linux-kernel - [PATCH v2] cpufreq: stats: Walk online CPUs with CPU offline/online locked

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Message-ID: <2278154.xyiFOocWfq@vostro.rjw.lan>
Date:	Fri, 20 May 2016 03:41:32 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Linux PM list <linux-pm@...r.kernel.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: [PATCH v2] cpufreq: stats: Walk online CPUs with CPU offline/online locked

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Loops over online CPUs in cpufreq_stats_init() and cpufreq_stats_exit()
should be carried out with CPU offline/online locked or races are
possible otherwise, so make that happen.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---

v1 -> v2: On a second thought, add the policy notifier in cpufreq_stats_init()
  with CPU offline/online locked too.

---
 drivers/cpufreq/cpufreq_stats.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/cpufreq/cpufreq_stats.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq_stats.c
+++ linux-pm/drivers/cpufreq/cpufreq_stats.c
@@ -317,10 +317,13 @@ static int __init cpufreq_stats_init(voi
 	unsigned int cpu;
 
 	spin_lock_init(&cpufreq_stats_lock);
+
+	get_online_cpus();
+
 	ret = cpufreq_register_notifier(&notifier_policy_block,
 				CPUFREQ_POLICY_NOTIFIER);
 	if (ret)
-		return ret;
+		goto out;
 
 	for_each_online_cpu(cpu)
 		cpufreq_stats_create_table(cpu);
@@ -332,21 +335,28 @@ static int __init cpufreq_stats_init(voi
 				CPUFREQ_POLICY_NOTIFIER);
 		for_each_online_cpu(cpu)
 			cpufreq_stats_free_table(cpu);
-		return ret;
 	}
 
-	return 0;
+ out:
+	put_online_cpus();
+
+	return ret;
 }
 static void __exit cpufreq_stats_exit(void)
 {
 	unsigned int cpu;
 
+	get_online_cpus();
+
 	cpufreq_unregister_notifier(&notifier_policy_block,
 			CPUFREQ_POLICY_NOTIFIER);
 	cpufreq_unregister_notifier(&notifier_trans_block,
 			CPUFREQ_TRANSITION_NOTIFIER);
+
 	for_each_online_cpu(cpu)
 		cpufreq_stats_free_table(cpu);
+
+	put_online_cpus();
 }
 
 MODULE_AUTHOR("Zou Nan hai <nanhai.zou@...el.com>");