Re: [PATCH] io_uring: consistently use rcu semantics with sqpoll thread

[Keith Busch <kbusch@kernel.org>]

On Tue, Jun 10, 2025 at 02:52:28PM -0600, Jens Axboe wrote:
> Ah we can probably get by with just a bit more work, something like
> this per section should do it.

Nice, and it clears up the data_race() usage with the assignment and
access both under the sqd mutex.
 
> diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
> index 0625a421626f..8852e104ed68 100644
> --- a/io_uring/sqpoll.c
> +++ b/io_uring/sqpoll.c
> @@ -46,13 +46,18 @@ void io_sq_thread_unpark(struct io_sq_data *sqd)
>  void io_sq_thread_park(struct io_sq_data *sqd)
>  	__acquires(&sqd->lock)
>  {
> -	WARN_ON_ONCE(data_race(sqd->thread) == current);
> +	struct task_struct *tsk;
>  
>  	atomic_inc(&sqd->park_pending);
>  	set_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
>  	mutex_lock(&sqd->lock);
> -	if (sqd->thread)
> -		wake_up_process(sqd->thread);
> +	rcu_read_lock();
> +	tsk = rcu_dereference(sqd->thread);
> +	if (tsk) {
> +		WARN_ON_ONCE(tsk == current);
> +		wake_up_process(tsk);
> +	}
> +	rcu_read_unlock();
>  }
>  
>  void io_sq_thread_stop(struct io_sq_data *sqd)
> 
> -- 
> Jens Axboe