linux-kernel - Re: [PATCH] khungtaskd: Kick stuck processes

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Message-ID: <20180213115642.GR3443@dhcp22.suse.cz>
Date:   Tue, 13 Feb 2018 12:56:42 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Chris Wilson <chris@...is-wilson.co.uk>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] khungtaskd: Kick stuck processes

On Thu 08-02-18 19:07:53, Chris Wilson wrote:
> After spotting a stuck process, and having decided not to panic, give
> the task a kick to see if that helps it to recover (e.g. to paper over a
> missed wake up).

huh, this is just no-no. watchdog is there to report problems not
interfere. You cannot never know whether the sleeper is prepared for
spurious wakeups. Do not paper over bugs...

> References: https://bugs.freedesktop.org/show_bug.cgi?id=104009
> References: https://bugs.freedesktop.org/show_bug.cgi?id=104682
> Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  kernel/hung_task.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 751593ed7c0b..b32acb6bcc63 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -132,6 +132,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
>  		trigger_all_cpu_backtrace();
>  		panic("hung_task: blocked tasks");
>  	}
> +
> +	wake_up_process(t);
>  }
>  
>  /*
> -- 
> 2.16.1

-- 
Michal Hocko
SUSE Labs