cpufreq: serialize calls to __cpufreq_governor()

We can't take a big lock around __cpufreq_governor() as this causes
recursive locking for some cases. But calls to this routine must be
serialized for every policy. Otherwise we can see some unpredictable
events.

For example, consider following scenario:

__cpufreq_remove_dev()
 __cpufreq_governor(policy, CPUFREQ_GOV_STOP);
   policy->governor->governor(policy, CPUFREQ_GOV_STOP);
    cpufreq_governor_dbs()
     case CPUFREQ_GOV_STOP:
      mutex_destroy(&cpu_cdbs->timer_mutex)
      cpu_cdbs->cur_policy = NULL;
  <PREEMPT>
store()
 __cpufreq_set_policy()
  __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
    policy->governor->governor(policy, CPUFREQ_GOV_LIMITS);
     case CPUFREQ_GOV_LIMITS:
      mutex_lock(&cpu_cdbs->timer_mutex); <-- Warning (destroyed mutex)
       if (policy->max < cpu_cdbs->cur_policy->cur) <- cur_policy == NULL

And so store() will eventually result in a crash if cur_policy is
NULL at this point.

Introduce an additional variable which would guarantee serialization
here.

Reported-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

2 files changed, 7 insertions, 1 deletions

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 06a2496d2075..7e6baa58a7f2 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1692,13 +1692,15 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
                                                 policy->cpu, event);
 
         mutex_lock(&cpufreq_governor_lock);
-        if ((policy->governor_enabled && event == CPUFREQ_GOV_START)
+        if (policy->governor_busy
+            || (policy->governor_enabled && event == CPUFREQ_GOV_START)
             || (!policy->governor_enabled
             && (event == CPUFREQ_GOV_LIMITS || event == CPUFREQ_GOV_STOP))) {
                 mutex_unlock(&cpufreq_governor_lock);
                 return -EBUSY;
         }
 
+        policy->governor_busy = true;
         if (event == CPUFREQ_GOV_STOP)
                 policy->governor_enabled = false;
         else if (event == CPUFREQ_GOV_START)
@@ -1727,6 +1729,9 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
                         ((event == CPUFREQ_GOV_POLICY_EXIT) && !ret))
                 module_put(policy->governor->owner);
 
+        mutex_lock(&cpufreq_governor_lock);
+        policy->governor_busy = false;
+        mutex_unlock(&cpufreq_governor_lock);
         return ret;
 }
 
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index d568f3975eeb..cca885dac1d3 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -76,6 +76,7 @@ struct cpufreq_policy {
         struct cpufreq_governor *governor; /* see below */
         void                    *governor_data;
         bool                    governor_enabled; /* governor start/stop flag */
+        bool                    governor_busy;
 
         struct work_struct      update; /* if update_policy() needs to be
                                          * called, but you're in IRQ context */