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SubjectRe: [RFC PATCH 15/19] cpufreq: remove useless usage of cpufreq_governor_mutex in __cpufreq_governor
On 11-01-16, 17:35, Juri Lelli wrote:
> Commit 6f1e4efd882e ("cpufreq: Fix timer/workqueue corruption by
> protecting reading governor_enabled") made policy->governor_enabled
> guarded by cpufreq_governor_mutex in __cpufreq_governor. Now that
> holding of policy->rwsem is asserted in __cpufreq_governor,
> cpufreq_governor_mutex is overkilling.

I am sure that is going to break it. Try that x86, somehow I don't get
it on my exynos boards.

> - mutex_lock(&cpufreq_governor_mutex);
> if ((policy->governor_enabled && event == CPUFREQ_GOV_START)
> || (!policy->governor_enabled
> && (event == CPUFREQ_GOV_LIMITS || event == CPUFREQ_GOV_STOP))) {
> - mutex_unlock(&cpufreq_governor_mutex);
> return -EBUSY;
> }

Actually the above checks should also be removed as the governors are
responsible for maintaining their state machines. But
userspace/powersave/performance don't have that support yet and so
these checks save them from going into undefined states.

Over that, above and below checks are incomplete..

> @@ -2006,8 +2004,6 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
> else if (event == CPUFREQ_GOV_START)
> policy->governor_enabled = true;
>
> - mutex_unlock(&cpufreq_governor_mutex);
> -
> ret = policy->governor->governor(policy, event);
>
> if (!ret) {
> @@ -2017,12 +2013,10 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
> policy->governor->initialized--;
> } else {
> /* Restore original values */
> - mutex_lock(&cpufreq_governor_mutex);
> if (event == CPUFREQ_GOV_STOP)
> policy->governor_enabled = true;
> else if (event == CPUFREQ_GOV_START)
> policy->governor_enabled = false;
> - mutex_unlock(&cpufreq_governor_mutex);
> }
>
> if (((event == CPUFREQ_GOV_POLICY_INIT) && ret) ||
> --
> 2.2.2

--
viresh

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