FAILED: patch "[PATCH] io_uring/eventfd: ensure io_eventfd_signal() defers another" failed to apply to 6.1-stable tree

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 <[email protected]>.

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 c9a40292a44e78f71258b8522655bffaf5753bdb
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025011246-appealing-angler-4f22@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c9a40292a44e78f71258b8522655bffaf5753bdb Mon Sep 17 00:00:00 2001
From: Jens Axboe <[email protected]>
Date: Wed, 8 Jan 2025 10:28:05 -0700
Subject: [PATCH] io_uring/eventfd: ensure io_eventfd_signal() defers another
RCU period

io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period.

Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.

index fab936d31ba8..100d5da94cb9 100644
@@ -33,20 +33,18 @@ static void io_eventfd_free(struct rcu_head *rcu)
 	kfree(ev_fd);
 }
 
+static void io_eventfd_put(struct io_ev_fd *ev_fd)
+{
+	if (refcount_dec_and_test(&ev_fd->refs))
+		call_rcu(&ev_fd->rcu, io_eventfd_free);
+}
+
 static void io_eventfd_do_signal(struct rcu_head *rcu)
 {
 	struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu);
 
 	eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE);
-
-	if (refcount_dec_and_test(&ev_fd->refs))
-		io_eventfd_free(rcu);
-}
-
-static void io_eventfd_put(struct io_ev_fd *ev_fd)
-{
-	if (refcount_dec_and_test(&ev_fd->refs))
-		call_rcu(&ev_fd->rcu, io_eventfd_free);
+	io_eventfd_put(ev_fd);
 }
 
 static void io_eventfd_release(struct io_ev_fd *ev_fd, bool put_ref)

And here's the 6.1 version.

Jens Axboe

From a812a6531595d7e0412c4f05ede6032f04c86ef7 Mon Sep 17 00:00:00 2001
From: Jens Axboe <[email protected]>
Date: Wed, 8 Jan 2025 11:16:13 -0700
Subject: [PATCH] io_uring/eventfd: ensure io_eventfd_signal() defers another
RCU period

Commit c9a40292a44e78f71258b8522655bffaf5753bdb upstream.

io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period.

Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.

---
 io_uring/io_uring.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

index 9b58ba4616d4..480752fc3eb6 100644
@@ -479,6 +479,13 @@ static __cold void io_queue_deferred(struct io_ring_ctx *ctx)
 	}
 }
 
+static void io_eventfd_free(struct rcu_head *rcu)
+{
+	struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu);
+
+	eventfd_ctx_put(ev_fd->cq_ev_fd);
+	kfree(ev_fd);
+}
 
 static void io_eventfd_ops(struct rcu_head *rcu)
 {

@@ -492,10 +499,8 @@ static void io_eventfd_ops(struct rcu_head *rcu)
 	 * ordering in a race but if references are 0 we know we have to free
 	 * it regardless.
 	 */
-	if (atomic_dec_and_test(&ev_fd->refs)) {
-		eventfd_ctx_put(ev_fd->cq_ev_fd);
-		kfree(ev_fd);
-	}
+	if (atomic_dec_and_test(&ev_fd->refs))
+		call_rcu(&ev_fd->rcu, io_eventfd_free);
 }
 
 static void io_eventfd_signal(struct io_ring_ctx *ctx)

2.47.1

Thanks, all 3 now queued up.

greg k-h

Thanks Greg!

Jens Axboe