cgroup: update cgroup->subsys_mask to ->child_subsys_mask and restore cgroup_root->subsys_mask

944196278d3d ("cgroup: move ->subsys_mask from cgroupfs_root to
cgroup") moved ->subsys_mask from cgroup_root to cgroup to prepare for
the unified hierarhcy; however, it turns out that carrying the
subsys_mask of the children in the parent, instead of itself, is a lot
more natural.  This patch restores cgroup_root->subsys_mask and morphs
cgroup->subsys_mask into cgroup->child_subsys_mask.

* Uses of root->cgrp.subsys_mask are restored to root->subsys_mask.

* Remove automatic setting and clearing of cgrp->subsys_mask and
  instead just inherit ->child_subsys_mask from the parent during
  cgroup creation.  Note that this doesn't affect any current
  behaviors.

* Undo __kill_css() separation.

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

1 files changed, 5 insertions, 2 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c2515851c1aa..1b5b2fe1b228 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -173,8 +173,8 @@ struct cgroup {
          */
         u64 serial_nr;
 
-        /* The bitmask of subsystems attached to this cgroup */
-        unsigned long subsys_mask;
+        /* the bitmask of subsystems enabled on the child cgroups */
+        unsigned long child_subsys_mask;
 
         /* Private pointers for each registered subsystem */
         struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
@@ -282,6 +282,9 @@ enum {
 struct cgroup_root {
         struct kernfs_root *kf_root;
 
+        /* The bitmask of subsystems attached to this hierarchy */
+        unsigned long subsys_mask;
+
         /* Unique id for this hierarchy. */
         int hierarchy_id;