Re: [PATCH V2 7/7] cpufreq: Remove cpufreq_governor_lock

From: Viresh Kumar
Date: Thu Feb 04 2016 - 01:43:15 EST


On 03-02-16, 19:32, Viresh Kumar wrote:
> We used to drop policy->rwsem just before calling __cpufreq_governor()
> in some cases earlier and so it was possible that __cpufreq_governor()
> runs concurrently via separate threads.
>
> In order to guarantee valid state transitions for governors,
> 'governor_enabled' was required to be protected using some locking and
> we created cpufreq_governor_lock for that.
>
> But now, __cpufreq_governor() is always called from within policy->rwsem
> held and so 'governor_enabled' is protected against races even without
> cpufreq_governor_lock.
>
> Get rid of the extra lock now.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
> drivers/cpufreq/cpufreq.c | 7 -------
> 1 file changed, 7 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 4fc3889ca7c9..7bc8a5ed97e5 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -102,7 +102,6 @@ static LIST_HEAD(cpufreq_governor_list);
> static struct cpufreq_driver *cpufreq_driver;
> static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
> static DEFINE_RWLOCK(cpufreq_driver_lock);
> -DEFINE_MUTEX(cpufreq_governor_lock);
>
> /* Flag to suspend/resume CPUFreq governors */
> static bool cpufreq_suspended;
> @@ -1963,11 +1962,9 @@ 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_lock);
> if ((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;
> }
>
> @@ -1976,8 +1973,6 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
> else if (event == CPUFREQ_GOV_START)
> policy->governor_enabled = true;
>
> - mutex_unlock(&cpufreq_governor_lock);
> -
> ret = policy->governor->governor(policy, event);
>
> if (!ret) {
> @@ -1987,12 +1982,10 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
> policy->governor->initialized--;
> } else {
> /* Restore original values */
> - mutex_lock(&cpufreq_governor_lock);
> if (event == CPUFREQ_GOV_STOP)
> policy->governor_enabled = true;
> else if (event == CPUFREQ_GOV_START)
> policy->governor_enabled = false;
> - mutex_unlock(&cpufreq_governor_lock);
> }
>
> if (((event == CPUFREQ_GOV_POLICY_INIT) && ret) ||

+ minor cleanup:

diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
index ed328a39c4ac..7bed63e14e7d 100644
--- a/drivers/cpufreq/cpufreq_governor.h
+++ b/drivers/cpufreq/cpufreq_governor.h
@@ -214,7 +214,6 @@ static inline int delay_for_sampling_rate(unsigned int sampling_rate)
return delay;
}

-extern struct mutex cpufreq_governor_lock;
extern const struct sysfs_ops governor_sysfs_ops;

void gov_add_timers(struct cpufreq_policy *policy, unsigned int delay);

--
viresh