linux-kernel - Re: [PATCH v2] watchdog: fix for lockup detector breakage on resume

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Date:	Fri, 8 Jun 2012 14:44:47 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:	Sameer Nanda <snanda@...omium.org>, mingo@...hat.com,
	peterz@...radead.org, len.brown@...el.com, pavel@....cz,
	rjw@...k.pl, dzickus@...hat.com, msb@...omium.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	olofj@...omium.org,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] watchdog: fix for lockup detector breakage on resume

On Mon, 07 May 2012 08:54:57 +0530
Anshuman Khandual <khandual@...ux.vnet.ibm.com> wrote:

> On Tuesday 01 May 2012 10:52 PM, Sameer Nanda wrote:
> 
> > On the suspend/resume path the boot CPU does not go though an
> > offline->online transition.  This breaks the NMI detector
> > post-resume since it depends on PMU state that is lost when
> > the system gets suspended.
> 
> 
> We should not have allowed the PMU to go with events counting on it across the suspend/resume transition
> and find out that the state has been lost. This patch solves the problem of the NMI detector as we restart the
> counter again when the boot cpu comes back online during resume. But the original cause (PMU going with
> counters into the suspend state) which triggered this problem is still there. May be we should have called
> perf_event_exit() on the boot cpu before going into the suspend state. 
> 

That sounds like a nicer solution.

An implementation would be nice ;) I'll keep the original patch on life
support until we get all this nailed down.

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