unsigned long val = 0;
int cpu;
+ get_online_cpus();
for_each_online_cpu(cpu)
val += per_cpu(memcg->stat->events[idx], cpu);
#ifdef CONFIG_HOTPLUG_CPU
val += memcg->nocpu_base.events[idx];
spin_unlock(&memcg->pcp_counter_lock);
#endif
+ put_online_cpus();
return val;
}