cpufreq / stats: fix race between stats allocation and first usage

This patch forces complete struct cpufreq_stats allocation for all cpus before
registering CPUFREQ_TRANSITION_NOTIFIER notifier, otherwise in some conditions
cpufreq_stat_notifier_trans() can be called in the middle of stats allocation,
in this case cpufreq_stats_table already exists, but stat->freq_table is NULL.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cpufreq_stats.c

@@ -364,18 +364,21 @@ static int __init cpufreq_stats_init(void)
 	if (ret)
 		return ret;
 
+	register_hotcpu_notifier(&cpufreq_stat_cpu_notifier);
+	for_each_online_cpu(cpu)
+		cpufreq_update_policy(cpu);
+
 	ret = cpufreq_register_notifier(&notifier_trans_block,
 				CPUFREQ_TRANSITION_NOTIFIER);
 	if (ret) {
 		cpufreq_unregister_notifier(&notifier_policy_block,
 				CPUFREQ_POLICY_NOTIFIER);
+		unregister_hotcpu_notifier(&cpufreq_stat_cpu_notifier);
+		for_each_online_cpu(cpu)
+			cpufreq_stats_free_table(cpu);
 		return ret;
 	}
 
-	register_hotcpu_notifier(&cpufreq_stat_cpu_notifier);
-	for_each_online_cpu(cpu) {
-		cpufreq_update_policy(cpu);
-	}
 	return 0;
 }
 static void __exit cpufreq_stats_exit(void)