1 files changed, 80 insertions, 7 deletions

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index b23a1aac3953..57169f474e4c 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1748,13 +1748,55 @@ out:
 	return ret;
 }
 
-static bool qgroup_has_usage(struct btrfs_qgroup *qgroup)
+/*
+ * Return 0 if we can not delete the qgroup (not empty or has children etc).
+ * Return >0 if we can delete the qgroup.
+ * Return <0 for other errors during tree search.
+ */
+static int can_delete_qgroup(struct btrfs_fs_info *fs_info, struct btrfs_qgroup *qgroup)
 {
-	return (qgroup->rfer > 0 || qgroup->rfer_cmpr > 0 ||
-		qgroup->excl > 0 || qgroup->excl_cmpr > 0 ||
-		qgroup->rsv.values[BTRFS_QGROUP_RSV_DATA] > 0 ||
-		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PREALLOC] > 0 ||
-		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PERTRANS] > 0);
+	struct btrfs_key key;
+	struct btrfs_path *path;
+	int ret;
+
+	/*
+	 * Squota would never be inconsistent, but there can still be case
+	 * where a dropped subvolume still has qgroup numbers, and squota
+	 * relies on such qgroup for future accounting.
+	 *
+	 * So for squota, do not allow dropping any non-zero qgroup.
+	 */
+	if (btrfs_qgroup_mode(fs_info) == BTRFS_QGROUP_MODE_SIMPLE &&
+	    (qgroup->rfer || qgroup->excl || qgroup->excl_cmpr || qgroup->rfer_cmpr))
+		return 0;
+
+	/* For higher level qgroup, we can only delete it if it has no child. */
+	if (btrfs_qgroup_level(qgroup->qgroupid)) {
+		if (!list_empty(&qgroup->members))
+			return 0;
+		return 1;
+	}
+
+	/*
+	 * For level-0 qgroups, we can only delete it if it has no subvolume
+	 * for it.
+	 * This means even a subvolume is unlinked but not yet fully dropped,
+	 * we can not delete the qgroup.
+	 */
+	key.objectid = qgroup->qgroupid;
+	key.type = BTRFS_ROOT_ITEM_KEY;
+	key.offset = -1ULL;
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	ret = btrfs_find_root(fs_info->tree_root, &key, path, NULL, NULL);
+	btrfs_free_path(path);
+	/*
+	 * The @ret from btrfs_find_root() exactly matches our definition for
+	 * the return value, thus can be returned directly.
+	 */
+	return ret;
 }
 
 int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
@@ -1776,7 +1818,10 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 		goto out;
 	}
 
-	if (is_fstree(qgroupid) && qgroup_has_usage(qgroup)) {
+	ret = can_delete_qgroup(fs_info, qgroup);
+	if (ret < 0)
+		goto out;
+	if (ret == 0) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -1801,6 +1846,34 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 	}
 
 	spin_lock(&fs_info->qgroup_lock);
+	/*
+	 * Warn on reserved space. The subvolume should has no child nor
+	 * corresponding subvolume.
+	 * Thus its reserved space should all be zero, no matter if qgroup
+	 * is consistent or the mode.
+	 */
+	WARN_ON(qgroup->rsv.values[BTRFS_QGROUP_RSV_DATA] ||
+		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PREALLOC] ||
+		qgroup->rsv.values[BTRFS_QGROUP_RSV_META_PERTRANS]);
+	/*
+	 * The same for rfer/excl numbers, but that's only if our qgroup is
+	 * consistent and if it's in regular qgroup mode.
+	 * For simple mode it's not as accurate thus we can hit non-zero values
+	 * very frequently.
+	 */
+	if (btrfs_qgroup_mode(fs_info) == BTRFS_QGROUP_MODE_FULL &&
+	    !(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT)) {
+		if (WARN_ON(qgroup->rfer || qgroup->excl ||
+			    qgroup->rfer_cmpr || qgroup->excl_cmpr)) {
+			btrfs_warn_rl(fs_info,
+"to be deleted qgroup %u/%llu has non-zero numbers, rfer %llu rfer_cmpr %llu excl %llu excl_cmpr %llu",
+				      btrfs_qgroup_level(qgroup->qgroupid),
+				      btrfs_qgroup_subvolid(qgroup->qgroupid),
+				      qgroup->rfer, qgroup->rfer_cmpr,
+				      qgroup->excl, qgroup->excl_cmpr);
+			qgroup_mark_inconsistent(fs_info);
+		}
+	}
 	del_qgroup_rb(fs_info, qgroupid);
 	spin_unlock(&fs_info->qgroup_lock);