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

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org>.

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 '<stable@vger.kernel.org>' --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 <axboe@kernel.dk>
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.

Fixes: 21a091b970cd ("io_uring: signal registered eventfd to process deferred task work")
Reported-by: Jann Horn <jannh@google.com>
Cc: stable@vger.kernel.org
Tested-by: Li Zetao <lizetao1@huawei.com>
Reviewed-by: Li Zetao<lizetao1@huawei.com>
Reviewed-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/eventfd.c b/io_uring/eventfd.c
index fab936d31ba8..100d5da94cb9 100644
--- a/io_uring/eventfd.c
+++ b/io_uring/eventfd.c
@@ -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)