linux-kernel - Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

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Date:	Fri, 12 Nov 2010 10:42:31 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	jason.wessel@...driver.com
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Robert Richter <robert.richter@....com>, ying.huang@...el.com,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

On Fri, Nov 12, 2010 at 09:05:03AM -0600, Jason Wessel wrote:
> On 11/12/2010 08:43 AM, Don Zickus wrote:
> > Restructuring the nmi handler to be more readable and simpler.
> >
> > This is just laying the ground work for future improvements in this area.
> >
> > I also left out one of Huang's patch until we figure out how we are going
> > to proceed with a new notifier.
> >
> > Tested 32-bit and 64-bit on AMD and Intel machines.
> >
> > V2:  add a patch to kill DIE_NMI_IPI and add in priorities
> >
> >   
> 
> Had you tested this code with kgdb boot tests at all?
> 
> CONFIG_LOCKUP_DETECTOR=y
> CONFIG_HARDLOCKUP_DETECTOR=y
> CONFIG_KGDB=y
> CONFIG_KGDB_TESTS_ON_BOOT=y
> CONFIG_KGDB_TESTS_BOOT_STRING="V1F100"
> 
> There has been a regression in kgdb due to the use of perf/NMI in the
> lockup detector ever since the new version has been introduced.   The
> perf callbacks in the lockup detector were consuming NMI events not
> related to the call back and causing the kernel debugger not to work at
> all on SMP systems configured with the lockup detector.

Well 2.6.36 should have fixed that.  Perf was blindly eating all NMI
events if it had a user.  With the new lockup detector, that created a
'user' for perf and it happily ate everything.  But we spent a lot of time
trying to fix that for 2.6.36.  If we missed something, we would like to
know.

To answer your question, I doubt this patch series will change that
outcome if it is still broken.

> 
> I was curious to know if this patch series fixed the problem as well as
> to know if you could run the regression test when you make changes
> related to the lockup / NMI path as it affects the kernel debug API.

Absolutely.  I look forward to running tests with consumers of NMI other
than perf. :-)

Thanks for the tip.

Cheers,
Don
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