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

[Toshi Kani <toshi.kani@hp.com>]

On Thu, 2013-08-29 at 23:18 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> 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@intel.com>
> ---
>  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.

Thanks,
-Toshi

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