Re: FAILED: patch "[PATCH] io_uring/eventfd: ensure io_eventfd_signal() defers another" failed to apply to 6.12-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 1/12/25 2:16 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.12-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-6.12.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 '2025011244-expedited-clip-fd53@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Here's the 6.12 variant.

-- 
Jens Axboe

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From 5bf17fd4610dd0224652e6aa1d3ead093778ee4d 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

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.

Fixes: 21a091b970cd ("io_uring: signal registered eventfd to process deferred task work")
Reported-by: Jann Horn <jannh@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/eventfd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/io_uring/eventfd.c b/io_uring/eventfd.c
index e37fddd5d9ce..ffc4bd17d078 100644
--- a/io_uring/eventfd.c
+++ b/io_uring/eventfd.c
@@ -38,7 +38,7 @@ static void io_eventfd_do_signal(struct rcu_head *rcu)
 	eventfd_signal_mask(ev_fd->cq_ev_fd, EPOLL_URING_WAKE);
 
 	if (refcount_dec_and_test(&ev_fd->refs))
-		io_eventfd_free(rcu);
+		call_rcu(&ev_fd->rcu, io_eventfd_free);
 }
 
 void io_eventfd_signal(struct io_ring_ctx *ctx)
-- 
2.47.1