KVM: Harden copying of userspace-array against overflow

[thirdparty/kernel/stable.git] / io_uring / poll.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/hashtable.h>
#include <linux/io_uring.h>

#include <trace/events/io_uring.h>

#include <uapi/linux/io_uring.h>

#include "io_uring.h"
#include "refs.h"
#include "opdef.h"
#include "kbuf.h"
#include "poll.h"
#include "cancel.h"

struct io_poll_update {
        struct file                     *file;
        u64                             old_user_data;
        u64                             new_user_data;
        __poll_t                        events;
        bool                            update_events;
        bool                            update_user_data;
};

struct io_poll_table {
        struct poll_table_struct pt;
        struct io_kiocb *req;
        int nr_entries;
        int error;
        bool owning;
        /* output value, set only if arm poll returns >0 */
        __poll_t result_mask;
};

#define IO_POLL_CANCEL_FLAG     BIT(31)
#define IO_POLL_RETRY_FLAG      BIT(30)
#define IO_POLL_REF_MASK        GENMASK(29, 0)

/*
 * We usually have 1-2 refs taken, 128 is more than enough and we want to
 * maximise the margin between this amount and the moment when it overflows.
 */
#define IO_POLL_REF_BIAS        128

#define IO_WQE_F_DOUBLE         1

static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
                        void *key);

static inline struct io_kiocb *wqe_to_req(struct wait_queue_entry *wqe)
{
        unsigned long priv = (unsigned long)wqe->private;

        return (struct io_kiocb *)(priv & ~IO_WQE_F_DOUBLE);
}

static inline bool wqe_is_double(struct wait_queue_entry *wqe)
{
        unsigned long priv = (unsigned long)wqe->private;

        return priv & IO_WQE_F_DOUBLE;
}

static bool io_poll_get_ownership_slowpath(struct io_kiocb *req)
{
        int v;

        /*
         * poll_refs are already elevated and we don't have much hope for
         * grabbing the ownership. Instead of incrementing set a retry flag
         * to notify the loop that there might have been some change.
         */
        v = atomic_fetch_or(IO_POLL_RETRY_FLAG, &req->poll_refs);
        if (v & IO_POLL_REF_MASK)
                return false;
        return !(atomic_fetch_inc(&req->poll_refs) & IO_POLL_REF_MASK);
}

/*
 * If refs part of ->poll_refs (see IO_POLL_REF_MASK) is 0, it's free. We can
 * bump it and acquire ownership. It's disallowed to modify requests while not
 * owning it, that prevents from races for enqueueing task_work's and b/w
 * arming poll and wakeups.
 */
static inline bool io_poll_get_ownership(struct io_kiocb *req)
{
        if (unlikely(atomic_read(&req->poll_refs) >= IO_POLL_REF_BIAS))
                return io_poll_get_ownership_slowpath(req);
        return !(atomic_fetch_inc(&req->poll_refs) & IO_POLL_REF_MASK);
}

static void io_poll_mark_cancelled(struct io_kiocb *req)
{
        atomic_or(IO_POLL_CANCEL_FLAG, &req->poll_refs);
}

static struct io_poll *io_poll_get_double(struct io_kiocb *req)
{
        /* pure poll stashes this in ->async_data, poll driven retry elsewhere */
        if (req->opcode == IORING_OP_POLL_ADD)
                return req->async_data;
        return req->apoll->double_poll;
}

static struct io_poll *io_poll_get_single(struct io_kiocb *req)
{
        if (req->opcode == IORING_OP_POLL_ADD)
                return io_kiocb_to_cmd(req, struct io_poll);
        return &req->apoll->poll;
}

static void io_poll_req_insert(struct io_kiocb *req)
{
        struct io_hash_table *table = &req->ctx->cancel_table;
        u32 index = hash_long(req->cqe.user_data, table->hash_bits);
        struct io_hash_bucket *hb = &table->hbs[index];

        spin_lock(&hb->lock);
        hlist_add_head(&req->hash_node, &hb->list);
        spin_unlock(&hb->lock);
}

static void io_poll_req_delete(struct io_kiocb *req, struct io_ring_ctx *ctx)
{
        struct io_hash_table *table = &req->ctx->cancel_table;
        u32 index = hash_long(req->cqe.user_data, table->hash_bits);
        spinlock_t *lock = &table->hbs[index].lock;

        spin_lock(lock);
        hash_del(&req->hash_node);
        spin_unlock(lock);
}

static void io_poll_req_insert_locked(struct io_kiocb *req)
{
        struct io_hash_table *table = &req->ctx->cancel_table_locked;
        u32 index = hash_long(req->cqe.user_data, table->hash_bits);

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

        hlist_add_head(&req->hash_node, &table->hbs[index].list);
}

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

        if (req->flags & REQ_F_HASH_LOCKED) {
                /*
                 * ->cancel_table_locked is protected by ->uring_lock in
                 * contrast to per bucket spinlocks. Likely, tctx_task_work()
                 * already grabbed the mutex for us, but there is a chance it
                 * failed.
                 */
                io_tw_lock(ctx, ts);
                hash_del(&req->hash_node);
                req->flags &= ~REQ_F_HASH_LOCKED;
        } else {
                io_poll_req_delete(req, ctx);
        }
}

static void io_init_poll_iocb(struct io_poll *poll, __poll_t events)
{
        poll->head = NULL;
#define IO_POLL_UNMASK  (EPOLLERR|EPOLLHUP|EPOLLNVAL|EPOLLRDHUP)
        /* mask in events that we always want/need */
        poll->events = events | IO_POLL_UNMASK;
        INIT_LIST_HEAD(&poll->wait.entry);
        init_waitqueue_func_entry(&poll->wait, io_poll_wake);
}

static inline void io_poll_remove_entry(struct io_poll *poll)
{
        struct wait_queue_head *head = smp_load_acquire(&poll->head);

        if (head) {
                spin_lock_irq(&head->lock);
                list_del_init(&poll->wait.entry);
                poll->head = NULL;
                spin_unlock_irq(&head->lock);
        }
}

static void io_poll_remove_entries(struct io_kiocb *req)
{
        /*
         * Nothing to do if neither of those flags are set. Avoid dipping
         * into the poll/apoll/double cachelines if we can.
         */
        if (!(req->flags & (REQ_F_SINGLE_POLL | REQ_F_DOUBLE_POLL)))
                return;

        /*
         * While we hold the waitqueue lock and the waitqueue is nonempty,
         * wake_up_pollfree() will wait for us.  However, taking the waitqueue
         * lock in the first place can race with the waitqueue being freed.
         *
         * We solve this as eventpoll does: by taking advantage of the fact that
         * all users of wake_up_pollfree() will RCU-delay the actual free.  If
         * we enter rcu_read_lock() and see that the pointer to the queue is
         * non-NULL, we can then lock it without the memory being freed out from
         * under us.
         *
         * Keep holding rcu_read_lock() as long as we hold the queue lock, in
         * case the caller deletes the entry from the queue, leaving it empty.
         * In that case, only RCU prevents the queue memory from being freed.
         */
        rcu_read_lock();
        if (req->flags & REQ_F_SINGLE_POLL)
                io_poll_remove_entry(io_poll_get_single(req));
        if (req->flags & REQ_F_DOUBLE_POLL)
                io_poll_remove_entry(io_poll_get_double(req));
        rcu_read_unlock();
}

enum {
        IOU_POLL_DONE = 0,
        IOU_POLL_NO_ACTION = 1,
        IOU_POLL_REMOVE_POLL_USE_RES = 2,
        IOU_POLL_REISSUE = 3,
};

/*
 * All poll tw should go through this. Checks for poll events, manages
 * references, does rewait, etc.
 *
 * Returns a negative error on failure. IOU_POLL_NO_ACTION when no action
 * require, which is either spurious wakeup or multishot CQE is served.
 * IOU_POLL_DONE when it's done with the request, then the mask is stored in
 * req->cqe.res. IOU_POLL_REMOVE_POLL_USE_RES indicates to remove multishot
 * poll and that the result is stored in req->cqe.
 */
static int io_poll_check_events(struct io_kiocb *req, struct io_tw_state *ts)
{
        int v;

        /* req->task == current here, checking PF_EXITING is safe */
        if (unlikely(req->task->flags & PF_EXITING))
                return -ECANCELED;

        do {
                v = atomic_read(&req->poll_refs);

                if (unlikely(v != 1)) {
                        /* tw should be the owner and so have some refs */
                        if (WARN_ON_ONCE(!(v & IO_POLL_REF_MASK)))
                                return IOU_POLL_NO_ACTION;
                        if (v & IO_POLL_CANCEL_FLAG)
                                return -ECANCELED;
                        /*
                         * cqe.res contains only events of the first wake up
                         * and all others are to be lost. Redo vfs_poll() to get
                         * up to date state.
                         */
                        if ((v & IO_POLL_REF_MASK) != 1)
                                req->cqe.res = 0;

                        if (v & IO_POLL_RETRY_FLAG) {
                                req->cqe.res = 0;
                                /*
                                 * We won't find new events that came in between
                                 * vfs_poll and the ref put unless we clear the
                                 * flag in advance.
                                 */
                                atomic_andnot(IO_POLL_RETRY_FLAG, &req->poll_refs);
                                v &= ~IO_POLL_RETRY_FLAG;
                        }
                }

                /* the mask was stashed in __io_poll_execute */
                if (!req->cqe.res) {
                        struct poll_table_struct pt = { ._key = req->apoll_events };
                        req->cqe.res = vfs_poll(req->file, &pt) & req->apoll_events;
                        /*
                         * We got woken with a mask, but someone else got to
                         * it first. The above vfs_poll() doesn't add us back
                         * to the waitqueue, so if we get nothing back, we
                         * should be safe and attempt a reissue.
                         */
                        if (unlikely(!req->cqe.res)) {
                                /* Multishot armed need not reissue */
                                if (!(req->apoll_events & EPOLLONESHOT))
                                        continue;
                                return IOU_POLL_REISSUE;
                        }
                }
                if (req->apoll_events & EPOLLONESHOT)
                        return IOU_POLL_DONE;

                /* multishot, just fill a CQE and proceed */
                if (!(req->flags & REQ_F_APOLL_MULTISHOT)) {
                        __poll_t mask = mangle_poll(req->cqe.res &
                                                    req->apoll_events);

                        if (!io_fill_cqe_req_aux(req, ts->locked, mask,
                                                 IORING_CQE_F_MORE)) {
                                io_req_set_res(req, mask, 0);
                                return IOU_POLL_REMOVE_POLL_USE_RES;
                        }
                } else {
                        int ret = io_poll_issue(req, ts);
                        if (ret == IOU_STOP_MULTISHOT)
                                return IOU_POLL_REMOVE_POLL_USE_RES;
                        if (ret < 0)
                                return ret;
                }

                /* force the next iteration to vfs_poll() */
                req->cqe.res = 0;

                /*
                 * Release all references, retry if someone tried to restart
                 * task_work while we were executing it.
                 */
        } while (atomic_sub_return(v & IO_POLL_REF_MASK, &req->poll_refs) &
                                        IO_POLL_REF_MASK);

        return IOU_POLL_NO_ACTION;
}

void io_poll_task_func(struct io_kiocb *req, struct io_tw_state *ts)
{
        int ret;

        ret = io_poll_check_events(req, ts);
        if (ret == IOU_POLL_NO_ACTION)
                return;
        io_poll_remove_entries(req);
        io_poll_tw_hash_eject(req, ts);

        if (req->opcode == IORING_OP_POLL_ADD) {
                if (ret == IOU_POLL_DONE) {
                        struct io_poll *poll;

                        poll = io_kiocb_to_cmd(req, struct io_poll);
                        req->cqe.res = mangle_poll(req->cqe.res & poll->events);
                } else if (ret == IOU_POLL_REISSUE) {
                        io_req_task_submit(req, ts);
                        return;
                } else if (ret != IOU_POLL_REMOVE_POLL_USE_RES) {
                        req->cqe.res = ret;
                        req_set_fail(req);
                }

                io_req_set_res(req, req->cqe.res, 0);
                io_req_task_complete(req, ts);
        } else {
                io_tw_lock(req->ctx, ts);

                if (ret == IOU_POLL_REMOVE_POLL_USE_RES)
                        io_req_task_complete(req, ts);
                else if (ret == IOU_POLL_DONE || ret == IOU_POLL_REISSUE)
                        io_req_task_submit(req, ts);
                else
                        io_req_defer_failed(req, ret);
        }
}

static void __io_poll_execute(struct io_kiocb *req, int mask)
{
        io_req_set_res(req, mask, 0);
        req->io_task_work.func = io_poll_task_func;

        trace_io_uring_task_add(req, mask);
        __io_req_task_work_add(req, IOU_F_TWQ_LAZY_WAKE);
}

static inline void io_poll_execute(struct io_kiocb *req, int res)
{
        if (io_poll_get_ownership(req))
                __io_poll_execute(req, res);
}

static void io_poll_cancel_req(struct io_kiocb *req)
{
        io_poll_mark_cancelled(req);
        /* kick tw, which should complete the request */
        io_poll_execute(req, 0);
}

#define IO_ASYNC_POLL_COMMON    (EPOLLONESHOT | EPOLLPRI)

static __cold int io_pollfree_wake(struct io_kiocb *req, struct io_poll *poll)
{
        io_poll_mark_cancelled(req);
        /* we have to kick tw in case it's not already */
        io_poll_execute(req, 0);

        /*
         * If the waitqueue is being freed early but someone is already
         * holds ownership over it, we have to tear down the request as
         * best we can. That means immediately removing the request from
         * its waitqueue and preventing all further accesses to the
         * waitqueue via the request.
         */
        list_del_init(&poll->wait.entry);

        /*
         * Careful: this *must* be the last step, since as soon
         * as req->head is NULL'ed out, the request can be
         * completed and freed, since aio_poll_complete_work()
         * will no longer need to take the waitqueue lock.
         */
        smp_store_release(&poll->head, NULL);
        return 1;
}

static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
                        void *key)
{
        struct io_kiocb *req = wqe_to_req(wait);
        struct io_poll *poll = container_of(wait, struct io_poll, wait);
        __poll_t mask = key_to_poll(key);

        if (unlikely(mask & POLLFREE))
                return io_pollfree_wake(req, poll);

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

        if (io_poll_get_ownership(req)) {
                /*
                 * If we trigger a multishot poll off our own wakeup path,
                 * disable multishot as there is a circular dependency between
                 * CQ posting and triggering the event.
                 */
                if (mask & EPOLL_URING_WAKE)
                        poll->events |= EPOLLONESHOT;

                /* optional, saves extra locking for removal in tw handler */
                if (mask && poll->events & EPOLLONESHOT) {
                        list_del_init(&poll->wait.entry);
                        poll->head = NULL;
                        if (wqe_is_double(wait))
                                req->flags &= ~REQ_F_DOUBLE_POLL;
                        else
                                req->flags &= ~REQ_F_SINGLE_POLL;
                }
                __io_poll_execute(req, mask);
        }
        return 1;
}

/* fails only when polling is already completing by the first entry */
static bool io_poll_double_prepare(struct io_kiocb *req)
{
        struct wait_queue_head *head;
        struct io_poll *poll = io_poll_get_single(req);

        /* head is RCU protected, see io_poll_remove_entries() comments */
        rcu_read_lock();
        head = smp_load_acquire(&poll->head);
        /*
         * poll arm might not hold ownership and so race for req->flags with
         * io_poll_wake(). There is only one poll entry queued, serialise with
         * it by taking its head lock. As we're still arming the tw hanlder
         * is not going to be run, so there are no races with it.
         */
        if (head) {
                spin_lock_irq(&head->lock);
                req->flags |= REQ_F_DOUBLE_POLL;
                if (req->opcode == IORING_OP_POLL_ADD)
                        req->flags |= REQ_F_ASYNC_DATA;
                spin_unlock_irq(&head->lock);
        }
        rcu_read_unlock();
        return !!head;
}

static void __io_queue_proc(struct io_poll *poll, struct io_poll_table *pt,
                            struct wait_queue_head *head,
                            struct io_poll **poll_ptr)
{
        struct io_kiocb *req = pt->req;
        unsigned long wqe_private = (unsigned long) req;

        /*
         * The file being polled uses multiple waitqueues for poll handling
         * (e.g. one for read, one for write). Setup a separate io_poll
         * if this happens.
         */
        if (unlikely(pt->nr_entries)) {
                struct io_poll *first = poll;

                /* double add on the same waitqueue head, ignore */
                if (first->head == head)
                        return;
                /* already have a 2nd entry, fail a third attempt */
                if (*poll_ptr) {
                        if ((*poll_ptr)->head == head)
                                return;
                        pt->error = -EINVAL;
                        return;
                }

                poll = kmalloc(sizeof(*poll), GFP_ATOMIC);
                if (!poll) {
                        pt->error = -ENOMEM;
                        return;
                }

                /* mark as double wq entry */
                wqe_private |= IO_WQE_F_DOUBLE;
                io_init_poll_iocb(poll, first->events);
                if (!io_poll_double_prepare(req)) {
                        /* the request is completing, just back off */
                        kfree(poll);
                        return;
                }
                *poll_ptr = poll;
        } else {
                /* fine to modify, there is no poll queued to race with us */
                req->flags |= REQ_F_SINGLE_POLL;
        }

        pt->nr_entries++;
        poll->head = head;
        poll->wait.private = (void *) wqe_private;

        if (poll->events & EPOLLEXCLUSIVE)
                add_wait_queue_exclusive(head, &poll->wait);
        else
                add_wait_queue(head, &poll->wait);
}

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);
        struct io_poll *poll = io_kiocb_to_cmd(pt->req, struct io_poll);

        __io_queue_proc(poll, pt, head,
                        (struct io_poll **) &pt->req->async_data);
}

static bool io_poll_can_finish_inline(struct io_kiocb *req,
                                      struct io_poll_table *pt)
{
        return pt->owning || io_poll_get_ownership(req);
}

static void io_poll_add_hash(struct io_kiocb *req)
{
        if (req->flags & REQ_F_HASH_LOCKED)
                io_poll_req_insert_locked(req);
        else
                io_poll_req_insert(req);
}

/*
 * Returns 0 when it's handed over for polling. The caller owns the requests if
 * it returns non-zero, but otherwise should not touch it. Negative values
 * contain an error code. When the result is >0, the polling has completed
 * inline and ipt.result_mask is set to the mask.
 */
static int __io_arm_poll_handler(struct io_kiocb *req,
                                 struct io_poll *poll,
                                 struct io_poll_table *ipt, __poll_t mask,
                                 unsigned issue_flags)
{
        struct io_ring_ctx *ctx = req->ctx;

        INIT_HLIST_NODE(&req->hash_node);
        req->work.cancel_seq = atomic_read(&ctx->cancel_seq);
        io_init_poll_iocb(poll, mask);
        poll->file = req->file;
        req->apoll_events = poll->events;

        ipt->pt._key = mask;
        ipt->req = req;
        ipt->error = 0;
        ipt->nr_entries = 0;
        /*
         * Polling is either completed here or via task_work, so if we're in the
         * task context we're naturally serialised with tw by merit of running
         * the same task. When it's io-wq, take the ownership to prevent tw
         * from running. However, when we're in the task context, skip taking
         * it as an optimisation.
         *
         * Note: even though the request won't be completed/freed, without
         * ownership we still can race with io_poll_wake().
         * io_poll_can_finish_inline() tries to deal with that.
         */
        ipt->owning = issue_flags & IO_URING_F_UNLOCKED;
        atomic_set(&req->poll_refs, (int)ipt->owning);

        /* io-wq doesn't hold uring_lock */
        if (issue_flags & IO_URING_F_UNLOCKED)
                req->flags &= ~REQ_F_HASH_LOCKED;

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

        if (unlikely(ipt->error || !ipt->nr_entries)) {
                io_poll_remove_entries(req);

                if (!io_poll_can_finish_inline(req, ipt)) {
                        io_poll_mark_cancelled(req);
                        return 0;
                } else if (mask && (poll->events & EPOLLET)) {
                        ipt->result_mask = mask;
                        return 1;
                }
                return ipt->error ?: -EINVAL;
        }

        if (mask &&
           ((poll->events & (EPOLLET|EPOLLONESHOT)) == (EPOLLET|EPOLLONESHOT))) {
                if (!io_poll_can_finish_inline(req, ipt)) {
                        io_poll_add_hash(req);
                        return 0;
                }
                io_poll_remove_entries(req);
                ipt->result_mask = mask;
                /* no one else has access to the req, forget about the ref */
                return 1;
        }

        io_poll_add_hash(req);

        if (mask && (poll->events & EPOLLET) &&
            io_poll_can_finish_inline(req, ipt)) {
                __io_poll_execute(req, mask);
                return 0;
        }

        if (ipt->owning) {
                /*
                 * Try to release ownership. If we see a change of state, e.g.
                 * poll was waken up, queue up a tw, it'll deal with it.
                 */
                if (atomic_cmpxchg(&req->poll_refs, 1, 0) != 1)
                        __io_poll_execute(req, 0);
        }
        return 0;
}

static void io_async_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);
        struct async_poll *apoll = pt->req->apoll;

        __io_queue_proc(&apoll->poll, pt, head, &apoll->double_poll);
}

/*
 * We can't reliably detect loops in repeated poll triggers and issue
 * subsequently failing. But rather than fail these immediately, allow a
 * certain amount of retries before we give up. Given that this condition
 * should _rarely_ trigger even once, we should be fine with a larger value.
 */
#define APOLL_MAX_RETRY         128

static struct async_poll *io_req_alloc_apoll(struct io_kiocb *req,
                                             unsigned issue_flags)
{
        struct io_ring_ctx *ctx = req->ctx;
        struct io_cache_entry *entry;
        struct async_poll *apoll;

        if (req->flags & REQ_F_POLLED) {
                apoll = req->apoll;
                kfree(apoll->double_poll);
        } else if (!(issue_flags & IO_URING_F_UNLOCKED)) {
                entry = io_alloc_cache_get(&ctx->apoll_cache);
                if (entry == NULL)
                        goto alloc_apoll;
                apoll = container_of(entry, struct async_poll, cache);
                apoll->poll.retries = APOLL_MAX_RETRY;
        } else {
alloc_apoll:
                apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);
                if (unlikely(!apoll))
                        return NULL;
                apoll->poll.retries = APOLL_MAX_RETRY;
        }
        apoll->double_poll = NULL;
        req->apoll = apoll;
        if (unlikely(!--apoll->poll.retries))
                return NULL;
        return apoll;
}

int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
{
        const struct io_issue_def *def = &io_issue_defs[req->opcode];
        struct async_poll *apoll;
        struct io_poll_table ipt;
        __poll_t mask = POLLPRI | POLLERR | EPOLLET;
        int ret;

        /*
         * apoll requests already grab the mutex to complete in the tw handler,
         * so removal from the mutex-backed hash is free, use it by default.
         */
        req->flags |= REQ_F_HASH_LOCKED;

        if (!def->pollin && !def->pollout)
                return IO_APOLL_ABORTED;
        if (!file_can_poll(req->file))
                return IO_APOLL_ABORTED;
        if (!(req->flags & REQ_F_APOLL_MULTISHOT))
                mask |= EPOLLONESHOT;

        if (def->pollin) {
                mask |= EPOLLIN | EPOLLRDNORM;

                /* If reading from MSG_ERRQUEUE using recvmsg, ignore POLLIN */
                if (req->flags & REQ_F_CLEAR_POLLIN)
                        mask &= ~EPOLLIN;
        } else {
                mask |= EPOLLOUT | EPOLLWRNORM;
        }
        if (def->poll_exclusive)
                mask |= EPOLLEXCLUSIVE;

        apoll = io_req_alloc_apoll(req, issue_flags);
        if (!apoll)
                return IO_APOLL_ABORTED;
        req->flags &= ~(REQ_F_SINGLE_POLL | REQ_F_DOUBLE_POLL);
        req->flags |= REQ_F_POLLED;
        ipt.pt._qproc = io_async_queue_proc;

        io_kbuf_recycle(req, issue_flags);

        ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask, issue_flags);
        if (ret)
                return ret > 0 ? IO_APOLL_READY : IO_APOLL_ABORTED;
        trace_io_uring_poll_arm(req, mask, apoll->poll.events);
        return IO_APOLL_OK;
}

static __cold bool io_poll_remove_all_table(struct task_struct *tsk,
                                            struct io_hash_table *table,
                                            bool cancel_all)
{
        unsigned nr_buckets = 1U << table->hash_bits;
        struct hlist_node *tmp;
        struct io_kiocb *req;
        bool found = false;
        int i;

        for (i = 0; i < nr_buckets; i++) {
                struct io_hash_bucket *hb = &table->hbs[i];

                spin_lock(&hb->lock);
                hlist_for_each_entry_safe(req, tmp, &hb->list, hash_node) {
                        if (io_match_task_safe(req, tsk, cancel_all)) {
                                hlist_del_init(&req->hash_node);
                                io_poll_cancel_req(req);
                                found = true;
                        }
                }
                spin_unlock(&hb->lock);
        }
        return found;
}

/*
 * Returns true if we found and killed one or more poll requests
 */
__cold bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk,
                               bool cancel_all)
        __must_hold(&ctx->uring_lock)
{
        bool ret;

        ret = io_poll_remove_all_table(tsk, &ctx->cancel_table, cancel_all);
        ret |= io_poll_remove_all_table(tsk, &ctx->cancel_table_locked, cancel_all);
        return ret;
}

static struct io_kiocb *io_poll_find(struct io_ring_ctx *ctx, bool poll_only,
                                     struct io_cancel_data *cd,
                                     struct io_hash_table *table,
                                     struct io_hash_bucket **out_bucket)
{
        struct io_kiocb *req;
        u32 index = hash_long(cd->data, table->hash_bits);
        struct io_hash_bucket *hb = &table->hbs[index];

        *out_bucket = NULL;

        spin_lock(&hb->lock);
        hlist_for_each_entry(req, &hb->list, hash_node) {
                if (cd->data != req->cqe.user_data)
                        continue;
                if (poll_only && req->opcode != IORING_OP_POLL_ADD)
                        continue;
                if (cd->flags & IORING_ASYNC_CANCEL_ALL) {
                        if (cd->seq == req->work.cancel_seq)
                                continue;
                        req->work.cancel_seq = cd->seq;
                }
                *out_bucket = hb;
                return req;
        }
        spin_unlock(&hb->lock);
        return NULL;
}

static struct io_kiocb *io_poll_file_find(struct io_ring_ctx *ctx,
                                          struct io_cancel_data *cd,
                                          struct io_hash_table *table,
                                          struct io_hash_bucket **out_bucket)
{
        unsigned nr_buckets = 1U << table->hash_bits;
        struct io_kiocb *req;
        int i;

        *out_bucket = NULL;

        for (i = 0; i < nr_buckets; i++) {
                struct io_hash_bucket *hb = &table->hbs[i];

                spin_lock(&hb->lock);
                hlist_for_each_entry(req, &hb->list, hash_node) {
                        if (io_cancel_req_match(req, cd)) {
                                *out_bucket = hb;
                                return req;
                        }
                }
                spin_unlock(&hb->lock);
        }
        return NULL;
}

static int io_poll_disarm(struct io_kiocb *req)
{
        if (!req)
                return -ENOENT;
        if (!io_poll_get_ownership(req))
                return -EALREADY;
        io_poll_remove_entries(req);
        hash_del(&req->hash_node);
        return 0;
}

static int __io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
                            struct io_hash_table *table)
{
        struct io_hash_bucket *bucket;
        struct io_kiocb *req;

        if (cd->flags & (IORING_ASYNC_CANCEL_FD | IORING_ASYNC_CANCEL_OP |
                         IORING_ASYNC_CANCEL_ANY))
                req = io_poll_file_find(ctx, cd, table, &bucket);
        else
                req = io_poll_find(ctx, false, cd, table, &bucket);

        if (req)
                io_poll_cancel_req(req);
        if (bucket)
                spin_unlock(&bucket->lock);
        return req ? 0 : -ENOENT;
}

int io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
                   unsigned issue_flags)
{
        int ret;

        ret = __io_poll_cancel(ctx, cd, &ctx->cancel_table);
        if (ret != -ENOENT)
                return ret;

        io_ring_submit_lock(ctx, issue_flags);
        ret = __io_poll_cancel(ctx, cd, &ctx->cancel_table_locked);
        io_ring_submit_unlock(ctx, issue_flags);
        return ret;
}

static __poll_t io_poll_parse_events(const struct io_uring_sqe *sqe,
                                     unsigned int flags)
{
        u32 events;

        events = READ_ONCE(sqe->poll32_events);
#ifdef __BIG_ENDIAN
        events = swahw32(events);
#endif
        if (!(flags & IORING_POLL_ADD_MULTI))
                events |= EPOLLONESHOT;
        if (!(flags & IORING_POLL_ADD_LEVEL))
                events |= EPOLLET;
        return demangle_poll(events) |
                (events & (EPOLLEXCLUSIVE|EPOLLONESHOT|EPOLLET));
}

int io_poll_remove_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_poll_update *upd = io_kiocb_to_cmd(req, struct io_poll_update);
        u32 flags;

        if (sqe->buf_index || sqe->splice_fd_in)
                return -EINVAL;
        flags = READ_ONCE(sqe->len);
        if (flags & ~(IORING_POLL_UPDATE_EVENTS | IORING_POLL_UPDATE_USER_DATA |
                      IORING_POLL_ADD_MULTI))
                return -EINVAL;
        /* meaningless without update */
        if (flags == IORING_POLL_ADD_MULTI)
                return -EINVAL;

        upd->old_user_data = READ_ONCE(sqe->addr);
        upd->update_events = flags & IORING_POLL_UPDATE_EVENTS;
        upd->update_user_data = flags & IORING_POLL_UPDATE_USER_DATA;

        upd->new_user_data = READ_ONCE(sqe->off);
        if (!upd->update_user_data && upd->new_user_data)
                return -EINVAL;
        if (upd->update_events)
                upd->events = io_poll_parse_events(sqe, flags);
        else if (sqe->poll32_events)
                return -EINVAL;

        return 0;
}

int io_poll_add_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
        struct io_poll *poll = io_kiocb_to_cmd(req, struct io_poll);
        u32 flags;

        if (sqe->buf_index || sqe->off || sqe->addr)
                return -EINVAL;
        flags = READ_ONCE(sqe->len);
        if (flags & ~IORING_POLL_ADD_MULTI)
                return -EINVAL;
        if ((flags & IORING_POLL_ADD_MULTI) && (req->flags & REQ_F_CQE_SKIP))
                return -EINVAL;

        poll->events = io_poll_parse_events(sqe, flags);
        return 0;
}

int io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_poll *poll = io_kiocb_to_cmd(req, struct io_poll);
        struct io_poll_table ipt;
        int ret;

        ipt.pt._qproc = io_poll_queue_proc;

        /*
         * If sqpoll or single issuer, there is no contention for ->uring_lock
         * and we'll end up holding it in tw handlers anyway.
         */
        if (req->ctx->flags & (IORING_SETUP_SQPOLL|IORING_SETUP_SINGLE_ISSUER))
                req->flags |= REQ_F_HASH_LOCKED;

        ret = __io_arm_poll_handler(req, poll, &ipt, poll->events, issue_flags);
        if (ret > 0) {
                io_req_set_res(req, ipt.result_mask, 0);
                return IOU_OK;
        }
        return ret ?: IOU_ISSUE_SKIP_COMPLETE;
}

int io_poll_remove(struct io_kiocb *req, unsigned int issue_flags)
{
        struct io_poll_update *poll_update = io_kiocb_to_cmd(req, struct io_poll_update);
        struct io_ring_ctx *ctx = req->ctx;
        struct io_cancel_data cd = { .ctx = ctx, .data = poll_update->old_user_data, };
        struct io_hash_bucket *bucket;
        struct io_kiocb *preq;
        int ret2, ret = 0;
        struct io_tw_state ts = { .locked = true };

        io_ring_submit_lock(ctx, issue_flags);
        preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table, &bucket);
        ret2 = io_poll_disarm(preq);
        if (bucket)
                spin_unlock(&bucket->lock);
        if (!ret2)
                goto found;
        if (ret2 != -ENOENT) {
                ret = ret2;
                goto out;
        }

        preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table_locked, &bucket);
        ret2 = io_poll_disarm(preq);
        if (bucket)
                spin_unlock(&bucket->lock);
        if (ret2) {
                ret = ret2;
                goto out;
        }

found:
        if (WARN_ON_ONCE(preq->opcode != IORING_OP_POLL_ADD)) {
                ret = -EFAULT;
                goto out;
        }

        if (poll_update->update_events || poll_update->update_user_data) {
                /* only mask one event flags, keep behavior flags */
                if (poll_update->update_events) {
                        struct io_poll *poll = io_kiocb_to_cmd(preq, struct io_poll);

                        poll->events &= ~0xffff;
                        poll->events |= poll_update->events & 0xffff;
                        poll->events |= IO_POLL_UNMASK;
                }
                if (poll_update->update_user_data)
                        preq->cqe.user_data = poll_update->new_user_data;

                ret2 = io_poll_add(preq, issue_flags & ~IO_URING_F_UNLOCKED);
                /* successfully updated, don't complete poll request */
                if (!ret2 || ret2 == -EIOCBQUEUED)
                        goto out;
        }

        req_set_fail(preq);
        io_req_set_res(preq, -ECANCELED, 0);
        io_req_task_complete(preq, &ts);
out:
        io_ring_submit_unlock(ctx, issue_flags);
        if (ret < 0) {
                req_set_fail(req);
                return ret;
        }
        /* complete update request, we're done with it */
        io_req_set_res(req, ret, 0);
        return IOU_OK;
}

void io_apoll_cache_free(struct io_cache_entry *entry)
{
        kfree(container_of(entry, struct async_poll, cache));
}