linux-kernel - Re: [PATCH 2/2 v2] watchdog: Always return NOTIFY

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Date:	Thu, 17 Mar 2011 10:12:49 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Don Zickus <dzickus@...hat.com>
Cc:	x86@...nel.org, jwjstone@...tmail.fm,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2 v2] watchdog:  Always return NOTIFY_OK during cpu
 up/down events

On Mon, 2011-03-07 at 16:37 -0500, Don Zickus wrote:
> 
> This patch addresses a couple of problems.  One was the case when the
> hardlockup failed to start, it also failed to start the softlockup.
> There were valid cases when the hardlockup shouldn't start and that
> shouldn't block the softlockup (no lapic, bios controls perf
> counters).
> 
> The second problem was when the hardlockup failed to start on boxes
> (from a no lapic or bios controlled perf counter case), it reported
> failure to the cpu notifier chain.  This blocked the notifier from
> continuing to start other more critical pieces of cpu bring-up (in
> our case based on a 2.6.32 fork, it was the mce).  As a result,
> during soft cpu online/offline testing, the system would panic
> when a cpu was offlined because the cpu notifier would succeed in
> processing a watchdog disable cpu event and would panic in the mce
> case as a result of un-initialized variables from a never executed
> cpu up event.
> 
> I realized the hardlockup/softlockup cases are really just debugging
> aids and should never impede the progress of a cpu up/down event.
> Therefore I modified the code to always return NOTIFY_OK and instead
> rely on printks to inform the user of problems.
> 
> Signed-off-by: Don Zickus <dzickus@...hat.com> 

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
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