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    SubjectRe: [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@linux.vnet.ibm.com>
    Linux Technology Center,
    IBM India Systems and Technology Lab


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