This is a note to let you know that I've just added the patch titled io_uring: pass in EPOLL_URING_WAKE for eventfd signaling and wakeups to the 6.1-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: io_uring-pass-in-epoll_uring_wake-for-eventfd-signal.patch and it can be found in the queue-6.1 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 2d15b0d0467a3f2a6f468ae6563fe3f93f0ae1a3 Author: Jens Axboe <axboe@xxxxxxxxx> Date: Sun Nov 20 10:18:45 2022 -0700 io_uring: pass in EPOLL_URING_WAKE for eventfd signaling and wakeups [ Upstream commit 4464853277d0ccdb9914608dd1332f0fa2f9846f ] Pass in EPOLL_URING_WAKE when signaling eventfd or doing poll related wakups, so that we can check for a circular event dependency between eventfd and epoll. If this flag is set when our wakeup handlers are called, then we know we have a dependency that needs to terminate multishot requests. eventfd and epoll are the only such possible dependencies. Cc: stable@xxxxxxxxxxxxxxx # 6.0 Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 17771cb3c333..71f1cabb9f3d 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -495,7 +495,7 @@ static void io_eventfd_ops(struct rcu_head *rcu) int ops = atomic_xchg(&ev_fd->ops, 0); if (ops & BIT(IO_EVENTFD_OP_SIGNAL_BIT)) - eventfd_signal(ev_fd->cq_ev_fd, 1); + eventfd_signal_mask(ev_fd->cq_ev_fd, 1, EPOLL_URING_WAKE); /* IO_EVENTFD_OP_FREE_BIT may not be set here depending on callback * ordering in a race but if references are 0 we know we have to free @@ -531,7 +531,7 @@ static void io_eventfd_signal(struct io_ring_ctx *ctx) goto out; if (likely(eventfd_signal_allowed())) { - eventfd_signal(ev_fd->cq_ev_fd, 1); + eventfd_signal_mask(ev_fd->cq_ev_fd, 1, EPOLL_URING_WAKE); } else { atomic_inc(&ev_fd->refs); if (!atomic_fetch_or(BIT(IO_EVENTFD_OP_SIGNAL_BIT), &ev_fd->ops)) diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h index 50bc3af44953..4334cd30c423 100644 --- a/io_uring/io_uring.h +++ b/io_uring/io_uring.h @@ -4,6 +4,7 @@ #include <linux/errno.h> #include <linux/lockdep.h> #include <linux/io_uring_types.h> +#include <uapi/linux/eventpoll.h> #include "io-wq.h" #include "slist.h" #include "filetable.h" @@ -207,12 +208,18 @@ static inline void io_commit_cqring(struct io_ring_ctx *ctx) static inline void __io_cqring_wake(struct io_ring_ctx *ctx) { /* - * wake_up_all() may seem excessive, but io_wake_function() and - * io_should_wake() handle the termination of the loop and only - * wake as many waiters as we need to. + * Trigger waitqueue handler on all waiters on our waitqueue. This + * won't necessarily wake up all the tasks, io_should_wake() will make + * that decision. + * + * Pass in EPOLLIN|EPOLL_URING_WAKE as the poll wakeup key. The latter + * set in the mask so that if we recurse back into our own poll + * waitqueue handlers, we know we have a dependency between eventfd or + * epoll and should terminate multishot poll at that point. */ if (waitqueue_active(&ctx->cq_wait)) - wake_up_all(&ctx->cq_wait); + __wake_up(&ctx->cq_wait, TASK_NORMAL, 0, + poll_to_key(EPOLL_URING_WAKE | EPOLLIN)); } static inline void io_cqring_wake(struct io_ring_ctx *ctx) diff --git a/io_uring/poll.c b/io_uring/poll.c index d9bf1767867e..fded1445a803 100644 --- a/io_uring/poll.c +++ b/io_uring/poll.c @@ -429,6 +429,14 @@ static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync, return 0; if (io_poll_get_ownership(req)) { + /* + * If we trigger a multishot poll off our own wakeup path, + * disable multishot as there is a circular dependency between + * CQ posting and triggering the event. + */ + if (mask & EPOLL_URING_WAKE) + poll->events |= EPOLLONESHOT; + /* optional, saves extra locking for removal in tw handler */ if (mask && poll->events & EPOLLONESHOT) { list_del_init(&poll->wait.entry);