cgroup: disallow disabled controllers on the default hierarchy

After booting with cgroup_disable=memory, I still saw memcg files
in the default hierarchy, and I can write to them, though it won't
take effect.

  # dmesg
  ...
  Disabling memory control group subsystem
  ...
  # mount -t cgroup -o __DEVEL__sane_behavior xxx /cgroup
  # ls /cgroup
  ...
  memory.failcnt                   memory.move_charge_at_immigrate
  memory.force_empty               memory.numa_stat
  memory.limit_in_bytes            memory.oom_control
  ...
  # cat /cgroup/memory.usage_in_bytes
  0

tj: Minor comment update.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 9 insertions, 5 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3f46165829a4..3edcc8ae83b5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3069,6 +3069,9 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
 {
         int ret;
 
+        if (ss->disabled)
+                return 0;
+
         if (!cfts || cfts[0].name[0] == '\0')
                 return 0;
 
@@ -4678,8 +4681,6 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
 
         BUG_ON(online_css(css));
 
-        cgrp_dfl_root.subsys_mask |= 1 << ss->id;
-
         mutex_unlock(&cgroup_mutex);
 }
 
@@ -4758,11 +4759,14 @@ int __init cgroup_init(void)
                               &cgrp_dfl_root.cgrp.e_csets[ssid]);
 
                 /*
-                 * cftype registration needs kmalloc and can't be done
-                 * during early_init.  Register base cftypes separately.
+                 * Setting dfl_root subsys_mask needs to consider the
+                 * disabled flag and cftype registration needs kmalloc,
+                 * both of which aren't available during early_init.
                  */
-                if (ss->base_cftypes)
+                if (!ss->disabled) {
+                        cgrp_dfl_root.subsys_mask |= 1 << ss->id;
                         WARN_ON(cgroup_add_cftypes(ss, ss->base_cftypes));
+                }
         }
 
         cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);