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[RFC PATCH 15/19] cpufreq: remove useless usage of cpufreq_governor_mutex in __cpufreq_governor

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  [RFC PATCH 15/19] cpufreq: remove useless usage of cpufreq_governor_mutex in __cpufreq_governor Juri Lelli <juri.lelli@arm.com> - 2016-01-11 18:40 +0100
    Re: [RFC PATCH 15/19] cpufreq: remove useless usage of  cpufreq_governor_mutex in __cpufreq_governor Viresh Kumar <viresh.kumar@linaro.org> - 2016-01-12 12:10 +0100

#1306556 — [RFC PATCH 15/19] cpufreq: remove useless usage of cpufreq_governor_mutex in __cpufreq_governor

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.

Remove such usage. Also, this cleans up semantic of
cpufreq_governor_mutex: it guards cpufreq_governor_list only.

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
---
 drivers/cpufreq/cpufreq.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index ba452c3..d58a622 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1993,11 +1993,9 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
 
 	pr_debug("%s: for CPU %u, event %u\n", __func__, policy->cpu, event);
 
-	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;
 	}
 
@@ -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

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#1307273 — Re: [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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