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SubjectRe: [PATCH v2 2/3] Mutually exclude cpu online and suspend/hibernate
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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.

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).





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