Patch "btrfs: don't create or leak aliased root while cleaning up orphans" has been added to the 4.7-stable tree

@@ -1626,8 +1626,8 @@ fail:
 	return ret;
 }
 
-static struct btrfs_root *btrfs_lookup_fs_root(struct btrfs_fs_info *fs_info,
-					       u64 root_id)
+struct btrfs_root *btrfs_lookup_fs_root(struct btrfs_fs_info *fs_info,
+					u64 root_id)
 {
 	struct btrfs_root *root;
 

@@ -68,6 +68,8 @@ struct extent_buffer *btrfs_find_tree_bl
 struct btrfs_root *btrfs_read_fs_root(struct btrfs_root *tree_root,
 				      struct btrfs_key *location);
 int btrfs_init_fs_root(struct btrfs_root *root);
+struct btrfs_root *btrfs_lookup_fs_root(struct btrfs_fs_info *fs_info,
+					u64 root_id);
 int btrfs_insert_fs_root(struct btrfs_fs_info *fs_info,
 			 struct btrfs_root *root);
 void btrfs_free_fs_roots(struct btrfs_fs_info *fs_info);

@@ -272,6 +272,23 @@ int btrfs_find_orphan_roots(struct btrfs
 		root_key.objectid = key.offset;
 		key.offset++;
 
+		/*
+		 * The root might have been inserted already, as before we look
+		 * for orphan roots, log replay might have happened, which
+		 * triggers a transaction commit and qgroup accounting, which
+		 * in turn reads and inserts fs roots while doing backref
+		 * walking.
+		 */
+		root = btrfs_lookup_fs_root(tree_root->fs_info,
+					    root_key.objectid);
+		if (root) {
+			WARN_ON(!test_bit(BTRFS_ROOT_ORPHAN_ITEM_INSERTED,
+					  &root->state));
+			if (btrfs_root_refs(&root->root_item) == 0)
+				btrfs_add_dead_root(root);
+			continue;
+		}
+
 		root = btrfs_read_fs_root(tree_root, &root_key);
 		err = PTR_ERR_OR_ZERO(root);
 		if (err && err != -ENOENT) {

@@ -310,16 +327,8 @@ int btrfs_find_orphan_roots(struct btrfs
 		set_bit(BTRFS_ROOT_ORPHAN_ITEM_INSERTED, &root->state);
 
 		err = btrfs_insert_fs_root(root->fs_info, root);
-		/*
-		 * The root might have been inserted already, as before we look
-		 * for orphan roots, log replay might have happened, which
-		 * triggers a transaction commit and qgroup accounting, which
-		 * in turn reads and inserts fs roots while doing backref
-		 * walking.
-		 */
-		if (err == -EEXIST)
-			err = 0;
 		if (err) {
+			BUG_ON(err == -EEXIST);
 			btrfs_free_fs_root(root);
 			break;
 		}