linux-kernel - Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send

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Message-ID: <5199C990.3020602@linux.vnet.ibm.com>
Date:	Mon, 20 May 2013 14:58:24 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Tejun Heo <tj@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule,
 round 2

On 05/20/2013 02:47 PM, Borislav Petkov wrote:
> On Mon, May 20, 2013 at 02:23:37PM +0800, Michael Wang wrote:
>> On 05/20/2013 12:50 PM, Borislav Petkov wrote:
>>> On Mon, May 20, 2013 at 11:16:33AM +0800, Michael Wang wrote:
>>>> I suppose the reason is that the cpu we passed to
>>>> mod_delayed_work_on() has a chance to become offline before we
>>>> disabled irq, what about check it before send resched ipi? like:
>>>
>>> I think this is only addressing the symptoms - what we should be doing
>>> instead is asking ourselves why are we even scheduling work on a cpu if
>>> the machine goes offline?
>>>
>>> I don't know though who should be responsible for killing all that
>>> work - the workqueue itself or the guy who created it, i.e. cpufreq
>>> governor...
>>
>> So there are two questions here:
>> 1. Is gov_queue_work() want to queue the work on offline cpu?
>> 2. Is mod_delayed_work_on() allow offline cpu?
>>
>> I guess both should be false?
> 
> Well, if we don't allow queueing work on a cpu which goes offline, i.e.
> #2, the problem should be solved.

I've take a look at the usage of queue_delayed_work_on() and
mod_delayed_work_on(), mostly passed this_cpu, or those in online mask,
I think offline cpu is not by designed.

Besides, the cpu gov_queue_work() is using 'policy->cpus' which seems to
be updated during UP DOWN notify, I think they are supposed to be online.

But we need expert in cpufreq to confirm all these...

Regards,
Michael Wang

> 
> Tejun?
> 
> Here are the splats: http://marc.info/?l=linux-kernel&m=136879901425951
> 

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