[PATCH 3/4] cgroup: simplify the cgroup descendant helper

[Wei Yang <richard.weiyang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

cgroup_for_each_live_descendant_[pre|post] use cgroup_css() to get the
root. While since the 2nd parameter is NULL, cgroup_css() always return
cgrp->self.

Let's simplify this a little.

Signed-off-by: Wei Yang <richard.weiyang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 kernel/cgroup/cgroup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 570b0c97392a..457353aeb0ca 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -732,7 +732,7 @@ EXPORT_SYMBOL_GPL(of_css);
 
 /* walk live descendants in pre order */
 #define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)		\
-	css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))	\
+	css_for_each_descendant_pre((d_css), &(cgrp)->self)		\
 		if (({ lockdep_assert_held(&cgroup_mutex);		\
 		       (dsct) = (d_css)->cgroup;			\
 		       cgroup_is_dead(dsct); }))			\
@@ -741,7 +741,7 @@ EXPORT_SYMBOL_GPL(of_css);
 
 /* walk live descendants in postorder */
 #define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)		\
-	css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL))	\
+	css_for_each_descendant_post((d_css), &(cgrp)->self)		\
 		if (({ lockdep_assert_held(&cgroup_mutex);		\
 		       (dsct) = (d_css)->cgroup;			\
 		       cgroup_is_dead(dsct); }))			\
-- 
2.23.0