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Date: Tue, 17 Aug 2010 17:37:34 +0800
Message-ID: <AANLkTikjR1nC3DYdvSw=FEmAVZ98=ju2RNq-MF1L7U3u@mail.gmail.com>
Subject: Re: [PATCH] fix BUG using smp_processor_id() in touch_nmi_watchdog
 and touch_softlockup_watchdog
From: Yong Zhang <yong.zhang0@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>, Don Zickus <dzickus@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
        linux-kernel@vger.kernel.org
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On Tue, Aug 17, 2010 at 5:24 PM, Sergey Senozhatsky
<sergey.senozhatsky@gmail.com> wrote:
> OK. Suppose (I don't know if it could) migration has happen
>
> acpi_os_stall
>        __migration__
>        touch_nmi_watchdog
>
> How calling raw_smp_processor_id() (which is current_thread_info()->cpu)
> vs. preepmt_disable - smp_processor_id() will give us different CPUs?

I don't mean you will get different CPUS(sorry for my poor english).
I mean if the migration could happen, you want to touch_nmi_watchdog()
on CPU A(otherwise the watchdog will shout on us), but eventually we
touch_nmi_watchdog() on CPU B(because of migration),
and this is not what we want.

So preempt_disable() is redundant here.

>
>> So I prefer using __raw_get_cpu_var() as what we have been done before.
>>
>
> Hm...
>
> 26e09c6eee14f4827b55137ba0eedc4e77cd50ab

f69bcf60c3f17aa367e16eef7bc6ab001ea6d58a
2508ce1845a3b256798532b2c6b7997c2dc6533b

you can get the previous touch_*_watchdog there.

Thanks,
Yong
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