From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Ming Lei <tom.leiming@gmail.com>,
Djalal Harouni <tixxdz@opendz.org>,
Borislav Petkov <borislav.petkov@amd.com>,
Tony Luck <tony.luck@intel.com>,
Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
Ingo Molnar <mingo@elte.hu>, Andi Kleen <ak@linux.intel.com>,
linux-kernel@vger.kernel.org, Greg Kroah-Hartman <gregkh@suse.de>,
Kay Sievers <kay.sievers@vrfy.org>,
gouders@et.bocholt.fh-gelsenkirchen.de,
Marcos Souza <marcos.mage@gmail.com>,
Linux PM mailing list <linux-pm@vger.kernel.org>,
"Rafael J. Wysocki" <rjw@sisk.pl>,
"tglx@linutronix.de" <tglx@linutronix.de>,
prasad@linux.vnet.ibm.com, justinmattock@gmail.com,
Jeff Chua <jeff.chua.linux@gmail.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Mel Gorman <mgorman@suse.de>,
Gilad Ben-Yossef <gilad@benyossef.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: x86/mce: machine check warning during poweroff
Date: Wed, 18 Jan 2012 18:45:55 +0530 [thread overview]
Message-ID: <4F16C60B.4030903@linux.vnet.ibm.com> (raw)
In-Reply-To: <1326856624.5291.20.camel@sbsiddha-mobl2>
On 01/18/2012 08:47 AM, Suresh Siddha wrote:
> On Tue, 2012-01-17 at 15:22 +0530, Srivatsa S. Bhat wrote:
>> Thanks for the patch, but unfortunately it doesn't fix the problem!
>> Exactly the same stack traces are seen during a CPU Hotplug stress test.
>> (I didn't even have to stress it - it is so fragile that just a script
>> to offline all cpus except the boot cpu was good enough to reproduce the
>> problem easily.)
>
> hmm, that's weird. with the patch, sched_ilb_notifier() should have
> cleared the cpu going offline from the nohz.idle_cpus_mask. And this
> should have happened after that cpu is removed from active mask. So
> no-one else should add that cpu back to the nohz.idle_cpus_mask and this
> should prevent the issue from happening.
>
> I could reproduce the problem easily with out the patch but when I
> applied the patch I couldn't recreate the issue. Srivatsa, can you
> please re-check the kernel you tested indeed has the fix?
>
> re-Reviewing the code/patch also doesn't give me a hint.
>
>> I have a few questions regarding the synchronization with CPU Hotplug.
>> What guarantees that the code which selects and IPIs the new ilb is totally
>> race-free with respect to CPU hotplug and we will never IPI an offline CPU?
>
> So, nohz_balancer_kick() gets called only from interrupts disabled.
> During that time (from selecting the ilb_cpu to sending the IPI), no cpu
> can go offline. As the offline happens from the stop-machine process
> context with interrupts disabled.
>
> Only thing we need to make sure is the offlined cpu shouldn't be part of
> the nohz.idle_cpus_mask and for post 3.2 code, posted patch ensures
> that.
>
> For 3.2 and before, when a cpu exits tickless idle, it gets removed from
> the nohz.idle_cpus_mask (and also from the nohz.load_balancer). And if
> the cpu is not in the active mask (while going offline), subsequent
> calls to select_nohz_load_balancer() ensures that the cpu going down
> doesn't update the nohz structures. So I thought 3.2 shouldn't exhibit
> this problem.
>
>
>> (As demonstrated above, this issue is in 3.2-rc7
>> as well.)
>
> hmm, don't think we ran into this before 3.2. So, what am I missing from
> the above? I will try to reproduce it on 3.2 too.
>
I tested again on 3.2. I didn't hit those warnings (IPI to offline cpus).
It happens only in the post-3.2 kernel.
Regards,
Srivatsa S. Bhat
IBM Linux Technology Center
next prev parent reply other threads:[~2012-01-18 13:16 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-11 0:00 x86/mce: machine check warning during poweroff Djalal Harouni
2012-01-12 14:22 ` Ming Lei
2012-01-13 20:22 ` Srivatsa S. Bhat
2012-01-13 20:34 ` Justin P. Mattock
2012-01-13 20:37 ` Linus Torvalds
2012-01-13 20:53 ` Srivatsa S. Bhat
2012-01-13 21:08 ` Linus Torvalds
2012-01-13 21:24 ` Andi Kleen
2012-01-13 21:38 ` Justin P. Mattock
2012-01-13 22:06 ` Srivatsa S. Bhat
2012-01-13 22:17 ` Alan Stern
2012-01-13 22:18 ` Srivatsa S. Bhat
2012-01-13 23:13 ` Andi Kleen
2012-01-14 0:44 ` Dirk Gouders
2012-01-13 23:02 ` Linus Torvalds
2012-01-13 23:27 ` Srivatsa S. Bhat
2012-01-14 0:05 ` Linus Torvalds
2012-01-14 2:41 ` Srivatsa S. Bhat
2012-01-14 2:53 ` Linus Torvalds
2012-01-14 3:05 ` Srivatsa S. Bhat
2012-01-14 3:10 ` Linus Torvalds
2012-01-14 3:18 ` Srivatsa S. Bhat
2012-01-14 3:41 ` Linus Torvalds
2012-01-14 5:15 ` Tony Luck
2012-01-14 14:49 ` Greg KH
2012-01-14 16:30 ` Alan Stern
2012-01-14 20:45 ` Jeff Chua
2012-01-15 2:05 ` Tony Luck
2012-01-15 2:34 ` Greg KH
2012-01-15 3:36 ` Alan Stern
2012-01-16 18:15 ` Greg KH
2012-01-16 18:11 ` Greg KH
2012-01-16 18:27 ` Luck, Tony
2012-01-16 18:34 ` Greg KH
2012-01-16 18:42 ` Kay Sievers
2012-01-17 2:21 ` Suresh Siddha
2012-01-17 9:52 ` Srivatsa S. Bhat
2012-01-17 16:15 ` Jeff Chua
2012-01-17 16:36 ` Srivatsa S. Bhat
2012-01-18 3:17 ` Suresh Siddha
2012-01-18 10:19 ` Srivatsa S. Bhat
2012-01-18 13:15 ` Srivatsa S. Bhat [this message]
2012-01-18 13:32 ` Sergey Senozhatsky
2012-01-18 22:08 ` Suresh Siddha
2012-01-19 7:50 ` Sergey Senozhatsky
2012-01-19 12:02 ` Srivatsa S. Bhat
2012-01-20 2:28 ` Suresh Siddha
2012-01-23 8:43 ` Peter Zijlstra
2012-01-26 20:27 ` [tip:sched/urgent] sched/nohz: Fix nohz cpu idle load balancing state with cpu hotplug tip-bot for Suresh Siddha
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