Re: [PATCH 08/10] io_uring/cancel: drop sqd->lock while SQPOLL waits

[Karl Mehltretter <kmehltretter@gmail.com>]

On Fri, Oct 30, 2026 at 07:34:06AM +0100, Jens Axboe wrote:
> But no reason not to make the check see it. I've queued up the below,
> what do you think? It sets IO_SQ_THREAD_SHOULD_STOP in io_sq_thread()
> before it cancels, and tests that bit in io_sq_offload_create()
> alongside sqd->thread. Then no new state needed.

That looks good, except for the WARN_ON_ONCE() in io_sq_thread_stop()
below.

> diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
> index 49c52284ecdd..c833e776320d 100644
> --- a/io_uring/sqpoll.c
> +++ b/io_uring/sqpoll.c
> @@ -433,6 +433,12 @@ static int io_sq_thread(void *data)
>  	if (io_sq_tw_pending())
>  		io_sq_tw(UINT_MAX);
>  
> +	/*
> +	 * Cancelation drops sqd->lock while it waits, and a ring could attach
> +	 * to a thread that is on its way out. A fatal signal doesn't set the
> +	 * bit, so set it here for io_sq_offload_create() to see.
> +	 */
> +	set_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
>  	io_uring_cancel_generic(true, sqd);

Setting IO_SQ_THREAD_SHOULD_STOP here on a fatal signal means
io_sq_thread_stop() will see it already set when the last ring drops
sqd->refs and trigger:
  
    WARN_ON_ONCE(test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state));

Regards,  
Karl