From: Tejun Heo <tj@kernel.org>
Date: Tue, 18 Jul 2017 17:57:46 -0400
Subject: [PATCH] cgroup: create dfl_root files on subsys registration
References: bnc#1060662
Patch-mainline: v4.12.6
Git-commit: 7af608e4f9530372aec6e940552bf76595f2e265

commit 7af608e4f9530372aec6e940552bf76595f2e265 upstream.

On subsystem registration, css_populate_dir() is not called on the new
root css, so the interface files for the subsystem on cgrp_dfl_root
aren't created on registration.  This is a residue from the days when
cgrp_dfl_root was used only as the parking spot for unused subsystems,
which no longer is true as it's used as the root for cgroup2.

This is often fine as later operations tend to create them as a part
of mount (cgroup1) or subtree_control operations (cgroup2); however,
it's not difficult to mount cgroup2 with the controller interface
files missing as Waiman found out.

Fix it by invoking css_populate_dir() on the root css on subsys
registration.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 kernel/cgroup/cgroup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 63e2a644baac..916833f51bad 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4578,6 +4578,10 @@ int __init cgroup_init(void)
 
 		if (ss->bind)
 			ss->bind(init_css_set.subsys[ssid]);
+
+		mutex_lock(&cgroup_mutex);
+		css_populate_dir(init_css_set.subsys[ssid]);
+		mutex_unlock(&cgroup_mutex);
 	}
 
 	/* init_css_set.subsys[] has been updated, re-hash */
-- 
2.14.2