Subject: Re: [PATCH] watchdog: Fix a watchdog crash in some configurations

From: Don Zickus <[email-masked]>
Date: Tue, 5 May 2015 09:35:26 -0400

On Mon, May 04, 2015 at 04:17:07PM -0700, [email-masked] wrote:
> From: John Hubbard <[email-masked]>
> 
> Commit 8fcf2cc768acd845c1fed837bf9cfe2d7106336d in linux-next
> introduced a regression in some configurations. Specifically,
> with CONFIG_NO_HZ_FULL set, and CONFIG_NO_HZ_FULL_ALL *not* set,
> the kernel will crash in lockup_detector_init(), due to a
> NULL tick_nohz_full_mask pointer.
> 
> This is because the above commit uses tick_nohz_full_mask
> (in lockup_detector_init), if CONFIG_NO_HZ_FULL is set, but
> tick_nohz_full_mask only gets allocated if either:
> 
>     a) CONFIG_NO_HZ_FULL_ALL is set, or
> 
>     b) Someone passes in nohz_full=<any_value> on the boot
>       args line.
> 
> To correct this, change lockup_detector_init so that it does
> a runtime check (in addition to the ifdef check). This now
> matches the way most of the other CONFIG_NO_HZ_FULL code does
> it's checking. This fix is a little simpler than my original
> proposed fix, thanks to Chris Metcalf for that.

Hi Chris,

If you are ok with this, I can forward it along.

Cheers,
Don

> 
> Signed-off-by: John Hubbard <[email-masked]>
> ---
>  kernel/watchdog.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 40fda2f..910d73f 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -921,10 +921,14 @@ void __init lockup_detector_init(void)
>  	set_sample_period();
>  
>  #ifdef CONFIG_NO_HZ_FULL
> -	if (!cpumask_empty(tick_nohz_full_mask))
> -		pr_info("Disabling watchdog on nohz_full cores by default\n");
> -	cpumask_andnot(&watchdog_cpumask, cpu_possible_mask,
> -		       tick_nohz_full_mask);
> +	if (tick_nohz_full_enabled()) {
> +		if (!cpumask_empty(tick_nohz_full_mask))
> +			pr_info("Disabling watchdog on nohz_full cores by default\n");
> +		cpumask_andnot(&watchdog_cpumask, cpu_possible_mask,
> +			       tick_nohz_full_mask);
> +	}
> +	else
> +		cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
>  #else
>  	cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
>  #endif
> -- 
> 2.3.7
>