netdev - Re: [PATCH net] net: linkwatch: use system_unbound

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Message-ID: <20240805175455.69545-1-kuniyu@amazon.com>
Date: Mon, 5 Aug 2024 10:54:55 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <eric.dumazet@...il.com>, <kuba@...nel.org>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>, <syzkaller@...glegroups.com>,
	<kuniyu@...zon.com>
Subject: Re: [PATCH net] net: linkwatch: use system_unbound_wq

From: Eric Dumazet <edumazet@...gle.com>
Date: Mon,  5 Aug 2024 08:58:21 +0000
> linkwatch_event() grabs possibly very contended RTNL mutex.
> 
> system_wq is not suitable for such work.
> 
> Inspired by many noisy syzbot reports.
> 
> 3 locks held by kworker/0:7/5266:
>  #0: ffff888015480948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3206 [inline]
>  #0: ffff888015480948 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x90a/0x1830 kernel/workqueue.c:3312
>  #1: ffffc90003f6fd00 ((linkwatch_work).work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3207 [inline]
>  , at: process_scheduled_works+0x945/0x1830 kernel/workqueue.c:3312
>  #2: ffffffff8fa6f208 (rtnl_mutex){+.+.}-{3:3}, at: linkwatch_event+0xe/0x60 net/core/link_watch.c:276
> 
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>


> ---
>  net/core/link_watch.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/link_watch.c b/net/core/link_watch.c
> index 8ec35194bfcb8574f53a9fd28f0cb2ebfe9a3f2e..ab150641142aa1545c71fc5d3b11db33c70cf437 100644
> --- a/net/core/link_watch.c
> +++ b/net/core/link_watch.c
> @@ -148,9 +148,9 @@ static void linkwatch_schedule_work(int urgent)
>  	 * override the existing timer.
>  	 */
>  	if (test_bit(LW_URGENT, &linkwatch_flags))
> -		mod_delayed_work(system_wq, &linkwatch_work, 0);
> +		mod_delayed_work(system_unbound_wq, &linkwatch_work, 0);
>  	else
> -		schedule_delayed_work(&linkwatch_work, delay);
> +		queue_delayed_work(system_unbound_wq, &linkwatch_work, delay);
>  }
>  
>  
> -- 
> 2.46.0.rc2.264.g509ed76dc8-goog