Pass in EPOLL_URING 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>
---
io_uring/io_uring.c | 4 ++--
io_uring/io_uring.h | 15 +++++++++++----
io_uring/poll.c | 8 ++++++++
3 files changed, 21 insertions(+), 6 deletions(-)
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8840cf3e20f2..53d0043b77a5 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);
/* 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);
} 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 cef5ff924e63..f6cf74cd692b 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 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 | 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 055632e9092a..b5d9426c60f6 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -394,6 +394,14 @@ 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)
+ poll->events |= EPOLLONESHOT;
+
/* optional, saves extra locking for removal in tw handler */
if (mask && poll->events & EPOLLONESHOT) {
list_del_init(&poll->wait.entry);
--
2.35.1
