Patch "eventpoll: add EPOLL_URING_WAKE poll wakeup flag" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    eventpoll: add EPOLL_URING_WAKE poll wakeup flag

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:
     eventpoll-add-epoll_uring_wake-poll-wakeup-flag.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 3582fb5f42ec83305c6506be4db4450edc0de53c
Author: Jens Axboe <axboe@xxxxxxxxx>
Date:   Sun Nov 20 10:10:53 2022 -0700

    eventpoll: add EPOLL_URING_WAKE poll wakeup flag
    
    [ Upstream commit caf1aeaffc3b09649a56769e559333ae2c4f1802 ]
    
    We can have dependencies between epoll and io_uring. Consider an epoll
    context, identified by the epfd file descriptor, and an io_uring file
    descriptor identified by iofd. If we add iofd to the epfd context, and
    arm a multishot poll request for epfd with iofd, then the multishot
    poll request will repeatedly trigger and generate events until terminated
    by CQ ring overflow. This isn't a desired behavior.
    
    Add EPOLL_URING so that io_uring can pass it in as part of the poll wakeup
    key, and io_uring can check for that to detect a potential recursive
    invocation.
    
    Cc: stable@xxxxxxxxxxxxxxx # 6.0
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Stable-dep-of: 4464853277d0 ("io_uring: pass in EPOLL_URING_WAKE for eventfd signaling and wakeups")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 52954d4637b5..64659b110973 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -491,7 +491,8 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
  */
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
-static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
+static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi,
+			     unsigned pollflags)
 {
 	struct eventpoll *ep_src;
 	unsigned long flags;
@@ -522,16 +523,17 @@ static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
 	}
 	spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests);
 	ep->nests = nests + 1;
-	wake_up_locked_poll(&ep->poll_wait, EPOLLIN);
+	wake_up_locked_poll(&ep->poll_wait, EPOLLIN | pollflags);
 	ep->nests = 0;
 	spin_unlock_irqrestore(&ep->poll_wait.lock, flags);
 }
 
 #else
 
-static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
+static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi,
+			     unsigned pollflags)
 {
-	wake_up_poll(&ep->poll_wait, EPOLLIN);
+	wake_up_poll(&ep->poll_wait, EPOLLIN | pollflags);
 }
 
 #endif
@@ -742,7 +744,7 @@ static void ep_free(struct eventpoll *ep)
 
 	/* We need to release all tasks waiting for these file */
 	if (waitqueue_active(&ep->poll_wait))
-		ep_poll_safewake(ep, NULL);
+		ep_poll_safewake(ep, NULL, 0);
 
 	/*
 	 * We need to lock this because we could be hit by
@@ -1208,7 +1210,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
 
 	/* We have to call this outside the lock */
 	if (pwake)
-		ep_poll_safewake(ep, epi);
+		ep_poll_safewake(ep, epi, pollflags & EPOLL_URING_WAKE);
 
 	if (!(epi->event.events & EPOLLEXCLUSIVE))
 		ewake = 1;
@@ -1553,7 +1555,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
 
 	/* We have to call this outside the lock */
 	if (pwake)
-		ep_poll_safewake(ep, NULL);
+		ep_poll_safewake(ep, NULL, 0);
 
 	return 0;
 }
@@ -1629,7 +1631,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,
 
 	/* We have to call this outside the lock */
 	if (pwake)
-		ep_poll_safewake(ep, NULL);
+		ep_poll_safewake(ep, NULL, 0);
 
 	return 0;
 }
diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h
index 8a3432d0f0dc..e687658843b1 100644
--- a/include/uapi/linux/eventpoll.h
+++ b/include/uapi/linux/eventpoll.h
@@ -41,6 +41,12 @@
 #define EPOLLMSG	(__force __poll_t)0x00000400
 #define EPOLLRDHUP	(__force __poll_t)0x00002000
 
+/*
+ * Internal flag - wakeup generated by io_uring, used to detect recursion back
+ * into the io_uring poll handler.
+ */
+#define EPOLL_URING_WAKE	((__force __poll_t)(1U << 27))
+
 /* Set exclusive wakeup mode for the target file descriptor */
 #define EPOLLEXCLUSIVE	((__force __poll_t)(1U << 28))
 



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