linux-kernel - Re: [PATCH v2 2/3] Mutually exclude cpu online and suspend/hibernate

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Date:	Mon, 10 Oct 2011 20:46:35 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	rjw@...k.pl, bp@...64.org, pavel@....cz, len.brown@...el.com,
	tj@...nel.org, mingo@...e.hu, akpm@...ux-foundation.org,
	suresh.b.siddha@...el.com, lucas.demarchi@...fusion.mobi,
	rusty@...tcorp.com.au, rdunlap@...otime.net,
	vatsa@...ux.vnet.ibm.com, ashok.raj@...el.com,
	tigran@...azian.fsnet.co.uk, tglx@...utronix.de, hpa@...or.com,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 2/3] Mutually exclude cpu online and suspend/hibernate

On 10/10/2011 07:56 PM, Peter Zijlstra wrote:
> On Mon, 2011-10-10 at 18:15 +0530, Srivatsa S. Bhat wrote:
>>> +     /*
>>> +      * Prevent cpu online and suspend/hibernate (including freezer)
>>> +      * operations from running in parallel. Fail cpu online if suspend or
>>> +      * hibernate has already started.
>>> +      */
>>> +     if (!trylock_pm_sleep())
>>
>> Would it be better to hook into the suspend/hibernate notifiers and
>> use them to exclude cpu hotplug from suspend/hibernate, instead of
>> trying to take pm_mutex lock like this?
>> Peter, I remember you pointing out in another patch's review
>> (http://thread.gmane.org/gmane.linux.kernel/1198312/focus=1199087)
>> that introducing more locks in cpu hotplug would be a bad idea. Does that
>> comment hold here as well, or is this fine? 
> 
> Arguably pm_mutex is already involved in the whole hotplug dance due to
> suspend using it, that said, I'm not at all familiar with the whole
> suspend/hibernate side of things.
> 
> I tried having a quick look this morning but failed to find the actual
> code.
> 
> I think it would be good to have an overview of the various locks and a
> small description of how they interact/nest.
> 

Sure. I'll put together whatever I have understood, in the form of a patch
to Documentation/power directory and post it tomorrow, for the benefit of
all.

> I just remember being very surprised about finding out the hotplug usage
> of suspend/hibernate wasn't at all serialized against the regular
> hotplug thingies.. (see 144060fee07e9c22e179d00819c83c86fbcbf82c).
> 
> 
> 

-- 
Regards,
Srivatsa S. Bhat  <srivatsa.bhat@...ux.vnet.ibm.com>
Linux Technology Center,
IBM India Systems and Technology Lab
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