[PATCH V4] cpufreq: governor: Quit work-handlers early if governor is stopped

From: Viresh Kumar
Date: Wed Oct 28 2015 - 22:39:16 EST

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

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

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
@Rafael: Please apply this patch alone for now, let me work out with the
timer/work thing first before applying other patches.

- 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);
- mutex_unlock(&cpufreq_governor_lock);

@@ -229,13 +222,24 @@ static void dbs_timer(struct work_struct *work)
struct cpu_dbs_info *cdbs = container_of(work, struct cpu_dbs_info,
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;


+ 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);


@@ -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;
return 0;

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