Revert "cgroup: Move rcu_head up near the top of cgroup_root"

This reverts commit f3c60ab which is
commit a7fb042 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I9cd2b0e4ad7ee33ab44d195935094c7d5855f8ae
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: gregkh

include/linux/cgroup-defs.h

@@ -560,10 +560,6 @@ struct cgroup_root {
 	/* Unique id for this hierarchy. */
 	int hierarchy_id;
 
-	/* A list running through the active hierarchies */
-	struct list_head root_list;
-	struct rcu_head rcu;	/* Must be near the top */
-
 	/*
 	 * The root cgroup. The containing cgroup_root will be destroyed on its
 	 * release. cgrp->ancestors[0] will be used overflowing into the
@@ -577,6 +573,10 @@ struct cgroup_root {
 	/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
 	atomic_t nr_cgrps;
 
+	/* A list running through the active hierarchies */
+	struct list_head root_list;
+	struct rcu_head rcu;
+
 	/* Hierarchy-specific flags */
 	unsigned int flags;