[PATCH] cgroup: Show control files in cgroup2 root after mount

[Waiman Long <longman@redhat.com>]

It was found that when a cgroup2 filesystem was mounted, control
files other than the base cgroup.* ones were not shown in the root
directory.  They were shown only after some controllers were activated
in the root's cgroup.subtree_control file.

This was caused by a lack of the kernfs_activate() call which was fixed
by this patch.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cgroup.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 89a23c6..fb1893b 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2024,8 +2024,10 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
 
 		dentry = cgroup_do_mount(&cgroup2_fs_type, flags, &cgrp_dfl_root,
 					 CGROUP2_SUPER_MAGIC, ns);
-		if (!IS_ERR(dentry))
+		if (!IS_ERR(dentry)) {
 			apply_cgroup_root_flags(root_flags);
+			kernfs_activate(cgrp_dfl_root.cgrp.kn);
+		}
 	} else {
 		dentry = cgroup1_mount(&cgroup_fs_type, flags, data,
 				       CGROUP_SUPER_MAGIC, ns);
-- 
1.8.3.1