Move grabbing s_umount to callers of grab_super()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/block_dev.c

@@ -245,6 +245,7 @@ struct super_block *freeze_bdev(struct block_device *bdev)
 	sb = get_active_super(bdev);
 	if (!sb)
 		goto out;
+	down_write(&sb->s_umount);
 	if (sb->s_flags & MS_RDONLY) {
 		sb->s_frozen = SB_FREEZE_TRANS;
 		up_write(&sb->s_umount);

fs/super.c

@@ -210,7 +210,6 @@ static int grab_super(struct super_block *s) __releases(sb_lock)
 {
 	if (atomic_inc_not_zero(&s->s_active)) {
 		spin_unlock(&sb_lock);
-		down_write(&s->s_umount);
 		return 1;
 	}
 	/* it's going away */
@@ -317,6 +316,7 @@ struct super_block *sget(struct file_system_type *type,
 				up_write(&s->s_umount);
 				destroy_super(s);
 			}
+			down_write(&old->s_umount);
 			return old;
 		}
 	}
@@ -466,7 +466,7 @@ EXPORT_SYMBOL(get_super);
  *
  * Scans the superblock list and finds the superblock of the file system
  * mounted on the device given.  Returns the superblock with an active
- * reference and s_umount held exclusively or %NULL if none was found.
+ * reference or %NULL if none was found.
  */
 struct super_block *get_active_super(struct block_device *bdev)
 {