linux-kernel - Re: x86/mce: machine check warning during poweroff

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Message-ID: <4F18066D.9050102@linux.vnet.ibm.com>
Date:	Thu, 19 Jan 2012 17:32:53 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ming Lei <tom.leiming@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Borislav Petkov <borislav.petkov@....com>,
	Tony Luck <tony.luck@...el.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>,
	gouders@...bocholt.fh-gelsenkirchen.de,
	Marcos Souza <marcos.mage@...il.com>,
	Linux PM mailing list <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	prasad@...ux.vnet.ibm.com, justinmattock@...il.com,
	Jeff Chua <jeff.chua.linux@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>,
	Gilad Ben-Yossef <gilad@...yossef.com>
Subject: Re: x86/mce: machine check warning during poweroff

On 01/19/2012 03:38 AM, Suresh Siddha wrote:

> On Wed, 2012-01-18 at 16:32 +0300, Sergey Senozhatsky wrote:
>> Just a small note, since you're talking about removing CPU from nohz.idle_cpus_mask, 
>> that I'm able to reproduce this problem not only when offlining CPU, but during
>> onlininig as well (kernel 3.3):
> 
> yes, if the nohz state is not cleared properly during offline, then the
> issue can happen any time including cpu online etc.
> 
> Srivatsa, I thought CPU_PRI_SCHED_INACTIVE as INT_MAX for some reason
> and was expecting sched_ilb_notifier() will be called after setting that
> cpu as inactive. I am now using CPU_DYING which will be called from the
> cpu going down.
> 

> Here is the v2 version of the fix. Can you folks please give it another

> try?
> 


Suresh, your patch works perfectly! Thanks a lot!
Tested-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

And the reasoning behind the patch matches the test results:
we don't allow select_nohz_load_balancer() to undo the cleanup that we
did in sched_ilb_notifier(), by ensuring that sched_ilb_notifier() runs
*after* sched_cpu_inactive().

So, you can have my "Reviewed-by" too, if you like!

By the way, it would be great if you could kindly describe the above
mentioned subtle aspect in the patch description as well..

Regards,
Srivatsa S. Bhat

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