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cpufreq: serialize calls to __cpufreq_governor()

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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 <[email protected]>
Signed-off-by: Viresh Kumar <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>
This commit is contained in:
Viresh Kumar 2013-08-31 17:48:23 +05:30 • committed by Rafael J. Wysocki
commit 19c763031a
2 changed files with 7 additions and 1 deletions
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7
drivers/cpufreq/cpufreq.c
View file

@ -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;
}