Re: [PATCH 3/3] PM / hibernate / memory hotplug: Rework mutual exclusion

From: Rafael J. Wysocki
Date: Fri Aug 30 2013 - 20:28:48 EST


On Friday, August 30, 2013 06:23:19 PM Toshi Kani wrote:
> On Thu, 2013-08-29 at 23:18 +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >
> > Since all of the memory hotplug operations have to be carried out
> > under device_hotplug_lock, they won't need to acquire pm_mutex if
> > device_hotplug_lock is held around hibernation.
> >
> > For this reason, make the hibernation code acquire
> > device_hotplug_lock after freezing user space processes and
> > release it before thawing them. At the same tim drop the
> > lock_system_sleep() and unlock_system_sleep() calls from
> > lock_memory_hotplug() and unlock_memory_hotplug(), respectively.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > ---
> > kernel/power/hibernate.c | 4 ++++
> > kernel/power/user.c | 2 ++
> > mm/memory_hotplug.c | 4 ----
> > 3 files changed, 6 insertions(+), 4 deletions(-)
> >
> > Index: linux-pm/kernel/power/hibernate.c
> > ===================================================================
> > --- linux-pm.orig/kernel/power/hibernate.c
> > +++ linux-pm/kernel/power/hibernate.c
> > @@ -652,6 +652,7 @@ int hibernate(void)
> > if (error)
> > goto Exit;
> >
> > + lock_device_hotplug();
>
> Since hibernate() can be called from sysfs, do you think the tool may
> see this as a circular dependency with p_active again? This shouldn't
> be a problem in practice, though.

/sys/power/state isn't a device attribute even and is never removed, so it
would be very sad and disappointing if lockdep reported that as a circular
dependency. The deadlock is surely not possible here anyway.

Thanks,
Rafael

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