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, 1 insertions, 1 deletions

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 371fe8e92ab5..d692b29c083a 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -204,7 +204,7 @@ static inline struct blkcg *bio_blkcg(struct bio *bio)
  */
 static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
 {
-        return css_to_blkcg(css_parent(&blkcg->css));
+        return css_to_blkcg(blkcg->css.parent);
 }
 
 /**