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Subject[PATCH 4/5] cpufreq, policy->initialized count must be atomic
Date
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@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: linux-pm@vger.kernel.org
Signed-off-by: Prarit Bhargava <prarit@redhat.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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