cgroup: make css_tryget_online_from_dir() also recognize cgroup2 fs

The function currently returns -EBADF for a directory on the default
hierarchy.  Make it also recognize cgroup2_fs_type.  This will be used
for perf_event cgroup2 support.
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup.c

@@ -5781,12 +5781,13 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
 						       struct cgroup_subsys *ss)
 {
 	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
+	struct file_system_type *s_type = dentry->d_sb->s_type;
 	struct cgroup_subsys_state *css = NULL;
 	struct cgroup *cgrp;
 
 	/* is @dentry a cgroup dir? */
-	if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
-	    kernfs_type(kn) != KERNFS_DIR)
+	if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
+	    !kn || kernfs_type(kn) != KERNFS_DIR)
 		return ERR_PTR(-EBADF);
 
 	rcu_read_lock();