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 Zetaolizetao1@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)