Re: [PATCH 0/3] PM: Do not destroy/create devices while suspended

Pavel Machek
2007-12-25T12:35:27Z

On Mon 2007-12-24 10:51:15, Alan Stern wrote:
> On Mon, 24 Dec 2007, Rafael J. Wysocki wrote:
>
> > Hi,
> >
> > Some device drivers register CPU hotplug notifiers and use them to destroy
> > device objects when removing the corresponding CPUs and to create these objects
> > when adding the CPUs back.
> >
> > Unfortunately, this is not the right thing to do during suspend/hibernation,
> > since in that cases the CPU hotplug notifiers are called after suspending
> > devices and before resuming them, so the operations in question are carried
> > out on the objects representing suspended devices which shouldn't be
> > unregistered behing the PM core's back. Although right now it usually doesn't
> > lead to any practical complications, it will predictably deadlock if
> > gregkh-driver-pm-acquire-device-locks-prior-to-suspending.patch is applied.
> >
> > The solution is to prevent drivers from removing/adding devices from within
> > CPU hotplug notifiers during suspend/hibernation using the FROZEN bit
> > in the notifier's action argument. The following three patches modify the
> > MSR, x86-64 MCE and cpuid drivers along these lines.
>
> 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? Is any special handling needed for this, or is it already
> accounted for?

That should not happen... but it does in some error cases.... so
handling it would be a bonus.

Waking up with one cpu out of 8 is bad, but still way better than not
waking up at all ;-).
Pavel
--
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