cgroup: make hierarchy iterators deal with cgroup_subsys_state instead of cgroup

cgroup is currently in the process of transitioning to using css
(cgroup_subsys_state) as the primary handle instead of cgroup in
subsystem API.  For hierarchy iterators, this is beneficial because

* In most cases, css is the only thing subsystems care about anyway.

* On the planned unified hierarchy, iterations for different
  subsystems will need to skip over different subtrees of the
  hierarchy depending on which subsystems are enabled on each cgroup.
  Passing around css makes it unnecessary to explicitly specify the
  subsystem in question as css is intersection between cgroup and
  subsystem

* For the planned unified hierarchy, css's would need to be created
  and destroyed dynamically independent from cgroup hierarchy.  Having
  cgroup core manage css iteration makes enforcing deref rules a lot
  easier.

Most subsystem conversions are straight-forward.  Noteworthy changes
are

* blkio: cgroup_to_blkcg() is no longer used.  Removed.

* freezer: cgroup_freezer() is no longer used.  Removed.

* devices: cgroup_to_devcgroup() is no longer used.  Removed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Jens Axboe <axboe@kernel.dk>

1 files changed, 3 insertions, 8 deletions

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index e0ca464fa854..9bf230aa28b0 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -56,11 +56,6 @@ static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
         return s ? container_of(s, struct dev_cgroup, css) : NULL;
 }
 
-static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
-{
-        return css_to_devcgroup(cgroup_css(cgroup, devices_subsys_id));
-}
-
 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
 {
         return css_to_devcgroup(task_css(task, devices_subsys_id));
@@ -447,13 +442,13 @@ static void revalidate_active_exceptions(struct dev_cgroup *devcg)
 static int propagate_exception(struct dev_cgroup *devcg_root,
                                struct dev_exception_item *ex)
 {
-        struct cgroup *root = devcg_root->css.cgroup, *pos;
+        struct cgroup_subsys_state *pos;
         int rc = 0;
 
         rcu_read_lock();
 
-        cgroup_for_each_descendant_pre(pos, root) {
-                struct dev_cgroup *devcg = cgroup_to_devcgroup(pos);
+        css_for_each_descendant_pre(pos, &devcg_root->css) {
+                struct dev_cgroup *devcg = css_to_devcgroup(pos);
 
                 /*
                  * Because devcgroup_mutex is held, no devcg will become