Btrfs: unlock inodes in correct order in clone ioctl

In the clone ioctl, when the source and target inodes are different,
we can acquire their mutexes in 2 possible different orders. After
we're done cloning, we were releasing the mutexes always in the same
order - the most correct way of doing it is to release them by the
reverse order they were acquired.
Signed-off-by: NFilipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/ioctl.c

@@ -3263,9 +3263,17 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 
 	unlock_extent(&BTRFS_I(src)->io_tree, off, off + len - 1);
 out_unlock:
-	mutex_unlock(&src->i_mutex);
-	if (!same_inode)
-		mutex_unlock(&inode->i_mutex);
+	if (!same_inode) {
+		if (inode < src) {
+			mutex_unlock(&src->i_mutex);
+			mutex_unlock(&inode->i_mutex);
+		} else {
+			mutex_unlock(&inode->i_mutex);
+			mutex_unlock(&src->i_mutex);
+		}
+	} else {
+		mutex_unlock(&src->i_mutex);
+	}
 out_fput:
 	fdput(src_file);
 out_drop_write: