Commit c9a40292 authored Jan 08, 2025 by Jens Axboe

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: 21a091b9 ("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&lt;lizetao1@huawei.com>
Reviewed-by: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 60495b08

io_uring/eventfd.c

+7 −9

Original line number	Diff line number	Diff line
		@@ -33,20 +33,18 @@ static void io_eventfd_free(struct rcu_head *rcu)
		kfree(ev_fd);
		}

		static void io_eventfd_do_signal(struct rcu_head *rcu)
		static void io_eventfd_put(struct io_ev_fd *ev_fd)
		{
		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);
		call_rcu(&ev_fd->rcu, io_eventfd_free);
		}

		static void io_eventfd_put(struct io_ev_fd *ev_fd)
		static void io_eventfd_do_signal(struct rcu_head *rcu)
		{
		if (refcount_dec_and_test(&ev_fd->refs))
		call_rcu(&ev_fd->rcu, io_eventfd_free);
		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);
		io_eventfd_put(ev_fd);
		}

		static void io_eventfd_release(struct io_ev_fd *ev_fd, bool put_ref)