PM / hibernate: Fix user space driven resume regression

Recent commit 8fd37a4c (PM / hibernate: Create memory bitmaps after
freezing user space) broke the resume part of the user space driven
hibernation (s2disk), because I forgot that the resume utility
loaded the image into memory without freezing user space (it still
freezes tasks after loading the image).  This means that during user
space driven resume we need to create the memory bitmaps at the
"device open" time rather than at the "freeze tasks" time, so make
that happen (that's a special case anyway, so it needs to be treated
in a special way).
Reported-and-tested-by: Ronald <ronald645@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

kernel/power/snapshot.c

@@ -743,7 +743,10 @@ int create_basic_memory_bitmaps(void)
 	struct memory_bitmap *bm1, *bm2;
 	int error = 0;
 
-	BUG_ON(forbidden_pages_map || free_pages_map);
+	if (forbidden_pages_map && free_pages_map)
+		return 0;
+	else
+		BUG_ON(forbidden_pages_map || free_pages_map);
 
 	bm1 = kzalloc(sizeof(struct memory_bitmap), GFP_KERNEL);
 	if (!bm1)

kernel/power/user.c

@@ -39,6 +39,7 @@ static struct snapshot_data {
 	char frozen;
 	char ready;
 	char platform_support;
+	bool free_bitmaps;
 } snapshot_state;
 
 atomic_t snapshot_device_available = ATOMIC_INIT(1);
@@ -82,6 +83,10 @@ static int snapshot_open(struct inode *inode, struct file *filp)
 		data->swap = -1;
 		data->mode = O_WRONLY;
 		error = pm_notifier_call_chain(PM_RESTORE_PREPARE);
+		if (!error) {
+			error = create_basic_memory_bitmaps();
+			data->free_bitmaps = !error;
+		}
 		if (error)
 			pm_notifier_call_chain(PM_POST_RESTORE);
 	}
@@ -111,6 +116,8 @@ static int snapshot_release(struct inode *inode, struct file *filp)
 		pm_restore_gfp_mask();
 		free_basic_memory_bitmaps();
 		thaw_processes();
+	} else if (data->free_bitmaps) {
+		free_basic_memory_bitmaps();
 	}
 	pm_notifier_call_chain(data->mode == O_RDONLY ?
 			PM_POST_HIBERNATION : PM_POST_RESTORE);
@@ -231,6 +238,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 			break;
 		pm_restore_gfp_mask();
 		free_basic_memory_bitmaps();
+		data->free_bitmaps = false;
 		thaw_processes();
 		data->frozen = 0;
 		break;