[PATCH 5.10 63/63] io_uring: pass in EPOLL_URING_WAKE for eventfd signaling and wakeups

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: Jens Axboe <axboe@xxxxxxxxx>

[ 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: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 io_uring/io_uring.c |   27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1626,13 +1626,15 @@ static void io_cqring_ev_posted(struct i
 	 * wake as many waiters as we need to.
 	 */
 	if (wq_has_sleeper(&ctx->cq_wait))
-		wake_up_all(&ctx->cq_wait);
+		__wake_up(&ctx->cq_wait, TASK_NORMAL, 0,
+				poll_to_key(EPOLL_URING_WAKE | EPOLLIN));
 	if (ctx->sq_data && waitqueue_active(&ctx->sq_data->wait))
 		wake_up(&ctx->sq_data->wait);
 	if (io_should_trigger_evfd(ctx))
-		eventfd_signal(ctx->cq_ev_fd, 1);
+		eventfd_signal_mask(ctx->cq_ev_fd, 1, EPOLL_URING_WAKE);
 	if (waitqueue_active(&ctx->poll_wait))
-		wake_up_interruptible(&ctx->poll_wait);
+		__wake_up(&ctx->poll_wait, TASK_INTERRUPTIBLE, 0,
+				poll_to_key(EPOLL_URING_WAKE | EPOLLIN));
 }
 
 static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx)
@@ -1642,12 +1644,14 @@ static void io_cqring_ev_posted_iopoll(s
 
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
 		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));
 	}
 	if (io_should_trigger_evfd(ctx))
-		eventfd_signal(ctx->cq_ev_fd, 1);
+		eventfd_signal_mask(ctx->cq_ev_fd, 1, EPOLL_URING_WAKE);
 	if (waitqueue_active(&ctx->poll_wait))
-		wake_up_interruptible(&ctx->poll_wait);
+		__wake_up(&ctx->poll_wait, TASK_INTERRUPTIBLE, 0,
+				poll_to_key(EPOLL_URING_WAKE | EPOLLIN));
 }
 
 /* Returns true if there are no backlogged entries after the flush */
@@ -5477,8 +5481,17 @@ static int io_poll_wake(struct wait_queu
 	if (mask && !(mask & poll->events))
 		return 0;
 
-	if (io_poll_get_ownership(req))
+	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;
+
 		__io_poll_execute(req, mask);
+	}
 	return 1;
 }