io_uring/poll: serialize poll linked timer start with poll removal

Commit ef7dfac51d8ed961b742218f526bd589f3900a59 upstream.

We selectively grab the ctx->uring_lock for poll update/removal, but
we really should grab it from the start to fully synchronize with
linked timeouts. Normally this is indeed the case, but if requests
are forced async by the application, we don't fully cover removal
and timer disarm within the uring_lock.

Make this simpler by having consistent locking state for poll removal.

Cc: stable@vger.kernel.org # 6.1+
Reported-by: Querijn Voet <querijnqyn@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/io_uring/poll.c b/io_uring/poll.c
index 4788073..869e1d2 100644 (file)
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -993,8 +993,9 @@ int io_poll_remove(struct io_kiocb *req, unsigned int issue_flags)
        struct io_hash_bucket *bucket;
        struct io_kiocb *preq;
        int ret2, ret = 0;
-       bool locked;
+       bool 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)
@@ -1006,12 +1007,10 @@ int io_poll_remove(struct io_kiocb *req, unsigned int issue_flags)
                goto out;
        }
 
-       io_ring_submit_lock(ctx, issue_flags);
        preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table_locked, &bucket);
        ret2 = io_poll_disarm(preq);
        if (bucket)
                spin_unlock(&bucket->lock);
-       io_ring_submit_unlock(ctx, issue_flags);
        if (ret2) {
                ret = ret2;
                goto out;
@@ -1035,7 +1034,7 @@ found:
                if (poll_update->update_user_data)
                        preq->cqe.user_data = poll_update->new_user_data;
 
-               ret2 = io_poll_add(preq, issue_flags);
+               ret2 = io_poll_add(preq, issue_flags & ~IO_URING_F_UNLOCKED);
                /* successfully updated, don't complete poll request */
                if (!ret2 || ret2 == -EIOCBQUEUED)
                        goto out;
@@ -1043,9 +1042,9 @@ found:
 
        req_set_fail(preq);
        io_req_set_res(preq, -ECANCELED, 0);
-       locked = !(issue_flags & IO_URING_F_UNLOCKED);
        io_req_task_complete(preq, &locked);
 out:
+       io_ring_submit_unlock(ctx, issue_flags);
        if (ret < 0) {
                req_set_fail(req);
                return ret;