btrfs: Report error on removing qgroup if del_qgroup_item fails

Previously, we were calling del_qgroup_item, and ignoring the return code
resulting in a potential to have divergent in-memory state without an
error. Perhaps, it makes sense to handle this error code, and put the
filesystem into a read only, or similar state.

This patch only adds reporting of the error if the error is fatal,
(any error other than qgroup not found).
Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Reviewed-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/qgroup.c

@@ -1305,6 +1305,8 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans,
 		}
 	}
 	ret = del_qgroup_item(trans, quota_root, qgroupid);
+	if (ret && ret != -ENOENT)
+		goto out;
 
 	while (!list_empty(&qgroup->groups)) {
 		list = list_first_entry(&qgroup->groups,