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Subject[PATCH 3/5] cpufreq, dbs_data->usage count must be atomic
Date
The usage_count value can be modified from several cpus concurrently if
!CPUFREQ_HAVE_GOVERNOR_PER_POLICY. This leads to a variety of panics in
which the usage_count is negative or exceeds the number of cpus in the
system. 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_governor.c | 16 ++++++++++++----
drivers/cpufreq/cpufreq_governor.h | 3 ++-
2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 1b44496..32ad9db 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -265,7 +265,9 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
if (have_governor_per_policy()) {
WARN_ON(dbs_data);
} else if (dbs_data) {
- dbs_data->usage_count++;
+ mutex_lock(&dbs_data->usage_count_mutex);
+ atomic_inc(&dbs_data->usage_count);
+ mutex_unlock(&dbs_data->usage_count_mutex);
policy->governor_data = dbs_data;
return 0;
}
@@ -277,7 +279,10 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
}

dbs_data->cdata = cdata;
- dbs_data->usage_count = 1;
+ mutex_init(&dbs_data->usage_count_mutex);
+ mutex_lock(&dbs_data->usage_count_mutex);
+ atomic_set(&dbs_data->usage_count, 1);
+ mutex_unlock(&dbs_data->usage_count_mutex);
rc = cdata->init(dbs_data);
if (rc) {
pr_err("%s: POLICY_INIT: init() failed\n", __func__);
@@ -322,7 +327,8 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,

return 0;
case CPUFREQ_GOV_POLICY_EXIT:
- if (!--dbs_data->usage_count) {
+ mutex_lock(&dbs_data->usage_count_mutex);
+ if (atomic_dec_and_test(&dbs_data->usage_count)) {
sysfs_remove_group(get_governor_parent_kobj(policy),
get_sysfs_attr(dbs_data));

@@ -338,9 +344,11 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
}

cdata->exit(dbs_data);
+ mutex_unlock(&dbs_data->usage_count_mutex);
kfree(dbs_data);
cdata->gdbs_data = NULL;
- }
+ } else
+ mutex_unlock(&dbs_data->usage_count_mutex);

policy->governor_data = NULL;
return 0;
diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
index cc401d1..53ca449 100644
--- a/drivers/cpufreq/cpufreq_governor.h
+++ b/drivers/cpufreq/cpufreq_governor.h
@@ -219,7 +219,8 @@ struct common_dbs_data {
struct dbs_data {
struct common_dbs_data *cdata;
unsigned int min_sampling_rate;
- int usage_count;
+ struct mutex usage_count_mutex;
+ atomic_t usage_count;
void *tuners;

/* dbs_mutex protects dbs_enable in governor start/stop */
--
1.7.9.3


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