mm: clear N_CPU from node_states at CPU offline

vmstat_cpuup_callback() is a CPU notifier callback, which marks N_CPU to a
node at CPU online event.  However, it does not update this N_CPU info at
CPU offline event.

Changed vmstat_cpuup_callback() to clear N_CPU when the last CPU in the
node is put into offline, i.e.  the node no longer has any online CPU.
Signed-off-by: NToshi Kani <toshi.kani@hp.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Reviewed-by: NYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Tested-by: NYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/vmstat.c

@@ -1229,6 +1229,20 @@ static void start_cpu_timer(int cpu)
 	schedule_delayed_work_on(cpu, work, __round_jiffies_relative(HZ, cpu));
 }
 
+static void vmstat_cpu_dead(int node)
+{
+	int cpu;
+
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		if (cpu_to_node(cpu) == node)
+			goto end;
+
+	node_clear_state(node, N_CPU);
+end:
+	put_online_cpus();
+}
+
 /*
  * Use the cpu notifier to insure that the thresholds are recalculated
  * when necessary.
@@ -1258,6 +1272,7 @@ static int vmstat_cpuup_callback(struct notifier_block *nfb,
 	case CPU_DEAD:
 	case CPU_DEAD_FROZEN:
 		refresh_zone_stat_thresholds();
+		vmstat_cpu_dead(cpu_to_node(cpu));
 		break;
 	default:
 		break;