ext4: add ext4_mb_unload_buddy in the error path

commit 02b78310 upstream.

ext4_free_blocks fails to pair an ext4_mb_load_buddy with a matching
ext4_mb_unload_buddy when it fails a memory allocation.
Signed-off-by: Salman Qazi <sqazi@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/ext4/mballoc.c

@@ -4693,6 +4693,7 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 		 */
 		new_entry = kmem_cache_alloc(ext4_free_ext_cachep, GFP_NOFS);
 		if (!new_entry) {
+			ext4_mb_unload_buddy(&e4b);
 			err = -ENOMEM;
 			goto error_return;
 		}