From: Viresh Kumar <viresh.kumar@linaro.org>
Date: Sat, 31 Aug 2013 12:18:23 +0000 (+0530)
Subject: cpufreq: serialize calls to __cpufreq_governor()
X-Git-Tag: v3.12-rc1~35^2~1^2~8
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=19c763031acb831a5ab9c1a701b7fedda073eb3f;p=pandora-kernel.git

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>
---

Reading git-diff-tree failed