Re: [PATCH 0/4] PM: Do not destroy/create devices while suspended (rev. 2)

Ingo Molnar
2008-01-02T10:53:08Z

* Rafael J. Wysocki <rjw@sisk.pl> 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. However, this has to be
> done with care, since the devices objects related to the nonboot CPUs
> that failed to go online during resume should not be present in the
> system. For this reason, it seems reasonable to introduce a mechanism
> allowing drivers to ask the PM core to remove device objects
> corresponding to suspended devices on their behalf.
>
> The first patch in the series introduces such a mechanism. The
> remaining three patches modify the MSR, x86-64 MCE and cpuid drivers
> in accordance with the above approach.

btw., it would be really, really cool if there was a scriptable way i
could test suspend/resume functionality. Pavel has this /dev/rtc thing
to set up an alarm (not sure how functional it is) - would it be
possible to have it as a "suspend for 10 seconds then resume" debug
functionality? That way any suspend breakage would be detectable (and
bisectable) in automated testing - if the resume does not come back
after 10-20 seconds then the test failed.

Ingo
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