linux-kernel - Re: [PATCH 5/5] watchdog: do not unpark threads in watchdog_park

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Date:	Tue, 29 Sep 2015 07:41:51 +0100
From:	Aaron Tomlin <atomlin@...hat.com>
To:	Ulrich Obergfell <uobergfe@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	dzickus@...hat.com
Subject: Re: [PATCH 5/5] watchdog: do not unpark threads in
 watchdog_park_threads() on error

On Mon 2015-09-28 22:44 +0200, Ulrich Obergfell wrote:
> If kthread_park() returns an error, watchdog_park_threads() should not
> blindly 'roll back' the already parked threads to the unparked state.
> Instead leave it up to the callers to handle such errors appropriately
> in their context. For example, it is redundant to unpark the threads
> if the lockup detectors will soon be disabled by the callers anyway.
> 
> Signed-off-by: Ulrich Obergfell <uobergfe@...hat.com>
> ---
>  kernel/watchdog.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 3bc22a9..af70bf2 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -654,6 +654,12 @@ static struct smp_hotplug_thread watchdog_threads = {
>  
>  /*
>   * park all watchdog threads that are specified in 'watchdog_cpumask'
> + *
> + * This function returns an error if kthread_park() of a watchdog thread
> + * fails. In this situation, the watchdog threads of some CPUs can already
> + * be parked and the watchdog threads of other CPUs can still be runnable.
> + * Callers are expected to handle this special condition as appropriate in
> + * their context.
>   */
>  static int watchdog_park_threads(void)
>  {
> @@ -665,10 +671,6 @@ static int watchdog_park_threads(void)
>  		if (ret)
>  			break;
>  	}
> -	if (ret) {
> -		for_each_watchdog_cpu(cpu)
> -			kthread_unpark(per_cpu(softlockup_watchdog, cpu));
> -	}
>  	put_online_cpus();
>  
>  	return ret;

Reviewed-by: Aaron Tomlin <atomlin@...hat.com>

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