_io_uring_fail_link(req, link);

                if ((req->flags & REQ_F_LINK_TIMEOUT) &&
                    link->sqe->opcode == IORING_OP_LINK_TIMEOUT) {
                        io_link_cancel_timeout(link);
                } else {
                        io_cqring_fill_event(link, -ECANCELED);
                        __io_double_put_req(link);
                }
                req->flags &= ~REQ_F_LINK_TIMEOUT;
        }

        io_commit_cqring(ctx);
        spin_unlock_irqrestore(&ctx->completion_lock, flags);
        io_cqring_ev_posted(ctx);
}

static void io_req_find_next(struct io_kiocb *req, struct io_kiocb **nxt)
{
        if (likely(!(req->flags & REQ_F_LINK)))
                return;

        /*
         * 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_FAIL_LINK) {
                io_fail_links(req);
        } else if ((req->flags & (REQ_F_LINK_TIMEOUT | REQ_F_COMP_LOCKED)) ==
                        REQ_F_LINK_TIMEOUT) {
                struct io_ring_ctx *ctx = req->ctx;
                unsigned long flags;

                /*
                 * If this is a timeout link, we could be racing with the
                 * timeout timer. Grab the completion lock for this case to
                 * protect against that.
                 */
                spin_lock_irqsave(&ctx->completion_lock, flags);
                io_req_link_next(req, nxt);
                spin_unlock_irqrestore(&ctx->completion_lock, flags);
        } else {
                io_req_link_next(req, nxt);
        }
}

static void io_free_req(struct io_kiocb *req)
{
        struct io_kiocb *nxt = NULL;

        io_req_find_next(req, &nxt);
        __io_free_req(req);

        if (nxt)
                io_queue_async_work(nxt);
}

/*
 * Drop reference to request, return next in chain (if there is one) if this
 * was the last reference to this request.
 */
__attribute__((nonnull))
static void io_put_req_find_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
{
        io_req_find_next(req, nxtptr);

        if (refcount_dec_and_test(&req->refs))
                __io_free_req(req);
}

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

/*
 * Must only be used if we don't need to care about links, usually from
 * within the completion handling itself.
 */
static void __io_double_put_req(struct io_kiocb *req)
{
        /* drop both submit and complete references */
        if (refcount_sub_and_test(2, &req->refs))
                __io_free_req(req);
}

static void io_double_put_req(struct io_kiocb *req)
{
        /* drop both submit and complete references */
        if (refcount_sub_and_test(2, &req->refs))
                io_free_req(req);
}

static unsigned io_cqring_events(struct io_ring_ctx *ctx, bool noflush)
{
        struct io_rings *rings = ctx->rings;

        /*
         * noflush == true is from the waitqueue handler, just ensure we wake
         * up the task, and the next invocation will flush the entries. We
         * cannot safely to it from here.
         */
        if (noflush && !list_empty(&ctx->cq_overflow_list))
                return -1U;

        io_cqring_overflow_flush(ctx, false);

        /* See comment at the top of this file */
        smp_rmb();
        return READ_ONCE(rings->cq.tail) - READ_ONCE(rings->cq.head);
}

static inline unsigned int io_sqring_entries(struct io_ring_ctx *ctx)
{
        struct io_rings *rings = ctx->rings;

        /* make sure SQ entry isn't read before tail */
        return smp_load_acquire(&rings->sq.tail) - ctx->cached_sq_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(req, 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_FREE_SQE)) ==
                            REQ_F_FIXED_FILE) && !io_is_fallback_req(req)) {
                                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) && !need_resched()) {
                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);

                /*
                 * Ensure we allow local-to-the-cpu processing to take place,
                 * in this case we need to ensure that we reap all events.
                 */
                cond_resched();
        }
        mutex_unlock(&ctx->uring_lock);
}

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

        return ret;
}

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

        /*
         * 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);
        ret = __io_iopoll_check(ctx, nr_events, min);
        mutex_unlock(&ctx->uring_lock);
        return ret;
}

static void kiocb_end_write(struct io_kiocb *req)
{
        /*
         * Tell lockdep we inherited freeze protection from submission
         * thread.
         */
        if (req->flags & REQ_F_ISREG) {
                struct inode *inode = file_inode(req->file);

                __sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
        }
        file_end_write(req->file);
}

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

        if (kiocb->ki_flags & IOCB_WRITE)
                kiocb_end_write(req);

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

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

        io_complete_rw_common(kiocb, res);
        io_put_req(req);
}

static struct io_kiocb *__io_complete_rw(struct kiocb *kiocb, long res)
{
        struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
        struct io_kiocb *nxt = NULL;

        io_complete_rw_common(kiocb, res);
        io_put_req_find_next(req, &nxt);

        return nxt;
}

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

        if (kiocb->ki_flags & IOCB_WRITE)
                kiocb_end_write(req);

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

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

        if (S_ISREG(file_inode(req->file)->i_mode))
                req->flags |= REQ_F_ISREG;

        /*
         * If the file doesn't support async, mark it as REQ_F_MUST_PUNT so
         * we know to async punt it even if it was opened O_NONBLOCK
         */
        if (force_nonblock && !io_file_supports_async(req->file)) {
                req->flags |= REQ_F_MUST_PUNT;
                return -EAGAIN;
        }

        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->file->f_flags & O_NONBLOCK))
                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;
                req->result = 0;
        } 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 void kiocb_done(struct kiocb *kiocb, ssize_t ret, struct io_kiocb **nxt,
                       bool in_async)
{
        if (in_async && ret >= 0 && kiocb->ki_complete == io_complete_rw)
                *nxt = __io_complete_rw(kiocb, ret);
        else
                io_rw_done(kiocb, ret);
}

static ssize_t 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 len;
}

static ssize_t io_import_iovec(int rw, struct io_kiocb *req,
                               struct iovec **iovec, struct iov_iter *iter)
{
        const struct io_uring_sqe *sqe = req->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) {
                *iovec = NULL;
                return io_import_fixed(req->ctx, rw, sqe, iter);
        }

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

#ifdef CONFIG_COMPAT
        if (req->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);
}

/*
 * For files that don't have ->read_iter() and ->write_iter(), handle them
 * by looping over ->read() or ->write() manually.
 */
static ssize_t loop_rw_iter(int rw, struct file *file, struct kiocb *kiocb,
                           struct iov_iter *iter)
{
        ssize_t ret = 0;

        /*
         * Don't support polled IO through this interface, and we can't
         * support non-blocking either. For the latter, this just causes
         * the kiocb to be handled from an async context.
         */
        if (kiocb->ki_flags & IOCB_HIPRI)
                return -EOPNOTSUPP;
        if (kiocb->ki_flags & IOCB_NOWAIT)
                return -EAGAIN;

        while (iov_iter_count(iter)) {
                struct iovec iovec;
                ssize_t nr;

                if (!iov_iter_is_bvec(iter)) {
                        iovec = iov_iter_iovec(iter);
                } else {
                        /* fixed buffers import bvec */
                        iovec.iov_base = kmap(iter->bvec->bv_page)
                                                + iter->iov_offset;
                        iovec.iov_len = min(iter->count,
                                        iter->bvec->bv_len - iter->iov_offset);
                }

                if (rw == READ) {
                        nr = file->f_op->read(file, iovec.iov_base,
                                              iovec.iov_len, &kiocb->ki_pos);
                } else {
                        nr = file->f_op->write(file, iovec.iov_base,
                                               iovec.iov_len, &kiocb->ki_pos);
                }

                if (iov_iter_is_bvec(iter))
                        kunmap(iter->bvec->bv_page);

                if (nr < 0) {
                        if (!ret)
                                ret = nr;
                        break;
                }
                ret += nr;
                if (nr != iovec.iov_len)
                        break;
                iov_iter_advance(iter, nr);
        }

        return ret;
}

static int io_read(struct io_kiocb *req, struct io_kiocb **nxt,
                   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, force_nonblock);
        if (ret)
                return ret;
        file = kiocb->ki_filp;

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

        ret = io_import_iovec(READ, req, &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;

                if (file->f_op->read_iter)
                        ret2 = call_read_iter(file, kiocb, &iter);
                else
                        ret2 = loop_rw_iter(READ, 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 && !(req->flags & REQ_F_NOWAIT) &&
                    (req->flags & REQ_F_ISREG) &&
                    ret2 > 0 && ret2 < read_size)
                        ret2 = -EAGAIN;
                /* Catch -EAGAIN return for forced non-blocking submission */
                if (!force_nonblock || ret2 != -EAGAIN)
                        kiocb_done(kiocb, ret2, nxt, req->in_async);
                else
                        ret = -EAGAIN;
        }
        kfree(iovec);
        return ret;
}

static int io_write(struct io_kiocb *req, struct io_kiocb **nxt,
                    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, force_nonblock);
        if (ret)
                return ret;

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

        ret = io_import_iovec(WRITE, req, &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))
                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 (req->flags & REQ_F_ISREG) {
                        __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;

                if (file->f_op->write_iter)
                        ret2 = call_write_iter(file, kiocb, &iter);
                else
                        ret2 = loop_rw_iter(WRITE, file, kiocb, &iter);
                if (!force_nonblock || ret2 != -EAGAIN)
                        kiocb_done(kiocb, ret2, nxt, req->in_async);
                else
                        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)
{
        struct io_ring_ctx *ctx = req->ctx;

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

        io_cqring_add_event(req, 0);
        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,
                    struct io_kiocb **nxt, 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, ret);
        io_put_req_find_next(req, nxt);
        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,
                              struct io_kiocb **nxt,
                              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, ret);
        io_put_req_find_next(req, nxt);
        return 0;
}

#if defined(CONFIG_NET)
static int io_send_recvmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                           struct io_kiocb **nxt, 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, ret);
        if (ret < 0 && (req->flags & REQ_F_LINK))
                req->flags |= REQ_F_FAIL_LINK;
        io_put_req_find_next(req, nxt);
        return 0;
}
#endif

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

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

static int io_accept(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                     struct io_kiocb **nxt, bool force_nonblock)
{
#if defined(CONFIG_NET)
        struct sockaddr __user *addr;
        int __user *addr_len;
        unsigned file_flags;
        int flags, ret;

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

        addr = (struct sockaddr __user *) (unsigned long) READ_ONCE(sqe->addr);
        addr_len = (int __user *) (unsigned long) READ_ONCE(sqe->addr2);
        flags = READ_ONCE(sqe->accept_flags);
        file_flags = force_nonblock ? O_NONBLOCK : 0;

        ret = __sys_accept4_file(req->file, file_flags, addr, addr_len, flags);
        if (ret == -EAGAIN && force_nonblock) {
                req->work.flags |= IO_WQ_WORK_NEEDS_FILES;
                return -EAGAIN;
        }
        if (ret == -ERESTARTSYS)
                ret = -EINTR;
        if (ret < 0 && (req->flags & REQ_F_LINK))
                req->flags |= REQ_F_FAIL_LINK;
        io_cqring_add_event(req, ret);
        io_put_req_find_next(req, nxt);
        return 0;
#else
        return -EOPNOTSUPP;
#endif
}

static int io_connect(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                      struct io_kiocb **nxt, bool force_nonblock)
{
#if defined(CONFIG_NET)
        struct sockaddr __user *addr;
        unsigned file_flags;
        int addr_len, ret;

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

        addr = (struct sockaddr __user *) (unsigned long) READ_ONCE(sqe->addr);
        addr_len = READ_ONCE(sqe->addr2);
        file_flags = force_nonblock ? O_NONBLOCK : 0;

        ret = __sys_connect_file(req->file, addr, addr_len, file_flags);
        if (ret == -EAGAIN && force_nonblock)
                return -EAGAIN;
        if (ret == -ERESTARTSYS)
                ret = -EINTR;
        if (ret < 0 && (req->flags & REQ_F_LINK))
                req->flags |= REQ_F_FAIL_LINK;
        io_cqring_add_event(req, ret);
        io_put_req_find_next(req, nxt);
        return 0;
#else
        return -EOPNOTSUPP;
#endif
}

static inline void io_poll_remove_req(struct io_kiocb *req)
{
        if (!RB_EMPTY_NODE(&req->rb_node)) {
                rb_erase(&req->rb_node, &req->ctx->cancel_tree);
                RB_CLEAR_NODE(&req->rb_node);
        }
}

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);
                io_queue_async_work(req);
        }
        spin_unlock(&poll->head->lock);
        io_poll_remove_req(req);
}

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

        spin_lock_irq(&ctx->completion_lock);
        while ((node = rb_first(&ctx->cancel_tree)) != NULL) {
                req = rb_entry(node, struct io_kiocb, rb_node);
                io_poll_remove_one(req);
        }
        spin_unlock_irq(&ctx->completion_lock);
}

static int io_poll_cancel(struct io_ring_ctx *ctx, __u64 sqe_addr)
{
        struct rb_node *p, *parent = NULL;
        struct io_kiocb *req;

        p = ctx->cancel_tree.rb_node;
        while (p) {
                parent = p;
                req = rb_entry(parent, struct io_kiocb, rb_node);
                if (sqe_addr < req->user_data) {
                        p = p->rb_left;
                } else if (sqe_addr > req->user_data) {
                        p = p->rb_right;
                } else {
                        io_poll_remove_one(req);
                        return 0;
                }
        }

        return -ENOENT;
}

/*
 * 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;
        int ret;

        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);
        ret = io_poll_cancel(ctx, READ_ONCE(sqe->addr));
        spin_unlock_irq(&ctx->completion_lock);

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

static void io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
{
        struct io_ring_ctx *ctx = req->ctx;

        req->poll.done = true;
        kfree(req->poll.wait);
        if (error)
                io_cqring_fill_event(req, error);
        else
                io_cqring_fill_event(req, mangle_poll(mask));
        io_commit_cqring(ctx);
}

static void io_poll_complete_work(struct io_wq_work **workptr)
{
        struct io_wq_work *work = *workptr;
        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;
        struct io_kiocb *nxt = NULL;
        __poll_t mask = 0;
        int ret = 0;

        if (work->flags & IO_WQ_WORK_CANCEL) {
                WRITE_ONCE(poll->canceled, true);
                ret = -ECANCELED;
        } else if (READ_ONCE(poll->canceled)) {
                ret = -ECANCELED;
        }

        if (ret != -ECANCELED)
                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 && ret != -ECANCELED) {
                add_wait_queue(poll->head, poll->wait);
                spin_unlock_irq(&ctx->completion_lock);
                return;
        }
        io_poll_remove_req(req);
        io_poll_complete(req, mask, ret);
        spin_unlock_irq(&ctx->completion_lock);

        io_cqring_ev_posted(ctx);

        if (ret < 0 && req->flags & REQ_F_LINK)
                req->flags |= REQ_F_FAIL_LINK;
        io_put_req_find_next(req, &nxt);
        if (nxt)
                *workptr = &nxt->work;
}

static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
                        void *key)
{
        struct io_poll_iocb *poll = wait->private;
        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);

        /*
         * Run completion inline if we can. We're using trylock here because
         * we are violating the completion_lock -> poll wq lock ordering.
         * If we have a link timeout we're going to need the completion_lock
         * for finalizing the request, mark us as having grabbed that already.
         */
        if (mask && spin_trylock_irqsave(&ctx->completion_lock, flags)) {
                io_poll_remove_req(req);
                io_poll_complete(req, mask, 0);
                req->flags |= REQ_F_COMP_LOCKED;
                io_put_req(req);
                spin_unlock_irqrestore(&ctx->completion_lock, flags);

                io_cqring_ev_posted(ctx);
        } else {
                io_queue_async_work(req);
        }

        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 void io_poll_req_insert(struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct rb_node **p = &ctx->cancel_tree.rb_node;
        struct rb_node *parent = NULL;
        struct io_kiocb *tmp;

        while (*p) {
                parent = *p;
                tmp = rb_entry(parent, struct io_kiocb, rb_node);
                if (req->user_data < tmp->user_data)
                        p = &(*p)->rb_left;
                else
                        p = &(*p)->rb_right;
        }
        rb_link_node(&req->rb_node, parent, p);
        rb_insert_color(&req->rb_node, &ctx->cancel_tree);
}

static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe,
                       struct io_kiocb **nxt)
{
        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;

        poll->wait = kmalloc(sizeof(*poll->wait), GFP_KERNEL);
        if (!poll->wait)
                return -ENOMEM;

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

        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);
        poll->wait->private = poll;

        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 */
                        io_poll_req_insert(req);
                spin_unlock(&poll->head->lock);
        }
        if (mask) { /* no async, we'd stolen it */
                ipt.error = 0;
                io_poll_complete(req, mask, 0);
        }
        spin_unlock_irq(&ctx->completion_lock);

        if (mask) {
                io_cqring_ev_posted(ctx);
                io_put_req_find_next(req, nxt);
        }
        return ipt.error;
}

static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer)
{
        struct io_timeout_data *data = container_of(timer,
                                                struct io_timeout_data, timer);
        struct io_kiocb *req = data->req;
        struct io_ring_ctx *ctx = req->ctx;
        unsigned long flags;

        atomic_inc(&ctx->cq_timeouts);

        spin_lock_irqsave(&ctx->completion_lock, flags);
        /*
         * We could be racing with timeout deletion. If the list is empty,
         * then timeout lookup already found it and will be handling it.
         */
        if (!list_empty(&req->list)) {
                struct io_kiocb *prev;

                /*
                 * Adjust the reqs sequence before the current one because it
                 * will consume a slot in the cq_ring and the the cq_tail
                 * pointer will be increased, otherwise other timeout reqs may
                 * return in advance without waiting for enough wait_nr.
                 */
                prev = req;
                list_for_each_entry_continue_reverse(prev, &ctx->timeout_list, list)
                        prev->sequence++;
                list_del_init(&req->list);
        }

        io_cqring_fill_event(req, -ETIME);
        io_commit_cqring(ctx);
        spin_unlock_irqrestore(&ctx->completion_lock, flags);

        io_cqring_ev_posted(ctx);
        if (req->flags & REQ_F_LINK)
                req->flags |= REQ_F_FAIL_LINK;
        io_put_req(req);
        return HRTIMER_NORESTART;
}

static int io_timeout_cancel(struct io_ring_ctx *ctx, __u64 user_data)
{
        struct io_kiocb *req;
        int ret = -ENOENT;

        list_for_each_entry(req, &ctx->timeout_list, list) {
                if (user_data == req->user_data) {
                        list_del_init(&req->list);
                        ret = 0;
                        break;
                }
        }

        if (ret == -ENOENT)
                return ret;

        ret = hrtimer_try_to_cancel(&req->timeout.data->timer);
        if (ret == -1)
                return -EALREADY;

        if (req->flags & REQ_F_LINK)
                req->flags |= REQ_F_FAIL_LINK;
        io_cqring_fill_event(req, -ECANCELED);
        io_put_req(req);
        return 0;
}

/*
 * Remove or update an existing timeout command
 */
static int io_timeout_remove(struct io_kiocb *req,
                             const struct io_uring_sqe *sqe)
{
        struct io_ring_ctx *ctx = req->ctx;
        unsigned flags;
        int ret;

        if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (sqe->flags || sqe->ioprio || sqe->buf_index || sqe->len)
                return -EINVAL;
        flags = READ_ONCE(sqe->timeout_flags);
        if (flags)
                return -EINVAL;

        spin_lock_irq(&ctx->completion_lock);
        ret = io_timeout_cancel(ctx, READ_ONCE(sqe->addr));

        io_cqring_fill_event(req, ret);
        io_commit_cqring(ctx);
        spin_unlock_irq(&ctx->completion_lock);
        io_cqring_ev_posted(ctx);
        if (ret < 0 && req->flags & REQ_F_LINK)
                req->flags |= REQ_F_FAIL_LINK;
        io_put_req(req);
        return 0;
}

static int io_timeout_setup(struct io_kiocb *req)
{
        const struct io_uring_sqe *sqe = req->sqe;
        struct io_timeout_data *data;
        unsigned flags;

        if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
                return -EINVAL;
        if (sqe->ioprio || sqe->buf_index || sqe->len != 1)
                return -EINVAL;
        flags = READ_ONCE(sqe->timeout_flags);
        if (flags & ~IORING_TIMEOUT_ABS)
                return -EINVAL;

        data = kzalloc(sizeof(struct io_timeout_data), GFP_KERNEL);
        if (!data)
                return -ENOMEM;
        data->req = req;
        req->timeout.data = data;
        req->flags |= REQ_F_TIMEOUT;

        if (get_timespec64(&data->ts, u64_to_user_ptr(sqe->addr)))
                return -EFAULT;

        if (flags & IORING_TIMEOUT_ABS)
                data->mode = HRTIMER_MODE_ABS;
        else
                data->mode = HRTIMER_MODE_REL;

        hrtimer_init(&data->timer, CLOCK_MONOTONIC, data->mode);
        return 0;
}

static int io_timeout(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        unsigned count;
        struct io_ring_ctx *ctx = req->ctx;
        struct io_timeout_data *data;
        struct list_head *entry;
        unsigned span = 0;
        int ret;

        ret = io_timeout_setup(req);
        /* common setup allows flags (like links) set, we don't */
        if (!ret && sqe->flags)
                ret = -EINVAL;
        if (ret)
                return ret;

        /*
         * sqe->off holds how many events that need to occur for this
         * timeout event to be satisfied. If it isn't set, then this is
         * a pure timeout request, sequence isn't used.
         */
        count = READ_ONCE(sqe->off);
        if (!count) {
                req->flags |= REQ_F_TIMEOUT_NOSEQ;
                spin_lock_irq(&ctx->completion_lock);
                entry = ctx->timeout_list.prev;
                goto add;
        }

        req->sequence = ctx->cached_sq_head + count - 1;
        req->timeout.data->seq_offset = count;

        /*
         * Insertion sort, ensuring the first entry in the list is always
         * the one we need first.
         */
        spin_lock_irq(&ctx->completion_lock);
        list_for_each_prev(entry, &ctx->timeout_list) {
                struct io_kiocb *nxt = list_entry(entry, struct io_kiocb, list);
                unsigned nxt_sq_head;
                long long tmp, tmp_nxt;
                u32 nxt_offset = nxt->timeout.data->seq_offset;

                if (nxt->flags & REQ_F_TIMEOUT_NOSEQ)
                        continue;

                /*
                 * Since cached_sq_head + count - 1 can overflow, use type long
                 * long to store it.
                 */
                tmp = (long long)ctx->cached_sq_head + count - 1;
                nxt_sq_head = nxt->sequence - nxt_offset + 1;
                tmp_nxt = (long long)nxt_sq_head + nxt_offset - 1;

                /*
                 * cached_sq_head may overflow, and it will never overflow twice
                 * once there is some timeout req still be valid.
                 */
                if (ctx->cached_sq_head < nxt_sq_head)
                        tmp += UINT_MAX;

                if (tmp > tmp_nxt)
                        break;

                /*
                 * Sequence of reqs after the insert one and itself should
                 * be adjusted because each timeout req consumes a slot.
                 */
                span++;
                nxt->sequence++;
        }
        req->sequence -= span;
add:
        list_add(&req->list, entry);
        data = req->timeout.data;
        data->timer.function = io_timeout_fn;
        hrtimer_start(&data->timer, timespec64_to_ktime(data->ts), data->mode);
        spin_unlock_irq(&ctx->completion_lock);
        return 0;
}

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

        return req->user_data == (unsigned long) data;
}

static int io_async_cancel_one(struct io_ring_ctx *ctx, void *sqe_addr)
{
        enum io_wq_cancel cancel_ret;
        int ret = 0;

        cancel_ret = io_wq_cancel_cb(ctx->io_wq, io_cancel_cb, sqe_addr);
        switch (cancel_ret) {
        case IO_WQ_CANCEL_OK:
                ret = 0;
                break;
        case IO_WQ_CANCEL_RUNNING:
                ret = -EALREADY;
                break;
        case IO_WQ_CANCEL_NOTFOUND:
                ret = -ENOENT;
                break;
        }

        return ret;
}

static void io_async_find_and_cancel(struct io_ring_ctx *ctx,
                                     struct io_kiocb *req, __u64 sqe_addr,
                                     struct io_kiocb **nxt, int success_ret)
{
        unsigned long flags;
        int ret;

        ret = io_async_cancel_one(ctx, (void *) (unsigned long) sqe_addr);
        if (ret != -ENOENT) {
                spin_lock_irqsave(&ctx->completion_lock, flags);
                goto done;
        }

        spin_lock_irqsave(&ctx->completion_lock, flags);
        ret = io_timeout_cancel(ctx, sqe_addr);
        if (ret != -ENOENT)
                goto done;
        ret = io_poll_cancel(ctx, sqe_addr);
done:
        if (!ret)
                ret = success_ret;
        io_cqring_fill_event(req, ret);
        io_commit_cqring(ctx);
        spin_unlock_irqrestore(&ctx->completion_lock, flags);
        io_cqring_ev_posted(ctx);

        if (ret < 0 && (req->flags & REQ_F_LINK))
                req->flags |= REQ_F_FAIL_LINK;
        io_put_req_find_next(req, nxt);
}

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

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

        io_async_find_and_cancel(ctx, req, READ_ONCE(sqe->addr), nxt, 0);
        return 0;
}

static int io_req_defer(struct io_kiocb *req)
{
        struct io_uring_sqe *sqe_copy;
        struct io_ring_ctx *ctx = req->ctx;

        /* Still need defer if there is pending req in defer list. */
        if (!req_need_defer(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 (!req_need_defer(req) && list_empty(&ctx->defer_list)) {
                spin_unlock_irq(&ctx->completion_lock);
                kfree(sqe_copy);
                return 0;
        }

        memcpy(sqe_copy, req->sqe, sizeof(*sqe_copy));
        req->flags |= REQ_F_FREE_SQE;
        req->sqe = sqe_copy;

        trace_io_uring_defer(ctx, req, req->user_data);
        list_add_tail(&req->list, &ctx->defer_list);
        spin_unlock_irq(&ctx->completion_lock);
        return -EIOCBQUEUED;
}

__attribute__((nonnull))
static int io_issue_sqe(struct io_kiocb *req, struct io_kiocb **nxt,
                        bool force_nonblock)
{
        int ret, opcode;
        struct io_ring_ctx *ctx = req->ctx;

        opcode = READ_ONCE(req->sqe->opcode);
        switch (opcode) {
        case IORING_OP_NOP:
                ret = io_nop(req);
                break;
        case IORING_OP_READV:
                if (unlikely(req->sqe->buf_index))
                        return -EINVAL;
                ret = io_read(req, nxt, force_nonblock);
                break;
        case IORING_OP_WRITEV:
                if (unlikely(req->sqe->buf_index))
                        return -EINVAL;
                ret = io_write(req, nxt, force_nonblock);
                break;
        case IORING_OP_READ_FIXED:
                ret = io_read(req, nxt, force_nonblock);
                break;
        case IORING_OP_WRITE_FIXED:
                ret = io_write(req, nxt, force_nonblock);
                break;
        case IORING_OP_FSYNC:
                ret = io_fsync(req, req->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_POLL_ADD:
                ret = io_poll_add(req, req->sqe, nxt);
                break;
        case IORING_OP_POLL_REMOVE:
                ret = io_poll_remove(req, req->sqe);
                break;
        case IORING_OP_SYNC_FILE_RANGE:
                ret = io_sync_file_range(req, req->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_SENDMSG:
                ret = io_sendmsg(req, req->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_RECVMSG:
                ret = io_recvmsg(req, req->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_TIMEOUT:
                ret = io_timeout(req, req->sqe);
                break;
        case IORING_OP_TIMEOUT_REMOVE:
                ret = io_timeout_remove(req, req->sqe);
                break;
        case IORING_OP_ACCEPT:
                ret = io_accept(req, req->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_CONNECT:
                ret = io_connect(req, req->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_ASYNC_CANCEL:
                ret = io_async_cancel(req, req->sqe, nxt);
                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 (req->in_async)
                        mutex_lock(&ctx->uring_lock);
                io_iopoll_req_issued(req);
                if (req->in_async)
                        mutex_unlock(&ctx->uring_lock);
        }

        return 0;
}

static void io_link_work_cb(struct io_wq_work **workptr)
{
        struct io_wq_work *work = *workptr;
        struct io_kiocb *link = work->data;

        io_queue_linked_timeout(link);
        work->func = io_wq_submit_work;
}

static void io_wq_submit_work(struct io_wq_work **workptr)
{
        struct io_wq_work *work = *workptr;
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);
        struct io_kiocb *nxt = NULL;
        int ret = 0;

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

        if (work->flags & IO_WQ_WORK_CANCEL)
                ret = -ECANCELED;

        if (!ret) {
                req->has_user = (work->flags & IO_WQ_WORK_HAS_MM) != 0;
                req->in_async = true;
                do {
                        ret = io_issue_sqe(req, &nxt, 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) {
                if (req->flags & REQ_F_LINK)
                        req->flags |= REQ_F_FAIL_LINK;
                io_cqring_add_event(req, ret);
                io_put_req(req);
        }

        /* if a dependent link is ready, pass it back */
        if (!ret && nxt) {
                struct io_kiocb *link;

                io_prep_async_work(nxt, &link);
                *workptr = &nxt->work;
                if (link) {
                        nxt->work.flags |= IO_WQ_WORK_CB;
                        nxt->work.func = io_link_work_cb;
                        nxt->work.data = link;
                }
        }
}

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:
        case IORING_OP_TIMEOUT:
        case IORING_OP_TIMEOUT_REMOVE:
        case IORING_OP_ASYNC_CANCEL:
        case IORING_OP_LINK_TIMEOUT:
                return false;
        default:
                return true;
        }
}

static inline struct file *io_file_from_index(struct io_ring_ctx *ctx,
                                              int index)
{
        struct fixed_file_table *table;

        table = &ctx->file_table[index >> IORING_FILE_TABLE_SHIFT];
        return table->files[index & IORING_FILE_TABLE_MASK];
}

static int io_req_set_file(struct io_submit_state *state, struct io_kiocb *req)
{
        struct io_ring_ctx *ctx = req->ctx;
        unsigned flags;
        int fd;

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

        if (flags & IOSQE_IO_DRAIN)
                req->flags |= REQ_F_IO_DRAIN;

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

        if (flags & IOSQE_FIXED_FILE) {
                if (unlikely(!ctx->file_table ||
                    (unsigned) fd >= ctx->nr_user_files))
                        return -EBADF;
                fd = array_index_nospec(fd, ctx->nr_user_files);
                req->file = io_file_from_index(ctx, fd);
                if (!req->file)
                        return -EBADF;
                req->flags |= REQ_F_FIXED_FILE;
        } else {
                if (req->needs_fixed_file)
                        return -EBADF;
                trace_io_uring_file_get(ctx, fd);
                req->file = io_file_get(state, fd);
                if (unlikely(!req->file))
                        return -EBADF;
        }

        return 0;
}

static int io_grab_files(struct io_kiocb *req)
{
        int ret = -EBADF;
        struct io_ring_ctx *ctx = req->ctx;

        rcu_read_lock();
        spin_lock_irq(&ctx->inflight_lock);
        /*
         * We use the f_ops->flush() handler to ensure that we can flush
         * out work accessing these files if the fd is closed. Check if
         * the fd has changed since we started down this path, and disallow
         * this operation if it has.
         */
        if (fcheck(req->ring_fd) == req->ring_file) {
                list_add(&req->inflight_entry, &ctx->inflight_list);
                req->flags |= REQ_F_INFLIGHT;
                req->work.files = current->files;
                ret = 0;
        }
        spin_unlock_irq(&ctx->inflight_lock);
        rcu_read_unlock();

        return ret;
}

static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer)
{
        struct io_timeout_data *data = container_of(timer,
                                                struct io_timeout_data, timer);
        struct io_kiocb *req = data->req;
        struct io_ring_ctx *ctx = req->ctx;
        struct io_kiocb *prev = NULL;
        unsigned long flags;

        spin_lock_irqsave(&ctx->completion_lock, flags);

        /*
         * We don't expect the list to be empty, that will only happen if we
         * race with the completion of the linked work.
         */
        if (!list_empty(&req->list)) {
                prev = list_entry(req->list.prev, struct io_kiocb, link_list);
                if (refcount_inc_not_zero(&prev->refs)) {
                        list_del_init(&req->list);
                        prev->flags &= ~REQ_F_LINK_TIMEOUT;
                } else
                        prev = NULL;
        }

        spin_unlock_irqrestore(&ctx->completion_lock, flags);

        if (prev) {
                if (prev->flags & REQ_F_LINK)
                        prev->flags |= REQ_F_FAIL_LINK;
                io_async_find_and_cancel(ctx, req, prev->user_data, NULL,
                                                -ETIME);
                io_put_req(prev);
        } else {
                io_cqring_add_event(req, -ETIME);
                io_put_req(req);
        }
        return HRTIMER_NORESTART;
}

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

        /*
         * If the list is now empty, then our linked request finished before
         * we got a chance to setup the timer
         */
        spin_lock_irq(&ctx->completion_lock);
        if (!list_empty(&req->list)) {
                struct io_timeout_data *data = req->timeout.data;

                data->timer.function = io_link_timeout_fn;
                hrtimer_start(&data->timer, timespec64_to_ktime(data->ts),
                                data->mode);
        }
        spin_unlock_irq(&ctx->completion_lock);

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

static struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req)
{
        struct io_kiocb *nxt;

        if (!(req->flags & REQ_F_LINK))
                return NULL;

        nxt = list_first_entry_or_null(&req->link_list, struct io_kiocb, list);
        if (!nxt || nxt->sqe->opcode != IORING_OP_LINK_TIMEOUT)
                return NULL;

        req->flags |= REQ_F_LINK_TIMEOUT;
        return nxt;
}

static void __io_queue_sqe(struct io_kiocb *req)
{
        struct io_kiocb *linked_timeout = io_prep_linked_timeout(req);
        struct io_kiocb *nxt = NULL;
        int ret;

        ret = io_issue_sqe(req, &nxt, true);
        if (nxt)
                io_queue_async_work(nxt);

        /*
         * We async punt it if the file wasn't marked NOWAIT, or if the file
         * doesn't support non-blocking read/write attempts
         */
        if (ret == -EAGAIN && (!(req->flags & REQ_F_NOWAIT) ||
            (req->flags & REQ_F_MUST_PUNT))) {
                struct io_uring_sqe *sqe_copy;

                sqe_copy = kmemdup(req->sqe, sizeof(*sqe_copy), GFP_KERNEL);
                if (!sqe_copy)
                        goto err;

                req->sqe = sqe_copy;
                req->flags |= REQ_F_FREE_SQE;

                if (req->work.flags & IO_WQ_WORK_NEEDS_FILES) {
                        ret = io_grab_files(req);
                        if (ret)
                                goto err;
                }

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

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

        if (linked_timeout) {
                if (!ret)
                        io_queue_linked_timeout(linked_timeout);
                else
                        io_put_req(linked_timeout);
        }

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

static void io_queue_sqe(struct io_kiocb *req)
{
        int ret;

        if (unlikely(req->ctx->drain_next)) {
                req->flags |= REQ_F_IO_DRAIN;
                req->ctx->drain_next = false;
        }
        req->ctx->drain_next = (req->flags & REQ_F_DRAIN_LINK);

        ret = io_req_defer(req);
        if (ret) {
                if (ret != -EIOCBQUEUED) {
                        io_cqring_add_event(req, ret);
                        if (req->flags & REQ_F_LINK)
                                req->flags |= REQ_F_FAIL_LINK;
                        io_double_put_req(req);
                }
        } else
                __io_queue_sqe(req);
}

static inline void io_queue_link_head(struct io_kiocb *req)
{
        if (unlikely(req->flags & REQ_F_FAIL_LINK)) {
                io_cqring_add_event(req, -ECANCELED);
                io_double_put_req(req);
        } else
                io_queue_sqe(req);
}


#define SQE_VALID_FLAGS (IOSQE_FIXED_FILE|IOSQE_IO_DRAIN|IOSQE_IO_LINK)

static void io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state,
                          struct io_kiocb **link)
{
        struct io_ring_ctx *ctx = req->ctx;
        int ret;

        req->user_data = req->sqe->user_data;

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

        ret = io_req_set_file(state, req);
        if (unlikely(ret)) {
err_req:
                io_cqring_add_event(req, ret);
                io_double_put_req(req);
                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;
                struct io_uring_sqe *sqe_copy;

                if (req->sqe->flags & IOSQE_IO_DRAIN)
                        (*link)->flags |= REQ_F_DRAIN_LINK | REQ_F_IO_DRAIN;

                if (READ_ONCE(req->sqe->opcode) == IORING_OP_LINK_TIMEOUT) {
                        ret = io_timeout_setup(req);
                        /* common setup allows offset being set, we don't */
                        if (!ret && req->sqe->off)
                                ret = -EINVAL;
                        if (ret) {
                                prev->flags |= REQ_F_FAIL_LINK;
                                goto err_req;
                        }
                }

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

                req->sqe = sqe_copy;
                req->flags |= REQ_F_FREE_SQE;
                trace_io_uring_link(ctx, req, prev);
                list_add_tail(&req->list, &prev->link_list);
        } else if (req->sqe->flags & IOSQE_IO_LINK) {
                req->flags |= REQ_F_LINK;

                INIT_LIST_HEAD(&req->link_list);
                *link = req;
        } else {
                io_queue_sqe(req);
        }
}

/*
 * 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_rings *rings = ctx->rings;

        if (ctx->cached_sq_head != READ_ONCE(rings->sq.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(&rings->sq.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 io_kiocb *req)
{
        struct io_rings *rings = ctx->rings;
        u32 *sq_array = ctx->sq_array;
        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 (unlikely(head == smp_load_acquire(&rings->sq.tail)))
                return false;

        head = READ_ONCE(sq_array[head & ctx->sq_mask]);
        if (likely(head < ctx->sq_entries)) {
                /*
                 * All io need record the previous position, if LINK vs DARIN,
                 * it can be used to mark the position of the first IO in the
                 * link list.
                 */
                req->sequence = ctx->cached_sq_head;
                req->sqe = &ctx->sq_sqes[head];
                ctx->cached_sq_head++;
                return true;
        }

        /* drop invalid entries */
        ctx->cached_sq_head++;
        ctx->cached_sq_dropped++;
        WRITE_ONCE(rings->sq_dropped, ctx->cached_sq_dropped);
        return false;
}

static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
                          struct file *ring_file, int ring_fd,
                          struct mm_struct **mm, bool async)
{
        struct io_submit_state state, *statep = NULL;
        struct io_kiocb *link = NULL;
        int i, submitted = 0;
        bool mm_fault = false;

        /* if we have a backlog and couldn't flush it all, return BUSY */
        if (!list_empty(&ctx->cq_overflow_list) &&
            !io_cqring_overflow_flush(ctx, false))
                return -EBUSY;

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

        for (i = 0; i < nr; i++) {
                struct io_kiocb *req;
                unsigned int sqe_flags;

                req = io_get_req(ctx, statep);
                if (unlikely(!req)) {
                        if (!submitted)
                                submitted = -EAGAIN;
                        break;
                }
                if (!io_get_sqring(ctx, req)) {
                        __io_free_req(req);
                        break;
                }

                if (io_sqe_needs_user(req->sqe) && !*mm) {
                        mm_fault = mm_fault || !mmget_not_zero(ctx->sqo_mm);
                        if (!mm_fault) {
                                use_mm(ctx->sqo_mm);
                                *mm = ctx->sqo_mm;
                        }
                }

                sqe_flags = req->sqe->flags;

                req->ring_file = ring_file;
                req->ring_fd = ring_fd;
                req->has_user = *mm != NULL;
                req->in_async = async;
                req->needs_fixed_file = async;
                trace_io_uring_submit_sqe(ctx, req->sqe->user_data,
                                          true, async);
                io_submit_sqe(req, statep, &link);
                submitted++;

                /*
                 * If previous wasn't linked and we have a linked command,
                 * that's the end of the chain. Submit the previous link.
                 */
                if (!(sqe_flags & IOSQE_IO_LINK) && link) {
                        io_queue_link_head(link);
                        link = NULL;
                }
        }

        if (link)
                io_queue_link_head(link);
        if (statep)
                io_submit_state_end(&state);

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

        return submitted;
}

static int io_sq_thread(void *data)
{
        struct io_ring_ctx *ctx = data;
        struct mm_struct *cur_mm = NULL;
        const struct cred *old_cred;
        mm_segment_t old_fs;
        DEFINE_WAIT(wait);
        unsigned inflight;
        unsigned long timeout;
        int ret;

        complete(&ctx->completions[1]);

        old_fs = get_fs();
        set_fs(USER_DS);
        old_cred = override_creds(ctx->creds);

        ret = timeout = inflight = 0;
        while (!kthread_should_park()) {
                unsigned int to_submit;

                if (inflight) {
                        unsigned nr_events = 0;

                        if (ctx->flags & IORING_SETUP_IOPOLL) {
                                /*
                                 * inflight is the count of the maximum possible
                                 * entries we submitted, but it can be smaller
                                 * if we dropped some of them. If we don't have
                                 * poll entries available, then we know that we
                                 * have nothing left to poll for. Reset the
                                 * inflight count to zero in that case.
                                 */
                                mutex_lock(&ctx->uring_lock);
                                if (!list_empty(&ctx->poll_list))
                                        __io_iopoll_check(ctx, &nr_events, 0);
                                else
                                        inflight = 0;
                                mutex_unlock(&ctx->uring_lock);
                        } 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;
                }

                to_submit = io_sqring_entries(ctx);

                /*
                 * If submit got -EBUSY, flag us as needing the application
                 * to enter the kernel to reap and flush events.
                 */
                if (!to_submit || ret == -EBUSY) {
                        /*
                         * We're polling. If we're within the defined idle
                         * period, then let us spin without work before going
                         * to sleep. The exception is if we got EBUSY doing
                         * more IO, we should wait for the application to
                         * reap events and wake us up.
                         */
                        if (inflight ||
                            (!time_after(jiffies, timeout) && ret != -EBUSY)) {
                                cond_resched();
                                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->rings->sq_flags |= IORING_SQ_NEED_WAKEUP;
                        /* make sure to read SQ tail after writing flags */
                        smp_mb();

                        to_submit = io_sqring_entries(ctx);
                        if (!to_submit || ret == -EBUSY) {
                                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->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
                                continue;
                        }
                        finish_wait(&ctx->sqo_wait, &wait);

                        ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
                }

                to_submit = min(to_submit, ctx->sq_entries);
                ret = io_submit_sqes(ctx, to_submit, NULL, -1, &cur_mm, true);
                if (ret > 0)
                        inflight += ret;
        }

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

        kthread_parkme();

        return 0;
}

struct io_wait_queue {
        struct wait_queue_entry wq;
        struct io_ring_ctx *ctx;
        unsigned to_wait;
        unsigned nr_timeouts;
};

static inline bool io_should_wake(struct io_wait_queue *iowq, bool noflush)
{
        struct io_ring_ctx *ctx = iowq->ctx;

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

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

        /* use noflush == true, as we can't safely rely on locking context */
        if (!io_should_wake(iowq, true))
                return -1;

        return autoremove_wake_function(curr, mode, wake_flags, key);
}

/*
 * 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_wait_queue iowq = {
                .wq = {
                        .private        = current,
                        .func           = io_wake_function,
                        .entry          = LIST_HEAD_INIT(iowq.wq.entry),
                },
                .ctx            = ctx,
                .to_wait        = min_events,
        };
        struct io_rings *rings = ctx->rings;
        int ret = 0;

        if (io_cqring_events(ctx, false) >= 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;
        }

        iowq.nr_timeouts = atomic_read(&ctx->cq_timeouts);
        trace_io_uring_cqring_wait(ctx, min_events);
        do {
                prepare_to_wait_exclusive(&ctx->wait, &iowq.wq,
                                                TASK_INTERRUPTIBLE);
                if (io_should_wake(&iowq, false))
                        break;
                schedule();
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
        } while (1);
        finish_wait(&ctx->wait, &iowq.wq);

        restore_saved_sigmask_unless(ret == -EINTR);

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

static void __io_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++) {
                struct file *file;

                file = io_file_from_index(ctx, i);
                if (file)
                        fput(file);
        }
#endif
}

static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
{
        unsigned nr_tables, i;

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

        __io_sqe_files_unregister(ctx);
        nr_tables = DIV_ROUND_UP(ctx->nr_user_files, IORING_MAX_FILES_TABLE);
        for (i = 0; i < nr_tables; i++)
                kfree(ctx->file_table[i].files);
        kfree(ctx->file_table);
        ctx->file_table = 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->completions[1]);
                /*
                 * 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->io_wq) {
                io_wq_destroy(ctx->io_wq);
                ctx->io_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;

        if (ctx->io_wq)
                io_wq_flush(ctx->io_wq);

        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, nr_files;

        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;

        nr_files = 0;
        fpl->user = get_uid(ctx->user);
        for (i = 0; i < nr; i++) {
                struct file *file = io_file_from_index(ctx, i + offset);

                if (!file)
                        continue;
                fpl->fp[nr_files] = get_file(file);
                unix_inflight(fpl->user, fpl->fp[nr_files]);
                nr_files++;
        }

        if (nr_files) {
                fpl->max = SCM_MAX_FD;
                fpl->count = nr_files;
                UNIXCB(skb).fp = fpl;
                skb->destructor = io_destruct_skb;
                refcount_add(skb->truesize, &sk->sk_wmem_alloc);
                skb_queue_head(&sk->sk_receive_queue, skb);

                for (i = 0; i < nr_files; i++)
                        fput(fpl->fp[i]);
        } else {
                kfree_skb(skb);
                kfree(fpl);
        }

        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) {
                struct file *file = io_file_from_index(ctx, total);

                if (file)
                        fput(file);
                total++;
        }

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

static int io_sqe_alloc_file_tables(struct io_ring_ctx *ctx, unsigned nr_tables,
                                    unsigned nr_files)
{
        int i;

        for (i = 0; i < nr_tables; i++) {
                struct fixed_file_table *table = &ctx->file_table[i];
                unsigned this_files;

                this_files = min(nr_files, IORING_MAX_FILES_TABLE);
                table->files = kcalloc(this_files, sizeof(struct file *),
                                        GFP_KERNEL);
                if (!table->files)
                        break;
                nr_files -= this_files;
        }

        if (i == nr_tables)
                return 0;

        for (i = 0; i < nr_tables; i++) {
                struct fixed_file_table *table = &ctx->file_table[i];
                kfree(table->files);
        }
        return 1;
}

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

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

        nr_tables = DIV_ROUND_UP(nr_args, IORING_MAX_FILES_TABLE);
        ctx->file_table = kcalloc(nr_tables, sizeof(struct fixed_file_table),
                                        GFP_KERNEL);
        if (!ctx->file_table)
                return -ENOMEM;

        if (io_sqe_alloc_file_tables(ctx, nr_tables, nr_args)) {
                kfree(ctx->file_table);
                ctx->file_table = NULL;
                return -ENOMEM;
        }

        for (i = 0; i < nr_args; i++, ctx->nr_user_files++) {
                struct fixed_file_table *table;
                unsigned index;

                ret = -EFAULT;
                if (copy_from_user(&fd, &fds[i], sizeof(fd)))
                        break;
                /* allow sparse sets */
                if (fd == -1) {
                        ret = 0;
                        continue;
                }

                table = &ctx->file_table[i >> IORING_FILE_TABLE_SHIFT];
                index = i & IORING_FILE_TABLE_MASK;
                table->files[index] = fget(fd);

                ret = -EBADF;
                if (!table->files[index])
                        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 (table->files[index]->f_op == &io_uring_fops) {
                        fput(table->files[index]);
                        break;
                }
                ret = 0;
        }

        if (ret) {
                for (i = 0; i < ctx->nr_user_files; i++) {
                        struct file *file;

                        file = io_file_from_index(ctx, i);
                        if (file)
                                fput(file);
                }
                for (i = 0; i < nr_tables; i++)
                        kfree(ctx->file_table[i].files);

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

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

        return ret;
}

static void io_sqe_file_unregister(struct io_ring_ctx *ctx, int index)
{
#if defined(CONFIG_UNIX)
        struct file *file = io_file_from_index(ctx, index);
        struct sock *sock = ctx->ring_sock->sk;
        struct sk_buff_head list, *head = &sock->sk_receive_queue;
        struct sk_buff *skb;
        int i;

        __skb_queue_head_init(&list);

        /*
         * Find the skb that holds this file in its SCM_RIGHTS. When found,
         * remove this entry and rearrange the file array.
         */
        skb = skb_dequeue(head);
        while (skb) {
                struct scm_fp_list *fp;

                fp = UNIXCB(skb).fp;
                for (i = 0; i < fp->count; i++) {
                        int left;

                        if (fp->fp[i] != file)
                                continue;

                        unix_notinflight(fp->user, fp->fp[i]);
                        left = fp->count - 1 - i;
                        if (left) {
                                memmove(&fp->fp[i], &fp->fp[i + 1],
                                                left * sizeof(struct file *));
                        }
                        fp->count--;
                        if (!fp->count) {
                                kfree_skb(skb);
                                skb = NULL;
                        } else {
                                __skb_queue_tail(&list, skb);
                        }
                        fput(file);
                        file = NULL;
                        break;
                }

                if (!file)
                        break;

                __skb_queue_tail(&list, skb);

                skb = skb_dequeue(head);
        }

        if (skb_peek(&list)) {
                spin_lock_irq(&head->lock);
                while ((skb = __skb_dequeue(&list)) != NULL)
                        __skb_queue_tail(head, skb);
                spin_unlock_irq(&head->lock);
        }
#else
        fput(io_file_from_index(ctx, index));
#endif
}

static int io_sqe_file_register(struct io_ring_ctx *ctx, struct file *file,
                                int index)
{
#if defined(CONFIG_UNIX)
        struct sock *sock = ctx->ring_sock->sk;
        struct sk_buff_head *head = &sock->sk_receive_queue;
        struct sk_buff *skb;

        /*
         * See if we can merge this file into an existing skb SCM_RIGHTS
         * file set. If there's no room, fall back to allocating a new skb
         * and filling it in.
         */
        spin_lock_irq(&head->lock);
        skb = skb_peek(head);
        if (skb) {
                struct scm_fp_list *fpl = UNIXCB(skb).fp;

                if (fpl->count < SCM_MAX_FD) {
                        __skb_unlink(skb, head);
                        spin_unlock_irq(&head->lock);
                        fpl->fp[fpl->count] = get_file(file);
                        unix_inflight(fpl->user, fpl->fp[fpl->count]);
                        fpl->count++;
                        spin_lock_irq(&head->lock);
                        __skb_queue_head(head, skb);
                } else {
                        skb = NULL;
                }
        }
        spin_unlock_irq(&head->lock);

        if (skb) {
                fput(file);
                return 0;
        }

        return __io_sqe_files_scm(ctx, 1, index);
#else
        return 0;
#endif
}

static int io_sqe_files_update(struct io_ring_ctx *ctx, void __user *arg,
                               unsigned nr_args)
{
        struct io_uring_files_update up;
        __s32 __user *fds;
        int fd, i, err;
        __u32 done;

        if (!ctx->file_table)
                return -ENXIO;
        if (!nr_args)
                return -EINVAL;
        if (copy_from_user(&up, arg, sizeof(up)))
                return -EFAULT;
        if (check_add_overflow(up.offset, nr_args, &done))
                return -EOVERFLOW;
        if (done > ctx->nr_user_files)
                return -EINVAL;

        done = 0;
        fds = (__s32 __user *) up.fds;
        while (nr_args) {
                struct fixed_file_table *table;
                unsigned index;

                err = 0;
                if (copy_from_user(&fd, &fds[done], sizeof(fd))) {
                        err = -EFAULT;
                        break;
                }
                i = array_index_nospec(up.offset, ctx->nr_user_files);
                table = &ctx->file_table[i >> IORING_FILE_TABLE_SHIFT];
                index = i & IORING_FILE_TABLE_MASK;
                if (table->files[index]) {
                        io_sqe_file_unregister(ctx, i);
                        table->files[index] = NULL;
                }
                if (fd != -1) {
                        struct file *file;

                        file = fget(fd);
                        if (!file) {
                                err = -EBADF;
                                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 (file->f_op == &io_uring_fops) {
                                fput(file);
                                err = -EBADF;
                                break;
                        }
                        table->files[index] = file;
                        err = io_sqe_file_register(ctx, file, i);
                        if (err)
                                break;
                }
                nr_args--;
                done++;
                up.offset++;
        }

        return done ? done : err;
}

static void io_put_work(struct io_wq_work *work)
{
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);

        io_put_req(req);
}

static void io_get_work(struct io_wq_work *work)
{
        struct io_kiocb *req = container_of(work, struct io_kiocb, work);

        refcount_inc(&req->refs);
}

static int io_sq_offload_start(struct io_ring_ctx *ctx,
                               struct io_uring_params *p)
{
        struct io_wq_data data;
        unsigned concurrency;
        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;
        }

        data.mm = ctx->sqo_mm;
        data.user = ctx->user;
        data.creds = ctx->creds;
        data.get_work = io_get_work;
        data.put_work = io_put_work;

        /* Do QD, or 4 * CPUS, whatever is smallest */
        concurrency = min(ctx->sq_entries, 4 * num_online_cpus());
        ctx->io_wq = io_wq_create(concurrency, &data);
        if (IS_ERR(ctx->io_wq)) {
                ret = PTR_ERR(ctx->io_wq);
                ctx->io_wq = NULL;
                goto err;
        }

        return 0;
err:
        io_finish_async(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 rings_size(unsigned sq_entries, unsigned cq_entries,
                                size_t *sq_offset)
{
        struct io_rings *rings;
        size_t off, sq_array_size;

        off = struct_size(rings, cqes, cq_entries);
        if (off == SIZE_MAX)
                return SIZE_MAX;

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

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

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

        if (sq_offset)
                *sq_offset = off;

        return off;
}

static unsigned long ring_pages(unsigned sq_entries, unsigned cq_entries)
{
        size_t pages;

        pages = (size_t)1 << get_order(
                rings_size(sq_entries, cq_entries, NULL));
        pages += (size_t)1 << get_order(
                array_size(sizeof(struct io_uring_sqe), sq_entries));

        return pages;
}

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_user_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)
                                put_user_pages(pages, pret);
                        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->rings);
        io_mem_free(ctx->sq_sqes);

        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);
        put_cred(ctx->creds);
        kfree(ctx->completions);
        kmem_cache_free(req_cachep, ctx->fallback_req);
        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->rings->sq.tail) - ctx->cached_sq_head !=
            ctx->rings->sq_ring_entries)
                mask |= EPOLLOUT | EPOLLWRNORM;
        if (READ_ONCE(ctx->rings->cq.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_kill_timeouts(ctx);
        io_poll_remove_all(ctx);

        if (ctx->io_wq)
                io_wq_cancel_all(ctx->io_wq);

        io_iopoll_reap_events(ctx);
        /* if we failed setting up the ctx, we might not have any rings */
        if (ctx->rings)
                io_cqring_overflow_flush(ctx, true);
        wait_for_completion(&ctx->completions[0]);
        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 void io_uring_cancel_files(struct io_ring_ctx *ctx,
                                  struct files_struct *files)
{
        struct io_kiocb *req;
        DEFINE_WAIT(wait);

        while (!list_empty_careful(&ctx->inflight_list)) {
                struct io_kiocb *cancel_req = NULL;

                spin_lock_irq(&ctx->inflight_lock);
                list_for_each_entry(req, &ctx->inflight_list, inflight_entry) {
                        if (req->work.files != files)
                                continue;
                        /* req is being completed, ignore */
                        if (!refcount_inc_not_zero(&req->refs))
                                continue;
                        cancel_req = req;
                        break;
                }
                if (cancel_req)
                        prepare_to_wait(&ctx->inflight_wait, &wait,
                                                TASK_UNINTERRUPTIBLE);
                spin_unlock_irq(&ctx->inflight_lock);

                /* We need to keep going until we don't find a matching req */
                if (!cancel_req)
                        break;

                io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
                io_put_req(cancel_req);
                schedule();
        }
        finish_wait(&ctx->inflight_wait, &wait);
}

static int io_uring_flush(struct file *file, void *data)
{
        struct io_ring_ctx *ctx = file->private_data;

        io_uring_cancel_files(ctx, data);
        if (fatal_signal_pending(current) || (current->flags & PF_EXITING)) {
                io_cqring_overflow_flush(ctx, true);
                io_wq_cancel_all(ctx->io_wq);
        }
        return 0;
}

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

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

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

        return ptr;
}

#ifdef CONFIG_MMU

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

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

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

#else /* !CONFIG_MMU */

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

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

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

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

        return (unsigned long) ptr;
}

#endif /* !CONFIG_MMU */

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.
         */
        ret = 0;
        if (ctx->flags & IORING_SETUP_SQPOLL) {
                if (!list_empty_careful(&ctx->cq_overflow_list))
                        io_cqring_overflow_flush(ctx, false);
                if (flags & IORING_ENTER_SQ_WAKEUP)
                        wake_up(&ctx->sqo_wait);
                submitted = to_submit;
        } else if (to_submit) {
                struct mm_struct *cur_mm;

                to_submit = min(to_submit, ctx->sq_entries);
                mutex_lock(&ctx->uring_lock);
                /* already have mm, so io_submit_sqes() won't try to grab it */
                cur_mm = ctx->sqo_mm;
                submitted = io_submit_sqes(ctx, to_submit, f.file, fd,
                                           &cur_mm, false);
                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);
                }
        }

        percpu_ref_put(&ctx->refs);
out_fput:
        fdput(f);
        return submitted ? submitted : ret;
}

static const struct file_operations io_uring_fops = {
        .release        = io_uring_release,
        .flush          = io_uring_flush,
        .mmap           = io_uring_mmap,
#ifndef CONFIG_MMU
        .get_unmapped_area = io_uring_nommu_get_unmapped_area,
        .mmap_capabilities = io_uring_nommu_mmap_capabilities,
#endif
        .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_rings *rings;
        size_t size, sq_array_offset;

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

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

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

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

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

        return 0;
}

/*
 * 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. If the application has
         * set IORING_SETUP_CQSIZE, it will have passed in the desired number
         * of CQ ring entries manually.
         */
        p->sq_entries = roundup_pow_of_two(entries);
        if (p->flags & IORING_SETUP_CQSIZE) {
                /*
                 * If IORING_SETUP_CQSIZE is set, we do the same roundup
                 * to a power-of-two, if it isn't already. We do NOT impose
                 * any cq vs sq ring sizing.
                 */
                if (p->cq_entries < p->sq_entries || p->cq_entries > IORING_MAX_CQ_ENTRIES)
                        return -EINVAL;
                p->cq_entries = roundup_pow_of_two(p->cq_entries);
        } else {
                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;
        ctx->creds = prepare_creds();

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

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

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

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

        /*
         * Install ring fd as the very last thing, so we don't risk someone
         * having closed it before we finish setup
         */
        ret = io_uring_get_fd(ctx);
        if (ret < 0)
                goto err;

        p->features = IORING_FEAT_SINGLE_MMAP | IORING_FEAT_NODROP;
        trace_io_uring_create(ret, ctx, p->sq_entries, p->cq_entries, p->flags);
        return ret;
err:
        io_ring_ctx_wait_and_kill(ctx);
        return ret;
}

/*
 * Sets up an aio uring context, and returns the fd. Applications asks for a
 * ring size, we return the actual sq/cq ring sizes (among other things) in the
 * params structure passed in.
 */
static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
{
        struct io_uring_params p;
        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 | IORING_SETUP_CQSIZE))
                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->completions[0]);
        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_FILES_UPDATE:
                ret = io_sqe_files_update(ctx, arg, nr_args);
                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->completions[0]);
        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);
        trace_io_uring_register(ctx, opcode, ctx->nr_user_files, ctx->nr_user_bufs,
                                                        ctx->cq_ev_fd != NULL, ret);
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);