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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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