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

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Message-ID: <20100816141250.GU4879@redhat.com>
Date:	Mon, 16 Aug 2010 10:12:50 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: fix BUG: using smp_processor_id() in touch_nmi_watchdog and
 touch_softlockup_watchdog

On Mon, Aug 16, 2010 at 03:46:58PM +0200, Peter Zijlstra wrote:
> > I don't see a problem with the patch, but my low level understanding of
> > the __get_cpu_var vs. per_cpu isn't very strong.
> 
> __get_cpu_var() gets you the value on the current cpu, per_cpu() takes a
> cpu argument.

Well I know that much. :-)  It seems that __get_cpu_var depends on
preemption being disabled whereas per_cpu does not?  Though for some
reason I thought __get_cpu_var would be more atomic when it grabbed the
current cpu such that you wouldn't need to disable preemption.  Guess not.

Cheers,
Don

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