sysctl,rcu: Convert call_rcu(free_head) to kfree

The RCU callback free_head just calls kfree(), so we can use kfree_rcu()
instead of call_rcu().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

kernel/sysctl.c

@@ -1590,16 +1590,11 @@ void sysctl_head_get(struct ctl_table_header *head)
 	spin_unlock(&sysctl_lock);
 }
 
-static void free_head(struct rcu_head *rcu)
-{
-	kfree(container_of(rcu, struct ctl_table_header, rcu));
-}
-
 void sysctl_head_put(struct ctl_table_header *head)
 {
 	spin_lock(&sysctl_lock);
 	if (!--head->count)
-		call_rcu(&head->rcu, free_head);
+		kfree_rcu(head, rcu);
 	spin_unlock(&sysctl_lock);
 }
 
@@ -1971,10 +1966,10 @@ void unregister_sysctl_table(struct ctl_table_header * header)
 	start_unregistering(header);
 	if (!--header->parent->count) {
 		WARN_ON(1);
-		call_rcu(&header->parent->rcu, free_head);
+		kfree_rcu(header->parent, rcu);
 	}
 	if (!--header->count)
-		call_rcu(&header->rcu, free_head);
+		kfree_rcu(header, rcu);
 	spin_unlock(&sysctl_lock);
 }