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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: 6e5aedb932 ("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>
This commit is contained in:
Jens Axboe 2023-01-20 15:08:21 -07:00
parent 8579538c89
commit 8caa03f10b
1 changed files with 5 additions and 1 deletions
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6
io_uring/poll.c
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@ -283,8 +283,12 @@ 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;