PM / hibernate / memory hotplug: Rework mutual exclusion

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>
Acked-by: Toshi Kani <toshi.kani@hp.com>

mm/memory_hotplug.c

@@ -51,14 +51,10 @@ DEFINE_MUTEX(mem_hotplug_mutex);
 void lock_memory_hotplug(void)
 {
 	mutex_lock(&mem_hotplug_mutex);
-
-	/* for exclusive hibernation if CONFIG_HIBERNATION=y */
-	lock_system_sleep();
 }
 
 void unlock_memory_hotplug(void)
 {
-	unlock_system_sleep();
 	mutex_unlock(&mem_hotplug_mutex);
 }