mm: set N_CPU to node_states during boot

After a system booted, N_CPU is not set to any node as has_cpu shows an
empty line.

  # cat /sys/devices/system/node/has_cpu
  (show-empty-line)

setup_vmstat() registers its CPU notifier callback,
vmstat_cpuup_callback(), which marks N_CPU to a node when a CPU is put
into online.  However, setup_vmstat() is called after all CPUs are
launched in the boot sequence.

Changed setup_vmstat() to mark N_CPU to the nodes with online CPUs at
boot, which is consistent with other operations in
vmstat_cpuup_callback(), i.e.  start_cpu_timer() and
refresh_zone_stat_thresholds().

Also added get_online_cpus() to protect the for_each_online_cpu() loop.
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

@@ -1276,8 +1276,12 @@ static int __init setup_vmstat(void)
 
 	register_cpu_notifier(&vmstat_notifier);
 
-	for_each_online_cpu(cpu)
+	get_online_cpus();
+	for_each_online_cpu(cpu) {
 		start_cpu_timer(cpu);
+		node_set_state(cpu_to_node(cpu), N_CPU);
+	}
+	put_online_cpus();
 #endif
 #ifdef CONFIG_PROC_FS
 	proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations);