linux-kernel - Re: [PATCH] watchdog: ignore nohz

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Date:   Mon, 15 Nov 2021 16:31:48 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Zqiang <qiang.zhang1211@...il.com>
Cc:     akpm@...ux-foundation.org, frederic@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: ignore nohz_full cores in new cpumask

On Fri 2021-11-12 13:14:34, Zqiang wrote:
> If the nohz_full is enabled, when update watchdog_mask, the
> nohz_full cores should be ignored.
> 
> Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
> ---
>  kernel/watchdog.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index ad912511a0c0..3ef11a94783c 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -628,7 +628,9 @@ void lockup_detector_soft_poweroff(void)
>  static void proc_watchdog_update(void)
>  {
>  	/* Remove impossible cpus to keep sysctl output clean. */
> -	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
> +	cpumask_and(&watchdog_cpumask, &watchdog_cpumask,
> housekeeping_cpumask(HK_FLAG_TIMER));

I am not familiar with nozh_full code but this looks fine.


> +	if (cpumask_empty(&watchdog_cpumask))
> +		return;

But this looks looks wrong. Is there any reason for this?

We need to stop the watchdog when it was running before.

I mean that lockup_detector_reconfigure() must be called anytime
when the mask has changed even when it became empty.


>  	lockup_detector_reconfigure();
>  }

Best Regards,
Petr