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    SubjectRe: [PATCH 0/3] PM: Do not destroy/create devices while suspended
    On Wednesday, 26 of December 2007, Alan Stern wrote:
    > On Tue, 25 Dec 2007, Rafael J. Wysocki wrote:
    > > > > Do we need to worry about the possibility that when the system wakes up
    > > > > from hibernation, the set of usable CPUs might be smaller than it was
    > > > > beforehand?
    > > >
    > > > This is possible in error conditions.
    > > >
    > > > > Is any special handling needed for this, or is it already accounted for?
    > > >
    > > > Hm, well. The cleanest thing would be to allow the drivers to remove the
    > > > device objects on CPU_UP_CANCELED_FROZEN, which means that we weren't able to
    > > > bring the CPU up during a resume, but still that will deadlock with
    > > > gregkh-driver-pm-acquire-device-locks-prior-to-suspending.patch.
    > >
    > > Hmm. In principle, device objects may be destroyed on CPU_UP_CANCELED_FROZEN
    > > without acquiring the device locks, since in fact we know these objects won't
    > > be accessed concurrently at that time (the locks are already held by the PM
    > > core, but the PM core is not going to actually access the devices before the
    > > subsequent resume).
    > How about delaying the CPU_UP_CANCELED_FROZEN announcements until it's
    > really safe to send them out? That is, after all devices have been
    > resumed and the PM core no longer holds any of their locks. (Should
    > this be before or after tasks leave the freezer? -- I'm not sure.)
    > So the idea is send appropriate announcements at the usual time for
    > CPUs that do come back up normally, and don't send anything right away
    > for CPUs that fail to come up. Just keep track of which ones failed,
    > and then later take care of them.

    However, we don't want to execute .resume() for device objects that correspond
    to the "dead" CPUs, so to a minimum we should remove them from the dpm_off
    list on CPU_UP_CANCELED_FROZEN. For this purpose, we can define a
    callback that will remove the device from dpm_off immediately and schedule its
    destruction after all devices have been resumed.


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