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io_uring: don't miss setting REQ_F_DOUBLE_POLL 

When adding a second poll entry we should set REQ_F_DOUBLE_POLL
unconditionally. We might race with the first entry removal but that
doesn't change the rule.

Fixes: a18427bb2d9b ("io_uring: optimise submission side poll_refs")
Reported-and-tested-by: syzbot+49950ba66096b1f0209b@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8b680d83ded07424db83e8745585e7a6d72826ef.1657203020.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2022-07-07 15:13:14 +01:00 committed by Jens Axboe
parent cf0dd9527e
commit 7a121ced6e
1 changed files with 10 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
io_uring/poll.c
View File

@ -401,16 +401,18 @@ static void io_poll_double_prepare(struct io_kiocb *req)
/* head is RCU protected, see io_poll_remove_entries() comments */
rcu_read_lock();
head = smp_load_acquire(&poll->head);
if (head) {
/*
* poll arm may not hold ownership and so race with
* io_poll_wake() by modifying req->flags. There is only one
* poll entry queued, serialise with it by taking its head lock.
*/
/*
* poll arm may not hold ownership and so race with
* io_poll_wake() by modifying req->flags. There is only one
* poll entry queued, serialise with it by taking its head lock.
*/
if (head)
spin_lock_irq(&head->lock);
req->flags |= REQ_F_DOUBLE_POLL;
req->flags |= REQ_F_DOUBLE_POLL;
if (head)
spin_unlock_irq(&head->lock);
}
rcu_read_unlock();
}