From: Jens Axboe axboe@kernel.dk
commit 8caa03f10bf92cb8657408a6ece6a8a73f96ce13 upstream.
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: 6e5aedb9324a ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- io_uring/poll.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- a/io_uring/poll.c +++ b/io_uring/poll.c @@ -281,8 +281,12 @@ static int io_poll_check_events(struct i * 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;