btrfs: forbid deleting live subvol qgroup

If a subvolume still exists, forbid deleting its qgroup 0/subvolid.
This behavior generally leads to incorrect behavior in squotas and
doesn't have a legitimate purpose.

Fixes: cecbb533b5fc ("btrfs: record simple quota deltas in delayed refs")
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 63b426cc77989670e0f7890a1cb75a17348e96cb..5470e1cdf10c5348df676cd290bef45811a46019 100644 (file)
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1736,6 +1736,15 @@ out:
        return ret;
 }
 
+static bool qgroup_has_usage(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);
+}
+
 int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 {
        struct btrfs_fs_info *fs_info = trans->fs_info;
@@ -1755,6 +1764,11 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
                goto out;
        }
 
+       if (is_fstree(qgroupid) && qgroup_has_usage(qgroup)) {
+               ret = -EBUSY;
+               goto out;
+       }
+
        /* Check if there are no children of this qgroup */
        if (!list_empty(&qgroup->members)) {
                ret = -EBUSY;