linux-kernel - [PATCH 4/5] cpufreq, policy->initialized count must be atomic

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Message-Id: <1415199239-19019-5-git-send-email-prarit@redhat.com>
Date:	Wed,  5 Nov 2014 09:53:58 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	robert.schoene@...dresden.de, sboyd@...eaurora.org,
	Prarit Bhargava <prarit@...hat.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-pm@...r.kernel.org
Subject: [PATCH 4/5] cpufreq, policy->initialized count must be atomic

The policy->initialized value can be modified from several cpus concurrently if
!CPUFREQ_HAVE_GOVERNOR_PER_POLICY.  This leads to a situation where a
governor maybe switched out even though the governor->initialized is greater
than one.  It must be switched to atomic_t and protected with a mutex to
make sure that future read/writes obtain the correct data.

Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Cc: linux-pm@...r.kernel.org
Signed-off-by: Prarit Bhargava <prarit@...hat.com>
---
 drivers/cpufreq/cpufreq.c          |   12 +++++++++---
 drivers/cpufreq/cpufreq_governor.c |    4 ++--
 include/linux/cpufreq.h            |    3 ++-
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index e33cb15..cf11de6 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2059,10 +2059,12 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
 	ret = policy->governor->governor(policy, event);
 
 	if (!ret) {
+		mutex_lock(&policy->governor->initialized_mutex);
 		if (event == CPUFREQ_GOV_POLICY_INIT)
-			policy->governor->initialized++;
+			atomic_inc(&policy->governor->initialized);
 		else if (event == CPUFREQ_GOV_POLICY_EXIT)
-			policy->governor->initialized--;
+			atomic_dec(&policy->governor->initialized);
+		mutex_unlock(&policy->governor->initialized_mutex);
 	} else {
 		/* Restore original values */
 		mutex_lock(&cpufreq_governor_lock);
@@ -2092,7 +2094,11 @@ int cpufreq_register_governor(struct cpufreq_governor *governor)
 
 	mutex_lock(&cpufreq_governor_mutex);
 
-	governor->initialized = 0;
+	mutex_init(&governor->initialized_mutex);
+	mutex_lock(&governor->initialized_mutex);
+	atomic_set(&governor->initialized, 0);
+	mutex_unlock(&governor->initialized_mutex);
+
 	err = -EBUSY;
 	if (__find_governor(governor->name) == NULL) {
 		err = 0;
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 32ad9db..b1ee597 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -315,7 +315,7 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 					latency * LATENCY_MULTIPLIER));
 
 		if ((cdata->governor == GOV_CONSERVATIVE) &&
-				(!policy->governor->initialized)) {
+		    (!atomic_read(&policy->governor->initialized))) {
 			struct cs_ops *cs_ops = dbs_data->cdata->gov_ops;
 
 			cpufreq_register_notifier(cs_ops->notifier_block,
@@ -336,7 +336,7 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 				cpufreq_put_global_kobject();
 
 			if ((dbs_data->cdata->governor == GOV_CONSERVATIVE) &&
-				(policy->governor->initialized == 1)) {
+			    atomic_read(&policy->governor->initialized) == 1) {
 				struct cs_ops *cs_ops = dbs_data->cdata->gov_ops;
 
 				cpufreq_unregister_notifier(cs_ops->notifier_block,
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 43909ad..73cec45 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -431,7 +431,8 @@ static inline unsigned long cpufreq_scale(unsigned long old, u_int div,
 
 struct cpufreq_governor {
 	char	name[CPUFREQ_NAME_LEN];
-	int	initialized;
+	struct mutex initialized_mutex;
+	atomic_t initialized;
 	int	(*governor)	(struct cpufreq_policy *policy,
 				 unsigned int event);
 	ssize_t	(*show_setspeed)	(struct cpufreq_policy *policy,
-- 
1.7.9.3

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