linux-kernel - RE: [PATCH] io_uring/sqpoll: annotate data race for access in debug check

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Message-ID: <71f1cec18e94459995dfb4bed9a79939@huawei.com>
Date: Wed, 8 Jan 2025 16:24:19 +0000
From: lizetao <lizetao1@...wei.com>
To: Bui Quang Minh <minhquangbui99@...il.com>
CC: Jens Axboe <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com>,
	"io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
	"syzbot+5988142e8a69a67b1418@...kaller.appspotmail.com"
	<syzbot+5988142e8a69a67b1418@...kaller.appspotmail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] io_uring/sqpoll: annotate data race for access in debug
 check

Hi,

> -----Original Message-----
> From: Bui Quang Minh <minhquangbui99@...il.com>
> Sent: Wednesday, January 8, 2025 11:11 PM
> To: linux-kernel@...r.kernel.org
> Cc: Bui Quang Minh <minhquangbui99@...il.com>; Jens Axboe
> <axboe@...nel.dk>; Pavel Begunkov <asml.silence@...il.com>; io-
> uring@...r.kernel.org;
> syzbot+5988142e8a69a67b1418@...kaller.appspotmail.com
> Subject: [PATCH] io_uring/sqpoll: annotate data race for access in debug check
> 
> sqd->thread must only be access while holding sqd->lock. In
> io_sq_thread_stop, the sqd->thread access to wake up the sq thread is placed
> while holding sqd->lock, but the access in debug check is not. As this access if
> for debug check only, we can safely ignore the data race here. So we annotate
> this access with data_race to silence KCSAN.
> 
> Reported-by: syzbot+5988142e8a69a67b1418@...kaller.appspotmail.com
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> ---
>  io_uring/sqpoll.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c index
> 9e5bd79fd2b5..2088c56dbaa0 100644
> --- a/io_uring/sqpoll.c
> +++ b/io_uring/sqpoll.c
> @@ -57,7 +57,7 @@ void io_sq_thread_park(struct io_sq_data *sqd)
> 
>  void io_sq_thread_stop(struct io_sq_data *sqd)  {
> -	WARN_ON_ONCE(sqd->thread == current);
> +	WARN_ON_ONCE(data_race(sqd->thread) == current);
>  	WARN_ON_ONCE(test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd-
> >state));
> 
>  	set_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
> --
> 2.43.0
> 

The modification of this patch itself is fine, but there are two other things I need to confirm.
1、Does the io_uring_cancel_generic() require the same modification?
2、It is not holding sqd->lock in io_req_normal_work_add(), is it safe?

Thanks.
Reviewed-by: Li Zetao<lizetao1@...wei.com>

---
Li Zetao