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

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Message-Id: <201110112356.31502.rjw@sisk.pl>
Date:	Tue, 11 Oct 2011 23:56:31 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, 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 Tuesday, October 11, 2011, Srivatsa S. Bhat wrote:
> On 10/10/2011 08:46 PM, Srivatsa S. Bhat wrote:
> > 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.
> > 
> 
> Here it is, just as promised :-)
> http://lkml.org/lkml/2011/10/11/393

Well, I have an idea.

Why don't we make drivers/base/cpu.c:store_online() take pm_mutex
in addition to calling cpu_hotplug_driver_lock()?  This at least
will make the interface mutually exclusive with suspend/hibernation.

Thanks,
Rafael
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