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

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Date:	Thu, 17 Mar 2011 12:16:55 +0000 (UTC)
From:	WANG Cong <xiyou.wangcong@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2 v2] watchdog:  Always return NOTIFY_OK during cpu
 up/down events

On Mon, 07 Mar 2011 16:37:40 -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.

What I saw is microcode, its /sys entries failed to come up and this
triggers a warning when these entries are removed when the CPU became 
offline again.

> 
> 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.
> 

Yeah, it should also fix the problem I saw.

Reviewed-by: WANG Cong <xiyou.wangcong@...il.com>

Thanks.

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