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cpufreq: governor: Quit work-handlers early if governor is stopped

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gov_queue_work() acquires cpufreq_governor_lock to allow
cpufreq_governor_stop() to drain delayed work items possibly scheduled
on CPUs that share the policy with a CPU being taken offline.

However, the same goal may be achieved in a more straightforward way if
the policy pointer in the struct cpu_dbs_info matching the policy CPU is
reset upfront by cpufreq_governor_stop() under the timer_mutex belonging
to it and checked against NULL, under the same lock, at the beginning of
dbs_timer().

In that case every instance of dbs_timer() run for a struct cpu_dbs_info
sharing the policy pointer in question after cpufreq_governor_stop() has
started will notice that that pointer is NULL and bail out immediately
without queuing up any new work items.  In turn, gov_cancel_work()
called by cpufreq_governor_stop() before destroying timer_mutex will
wait for all of the delayed work items currently running on the CPUs
sharing the policy to drop the mutex, so it may be destroyed safely.

Make cpufreq_governor_stop() and dbs_timer() work as described and
modify gov_queue_work() so it does not acquire cpufreq_governor_lock any
more.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Viresh Kumar 2015-10-29 08:08:38 +05:30 committed by Rafael J. Wysocki
parent 539342f60b
commit 3a91b069ea
1 changed files with 23 additions and 10 deletions
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33
drivers/cpufreq/cpufreq_governor.c
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@ -171,10 +171,6 @@ void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
{
int i;
mutex_lock(&cpufreq_governor_lock);
if (!policy->governor_enabled)
goto out_unlock;
if (!all_cpus) {
/*
* Use raw_smp_processor_id() to avoid preemptible warnings.
@ -188,9 +184,6 @@ void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
for_each_cpu(i, policy->cpus)
__gov_queue_work(i, dbs_data, delay);
}
out_unlock:
mutex_unlock(&cpufreq_governor_lock);
}
EXPORT_SYMBOL_GPL(gov_queue_work);
@ -229,13 +222,24 @@ static void dbs_timer(struct work_struct *work)
struct cpu_dbs_info *cdbs = container_of(work, struct cpu_dbs_info,
dwork.work);
struct cpu_common_dbs_info *shared = cdbs->shared;
struct cpufreq_policy *policy = shared->policy;
struct dbs_data *dbs_data = policy->governor_data;
struct cpufreq_policy *policy;
struct dbs_data *dbs_data;
unsigned int sampling_rate, delay;
bool modify_all = true;
mutex_lock(&shared->timer_mutex);
policy = shared->policy;
/*
* Governor might already be disabled and there is no point continuing
* with the work-handler.
*/
if (!policy)
goto unlock;
dbs_data = policy->governor_data;
if (dbs_data->cdata->governor == GOV_CONSERVATIVE) {
struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
@ -252,6 +256,7 @@ static void dbs_timer(struct work_struct *work)
delay = dbs_data->cdata->gov_dbs_timer(cdbs, dbs_data, modify_all);
gov_queue_work(dbs_data, policy, delay, modify_all);
unlock:
mutex_unlock(&shared->timer_mutex);
}
@ -478,9 +483,17 @@ static int cpufreq_governor_stop(struct cpufreq_policy *policy,
if (!shared || !shared->policy)
return -EBUSY;
/*
* Work-handler must see this updated, as it should not proceed any
* further after governor is disabled. And so timer_mutex is taken while
* updating this value.
*/
mutex_lock(&shared->timer_mutex);
shared->policy = NULL;
mutex_unlock(&shared->timer_mutex);
gov_cancel_work(dbs_data, policy);
shared->policy = NULL;
mutex_destroy(&shared->timer_mutex);
return 0;
}