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>

kernel/power/hibernate.c

@@ -652,6 +652,7 @@ int hibernate(void)
 	if (error)
 		goto Exit;
 
+	lock_device_hotplug();
 	/* Allocate memory management structures */
 	error = create_basic_memory_bitmaps();
 	if (error)
@@ -685,6 +686,7 @@ int hibernate(void)
  Free_bitmaps:
 	free_basic_memory_bitmaps();
  Thaw:
+	unlock_device_hotplug();
 	thaw_processes();
 
 	/* Don't bother checking whether freezer_test_done is true */
@@ -814,6 +816,7 @@ static int software_resume(void)
 
 	pr_debug("PM: Loading hibernation image.\n");
 
+	lock_device_hotplug();
 	error = create_basic_memory_bitmaps();
 	if (error)
 		goto Thaw;
@@ -827,6 +830,7 @@ static int software_resume(void)
 	swsusp_free();
 	free_basic_memory_bitmaps();
  Thaw:
+	unlock_device_hotplug();
 	thaw_processes();
  Finish:
 	pm_notifier_call_chain(PM_POST_RESTORE);

kernel/power/user.c

@@ -201,6 +201,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 	if (!mutex_trylock(&pm_mutex))
 		return -EBUSY;
 
+	lock_device_hotplug();
 	data = filp->private_data;
 
 	switch (cmd) {
@@ -373,6 +374,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 
 	}
 
+	unlock_device_hotplug();
 	mutex_unlock(&pm_mutex);
 
 	return error;

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);
 }