Commit 8caa03f1 authored Jan 20, 2023 by Jens Axboe

io_uring/poll: don't reissue in case of poll race on multishot request

A previous commit fixed a poll race that can occur, but it's only
applicable for multishot requests. For a multishot request, we can safely
ignore a spurious wakeup, as we never leave the waitqueue to begin with.

A blunt reissue of a multishot armed request can cause us to leak a
buffer, if they are ring provided. While this seems like a bug in itself,
it's not really defined behavior to reissue a multishot request directly.
It's less efficient to do so as well, and not required to rearm anything
like it is for singleshot poll requests.

Cc: stable@vger.kernel.org
Fixes: 6e5aedb9 ("io_uring/poll: attempt request issue after racy poll wakeup")
Reported-and-tested-by: Olivier Langlois <olivier@trillion01.com>
Link: https://github.com/axboe/liburing/issues/778

Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 8579538c

io_uring/poll.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -283,9 +283,13 @@ static int io_poll_check_events(struct io_kiocb req, bool locked)
		* to the waitqueue, so if we get nothing back, we
		* should be safe and attempt a reissue.
		*/
		if (unlikely(!req->cqe.res))
		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;