cgroup: remove css_parent()

cgroup in general is moving towards using cgroup_subsys_state as the
fundamental structural component and css_parent() was introduced to
convert from using cgroup->parent to css->parent.  It was quite some
time ago and we're moving forward with making css more prominent.

This patch drops the trivial wrapper css_parent() and let the users
dereference css->parent.  While at it, explicitly mark fields of css
which are public and immutable.

v2: New usage from device_cgroup.c converted.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: "David S. Miller" <davem@davemloft.net>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Johannes Weiner <hannes@cmpxchg.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0343d7ee6d62..929bbbc539e9 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3176,10 +3176,10 @@ css_next_descendant_pre(struct cgroup_subsys_state *pos,
 
         /* no child, visit my or the closest ancestor's next sibling */
         while (pos != root) {
-                next = css_next_child(pos, css_parent(pos));
+                next = css_next_child(pos, pos->parent);
                 if (next)
                         return next;
-                pos = css_parent(pos);
+                pos = pos->parent;
         }
 
         return NULL;
@@ -3261,12 +3261,12 @@ css_next_descendant_post(struct cgroup_subsys_state *pos,
                 return NULL;
 
         /* if there's an unvisited sibling, visit its leftmost descendant */
-        next = css_next_child(pos, css_parent(pos));
+        next = css_next_child(pos, pos->parent);
         if (next)
                 return css_leftmost_descendant(next);
 
         /* no sibling left, visit parent */
-        return css_parent(pos);
+        return pos->parent;
 }
 
 static bool cgroup_has_live_children(struct cgroup *cgrp)