linux-kernel - Re: [PATCH] fix BUG using smp_processor_id() in touch_nmi_watchdog and touch_softlockup

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Date:	Tue, 17 Aug 2010 20:56:56 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Don Zickus <dzickus@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix BUG using smp_processor_id() in touch_nmi_watchdog
 and touch_softlockup_watchdog

On Tue, Aug 17, 2010 at 01:39:48PM +0300, Sergey Senozhatsky wrote:
> Please kindly review.
> 
> ---
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 613bc1f..22dd388 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -116,13 +116,12 @@ static unsigned long get_sample_period(void)
>  static void __touch_watchdog(void)
>  {
>  	int this_cpu = smp_processor_id();
> -
> -	__get_cpu_var(watchdog_touch_ts) = get_timestamp(this_cpu);
> +	per_cpu(watchdog_touch_ts, this_cpu) = get_timestamp(this_cpu);
>  }

The two caller of __touch_watchdog() is:
1)watchdog_timer_fn(): it's preempt disabled when called.
2)watchdog(): it's bound to one cpu. Then means using smp_processor_id()
              safely.

So I think this change is needless, but anyway it's harmless.

Below looks fine to me.
But you still need comments from others.

Thanks,
Yong

>  
>  void touch_softlockup_watchdog(void)
>  {
> -	__get_cpu_var(watchdog_touch_ts) = 0;
> +	__raw_get_cpu_var(watchdog_touch_ts) = 0;
>  }
>  EXPORT_SYMBOL(touch_softlockup_watchdog);
>  
> @@ -142,7 +141,7 @@ void touch_all_softlockup_watchdogs(void)
>  #ifdef CONFIG_HARDLOCKUP_DETECTOR
>  void touch_nmi_watchdog(void)
>  {
> -	__get_cpu_var(watchdog_nmi_touch) = true;
> +	__raw_get_cpu_var(watchdog_nmi_touch) = true;
>  	touch_softlockup_watchdog();
>  }
>  EXPORT_SYMBOL(touch_nmi_watchdog);
--
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