cgroup: introduce cgroup_init/exit_cftypes()

Factor out cft->ss initialization into cgroup_init_cftypes() from
cgroup_add_cftypes() and add cft->ss clearing to cgroup_rm_cftypes()
through cgroup_exit_cftypes().

This doesn't make any meaningful difference now but the two new
functions will be expanded during kernfs transition.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

kernel/cgroup.c

@@ -2770,6 +2770,22 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
 	return ret;
 }
 
+static void cgroup_exit_cftypes(struct cftype *cfts)
+{
+	struct cftype *cft;
+
+	for (cft = cfts; cft->name[0] != '\0'; cft++)
+		cft->ss = NULL;
+}
+
+static void cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
+{
+	struct cftype *cft;
+
+	for (cft = cfts; cft->name[0] != '\0'; cft++)
+		cft->ss = ss;
+}
+
 /**
  * cgroup_add_cftypes - add an array of cftypes to a subsystem
  * @ss: target cgroup subsystem
@@ -2787,15 +2803,13 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
 int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
 {
 	struct cftype_set *set;
-	struct cftype *cft;
 	int ret;
 
 	set = kzalloc(sizeof(*set), GFP_KERNEL);
 	if (!set)
 		return -ENOMEM;
 
-	for (cft = cfts; cft->name[0] != '\0'; cft++)
-		cft->ss = ss;
+	cgroup_init_cftypes(ss, cfts);
 
 	cgroup_cfts_prepare();
 	set->cfts = cfts;
@@ -2820,6 +2834,7 @@ EXPORT_SYMBOL_GPL(cgroup_add_cftypes);
  */
 int cgroup_rm_cftypes(struct cftype *cfts)
 {
+	struct cftype *found = NULL;
 	struct cftype_set *set;
 
 	if (!cfts || !cfts[0].ss)
@@ -2831,13 +2846,14 @@ int cgroup_rm_cftypes(struct cftype *cfts)
 		if (set->cfts == cfts) {
 			list_del(&set->node);
 			kfree(set);
-			cgroup_cfts_commit(cfts, false);
-			return 0;
+			found = cfts;
+			break;
 		}
 	}
 
-	cgroup_cfts_commit(NULL, false);
-	return -ENOENT;
+	cgroup_cfts_commit(found, false);
+	cgroup_exit_cftypes(cfts);
+	return found ? 0 : -ENOENT;
 }
 
 /**
@@ -4596,6 +4612,8 @@ int __init cgroup_init(void)
 	if (err)
 		return err;
 
+	cgroup_init_cftypes(NULL, cgroup_base_files);
+
 	for_each_subsys(ss, i) {
 		if (!ss->early_init)
 			cgroup_init_subsys(ss);