Hi,
> -----Original Message-----
> From: Jens Axboe <axboe@xxxxxxxxx>
> Sent: Thursday, January 9, 2025 7:42 AM
> To: io-uring <io-uring@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>
> ---
>
> 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_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)
>
> --
> Jens Axboe
>
>
Tested-by: Li Zetao <lizetao1@xxxxxxxxxx>
Reviewed-by: Li Zetao<lizetao1@xxxxxxxxxx>
---
Li Zetao
