ext4: add missing unlock in ext4_check_descriptors() on error path

If there group descriptors are corrupted we need unlock the block
group lock before returning from the function; else we will oops when
freeing a spinlock which is still being held.
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/super.c

@@ -1623,9 +1623,11 @@ static int ext4_check_descriptors(struct super_block *sb)
 			       "Checksum for group %lu failed (%u!=%u)\n",
 			       i, le16_to_cpu(ext4_group_desc_csum(sbi, i,
 			       gdp)), le16_to_cpu(gdp->bg_checksum));
-			if (!(sb->s_flags & MS_RDONLY))
+			if (!(sb->s_flags & MS_RDONLY)) {
+				spin_unlock(sb_bgl_lock(sbi, i));
 				return 0;
 			}
+		}
 		spin_unlock(sb_bgl_lock(sbi, i));
 		if (!flexbg_flag)
 			first_block += EXT4_BLOCKS_PER_GROUP(sb);