memcg: add BUILD_BUG_ON() for string tables

Use BUILD_BUG_ON() to compile assert that memcg string tables are in sync
with corresponding enums.  There aren't currently any issues with these
tables.  This is just defensive.
Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -3568,6 +3568,10 @@ static int memcg_stat_show(struct seq_file *m, void *v)
 	struct mem_cgroup *mi;
 	unsigned int i;
 
+	BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_stat_names) !=
+		     MEM_CGROUP_STAT_NSTATS);
+	BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_events_names) !=
+		     MEM_CGROUP_EVENTS_NSTATS);
 	BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_lru_names) != NR_LRU_LISTS);
 
 	for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {