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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 2/3] Mutually exclude cpu online and suspend/hibernate
Date: Tue, 11 Oct 2011 23:56:31 +0200
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Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, bp@amd64.org, pavel@ucw.cz,
        len.brown@intel.com, tj@kernel.org, mingo@elte.hu,
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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