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 11:39:45 +0300
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Yong Zhang <yong.zhang0@...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

Hello,

On (08/17/10 11:16), Yong Zhang wrote:
> On Tue, Aug 17, 2010 at 10:59 AM, Frederic Weisbecker
> <fweisbec@...il.com> wrote:
> > If preemption is disabled and you deal with the current cpu,
> > then please use __get_cpu_var, it makes the code more
> > readable:
> >
> >
> > void touch_softlockup_watchdog(void)
> > {
> >        preempt_disable();
> >        __(watchdog_touch_ts) = 0;
> >        preempt_enable();
> > }
> 
> Why not use __raw_get_cpu_var() instead?
> You know adding preempt protection in touch_softlockup_watchdog()
> just suppress the warning. Am I missing something?
> 

Sorry, my low level understanding of the __raw_get_cpu_var isn't very strong.
I assume it uses current_thread_info()->cpu in some cases (right?) or 
percpu_from_op.


Should it be
acpi_os_stall
	preepmt_disable
	touch_nmi_watchdog
		touch_softlockup_watchdog
	preempt_enable

?

	Sergey

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