cgroup: allow dumping non-criu cgsets that don't match the root

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/cgroup.c

@@ -519,6 +519,10 @@ static int add_cgroup(const char *fpath, const struct stat *sb, int typeflag)
 		mtype = find_dir(ncd->path, &current_controller->heads, &match);
 
 		switch (mtype) {
+		/* ignore co-mounted cgroups and already dumped cgroups */
+		case EXACT_MATCH:
+			exit_code = 0;
+			goto out;
 		case PARENT_MATCH:
 			list_add_tail(&ncd->siblings, &match->children);
 			match->n_children++;
@@ -527,8 +531,6 @@ static int add_cgroup(const char *fpath, const struct stat *sb, int typeflag)
 			list_add_tail(&ncd->siblings, &current_controller->heads);
 			current_controller->n_heads++;
 			break;
-		/* the same hierarchy won't be walked twice for a single process */
-		case EXACT_MATCH:
 		default:
 			BUG();
 		}
@@ -698,6 +700,10 @@ int dump_task_cgroup(struct pstree_item *item, u32 *cg_id, struct parasite_dump_
 		 */
 		if (cs != criu_cgset && collect_cgroups(&cs->ctls))
 			return -1;
+	} else {
+		pr_info("Set %d is a stray\n", cs->id);
+		if (collect_cgroups(&cs->ctls))
+			return -1;
 	}
 
 	*cg_id = cs->id;
@@ -915,18 +921,10 @@ int dump_cgroups(void)
 
 	/*
 	 * Check whether root task lives in its own set as compared
-	 * to criu. If yes, we should not dump anything, but make
-	 * sure no other sets exist. The latter case can be supported,
-	 * but requires some trickery and is hardly needed at the
-	 * moment.
+	 * to criu. If yes, we should not dump anything.
 	 */
 
-	if (root_cgset == criu_cgset) {
-		if (!list_is_singular(&cg_sets)) {
-			pr_err("Non supported sub-cgroups found\n");
-			return -1;
-		}
-
+	if (root_cgset == criu_cgset && list_is_singular(&cg_sets)) {
 		pr_info("All tasks in criu's cgroups. Nothing to dump.\n");
 		return 0;
 	}