The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x c16bda37594f83147b167d381d54c010024efecf # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '167809981810941@xxxxxxxxx' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: c16bda37594f ("io_uring/poll: allow some retries for poll triggering spuriously") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From c16bda37594f83147b167d381d54c010024efecf Mon Sep 17 00:00:00 2001 From: Jens Axboe <axboe@xxxxxxxxx> Date: Sat, 25 Feb 2023 12:53:53 -0700 Subject: [PATCH] io_uring/poll: allow some retries for poll triggering spuriously If we get woken spuriously when polling and fail the operation with -EAGAIN again, then we generally only allow polling again if data had been transferred at some point. This is indicated with REQ_F_PARTIAL_IO. However, if the spurious poll triggers when the socket was originally empty, then we haven't transferred data yet and we will fail the poll re-arm. This either punts the socket to io-wq if it's blocking, or it fails the request with -EAGAIN if not. Neither condition is desirable, as the former will slow things down, while the latter will make the application confused. We want to ensure that a repeated poll trigger doesn't lead to infinite work making no progress, that's what the REQ_F_PARTIAL_IO check was for. But it doesn't protect against a loop post the first receive, and it's unnecessarily strict if we started out with an empty socket. Add a somewhat random retry count, just to put an upper limit on the potential number of retries that will be done. This should be high enough that we won't really hit it in practice, unless something needs to be aborted anyway. Cc: stable@xxxxxxxxxxxxxxx # v5.10+ Link: https://github.com/axboe/liburing/issues/364 Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> diff --git a/io_uring/poll.c b/io_uring/poll.c index 8339a92b4510..a82d6830bdfd 100644 --- a/io_uring/poll.c +++ b/io_uring/poll.c @@ -650,6 +650,14 @@ static void io_async_queue_proc(struct file *file, struct wait_queue_head *head, __io_queue_proc(&apoll->poll, pt, head, &apoll->double_poll); } +/* + * We can't reliably detect loops in repeated poll triggers and issue + * subsequently failing. But rather than fail these immediately, allow a + * certain amount of retries before we give up. Given that this condition + * should _rarely_ trigger even once, we should be fine with a larger value. + */ +#define APOLL_MAX_RETRY 128 + static struct async_poll *io_req_alloc_apoll(struct io_kiocb *req, unsigned issue_flags) { @@ -665,14 +673,18 @@ static struct async_poll *io_req_alloc_apoll(struct io_kiocb *req, if (entry == NULL) goto alloc_apoll; apoll = container_of(entry, struct async_poll, cache); + apoll->poll.retries = APOLL_MAX_RETRY; } else { alloc_apoll: apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC); if (unlikely(!apoll)) return NULL; + apoll->poll.retries = APOLL_MAX_RETRY; } apoll->double_poll = NULL; req->apoll = apoll; + if (unlikely(!--apoll->poll.retries)) + return NULL; return apoll; } @@ -694,8 +706,6 @@ int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags) return IO_APOLL_ABORTED; if (!file_can_poll(req->file)) return IO_APOLL_ABORTED; - if ((req->flags & (REQ_F_POLLED|REQ_F_PARTIAL_IO)) == REQ_F_POLLED) - return IO_APOLL_ABORTED; if (!(req->flags & REQ_F_APOLL_MULTISHOT)) mask |= EPOLLONESHOT; diff --git a/io_uring/poll.h b/io_uring/poll.h index 5f3bae50fc81..b2393b403a2c 100644 --- a/io_uring/poll.h +++ b/io_uring/poll.h @@ -12,6 +12,7 @@ struct io_poll { struct file *file; struct wait_queue_head *head; __poll_t events; + int retries; struct wait_queue_entry wait; };
