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 --- @Rafael: Please apply this patch alone for now, let me work out with the timer/work thing first before applying other patches.
V3->V4: - Updated changelog as suggested by Rafael.
drivers/cpufreq/cpufreq_governor.c | 33 +++++++++++++++++++++++---------- 1 file changed, 23 insertions(+), 10 deletions(-)
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index 11258c4c1b17..b260576ddb12 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -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; }