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Message-Id: <6d6bbd9f1b4d4225555490663b1fee6d39549e70.1455082164.git.viresh.kumar@linaro.org>
Date: Wed, 10 Feb 2016 11:00:25 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Rafael Wysocki <rjw@...ysocki.net>
Cc: linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
Viresh Kumar <viresh.kumar@...aro.org>,
Juri Lelli <juri.lelli@....com>,
Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] cpufreq: governor: Create and traverse list of policy_dbs to fix lockdep
The dbs_data_mutex lock is currently used in two places. First,
cpufreq_governor_dbs() uses it to guarantee mutual exclusion between
invocations of governor operations from the core. Second, it is used by
ondemand governor's update_sampling_rate() to ensure the stability of
data structures walked by it.
The second usage is quite problematic, because update_sampling_rate() is
called from a governor sysfs attribute's ->store callback and that leads
to a deadlock scenario involving cpufreq_governor_exit() which runs
under dbs_data_mutex. Thus it is better to rework the code so
update_sampling_rate() doesn't need to acquire dbs_data_mutex.
To that end, rework update_sampling_rate() to walk a list of policy_dbs
objects supported by the dbs_data one it has been called for (instead of
walking cpu_dbs_info object for all CPUs). The list manipulation is
protected with dbs_data->mutex which also is held around the execution
of update_sampling_rate(), it is not necessary to hold dbs_data_mutex in
that function any more.
Reported-by: Juri Lelli <juri.lelli@....com>
Reported-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
Tested-by: Juri Lelli <juri.lelli@....com>
Tested-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
[ rjw: Changelog ]
---
V5:
- Updated changelog (Thanks again Rafael)
- Fixed bug regarding a-- and --a :)
---
drivers/cpufreq/cpufreq_governor.c | 22 ++++++++--
drivers/cpufreq/cpufreq_governor.h | 7 ++-
drivers/cpufreq/cpufreq_ondemand.c | 89 +++++++++++++-------------------------
3 files changed, 54 insertions(+), 64 deletions(-)
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index bba9d3fb8103..3a9dab752148 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -384,9 +384,14 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy)
ret = -EINVAL;
goto free_policy_dbs_info;
}
- dbs_data->usage_count++;
policy_dbs->dbs_data = dbs_data;
policy->governor_data = policy_dbs;
+
+ mutex_lock(&dbs_data->mutex);
+ dbs_data->usage_count++;
+ list_add(&policy_dbs->list, &dbs_data->policy_dbs_list);
+ mutex_unlock(&dbs_data->mutex);
+
return 0;
}
@@ -396,7 +401,7 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy)
goto free_policy_dbs_info;
}
- dbs_data->usage_count = 1;
+ INIT_LIST_HEAD(&dbs_data->policy_dbs_list);
mutex_init(&dbs_data->mutex);
ret = gov->init(dbs_data, !policy->governor->initialized);
@@ -417,9 +422,12 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy)
if (!have_governor_per_policy())
gov->gdbs_data = dbs_data;
- policy_dbs->dbs_data = dbs_data;
policy->governor_data = policy_dbs;
+ policy_dbs->dbs_data = dbs_data;
+ dbs_data->usage_count = 1;
+ list_add(&policy_dbs->list, &dbs_data->policy_dbs_list);
+
gov->kobj_type.sysfs_ops = &governor_sysfs_ops;
ret = kobject_init_and_add(&dbs_data->kobj, &gov->kobj_type,
get_governor_parent_kobj(policy),
@@ -450,12 +458,18 @@ static int cpufreq_governor_exit(struct cpufreq_policy *policy)
struct dbs_governor *gov = dbs_governor_of(policy);
struct policy_dbs_info *policy_dbs = policy->governor_data;
struct dbs_data *dbs_data = policy_dbs->dbs_data;
+ int count;
/* State should be equivalent to INIT */
if (policy_dbs->policy)
return -EBUSY;
- if (!--dbs_data->usage_count) {
+ mutex_lock(&dbs_data->mutex);
+ list_del(&policy_dbs->list);
+ count = --dbs_data->usage_count;
+ mutex_unlock(&dbs_data->mutex);
+
+ if (!count) {
kobject_put(&dbs_data->kobj);
policy->governor_data = NULL;
diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
index d46ebcb4f16d..4e77efb7db67 100644
--- a/drivers/cpufreq/cpufreq_governor.h
+++ b/drivers/cpufreq/cpufreq_governor.h
@@ -73,7 +73,11 @@ struct dbs_data {
unsigned int up_threshold;
struct kobject kobj;
- /* Protect concurrent updates to governor tunables from sysfs */
+ struct list_head policy_dbs_list;
+ /*
+ * Protect concurrent updates to governor tunables from sysfs,
+ * policy_dbs_list and usage_count.
+ */
struct mutex mutex;
};
@@ -125,6 +129,7 @@ struct policy_dbs_info {
struct work_struct work;
/* dbs_data may be shared between multiple policy objects */
struct dbs_data *dbs_data;
+ struct list_head list;
};
static inline void gov_update_sample_delay(struct policy_dbs_info *policy_dbs,
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index e36792f60348..38301c6b31c7 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -226,84 +226,55 @@ static struct dbs_governor od_dbs_gov;
* @new_rate: new sampling rate
*
* If new rate is smaller than the old, simply updating
- * dbs_tuners_int.sampling_rate might not be appropriate. For example, if the
+ * dbs.sampling_rate might not be appropriate. For example, if the
* original sampling_rate was 1 second and the requested new sampling rate is 10
* ms because the user needs immediate reaction from ondemand governor, but not
* sure if higher frequency will be required or not, then, the governor may
* change the sampling rate too late; up to 1 second later. Thus, if we are
* reducing the sampling rate, we need to make the new value effective
* immediately.
+ *
+ * On the other hand, if new rate is larger than the old, then we may evaluate
+ * the load too soon, and it might we worth updating sample_delay_ns then as
+ * well.
+ *
+ * This must be called with dbs_data->mutex held, otherwise traversing
+ * policy_dbs_list isn't safe.
*/
static void update_sampling_rate(struct dbs_data *dbs_data,
unsigned int new_rate)
{
- struct cpumask cpumask;
- int cpu;
+ struct policy_dbs_info *policy_dbs;
dbs_data->sampling_rate = new_rate = max(new_rate,
dbs_data->min_sampling_rate);
/*
- * Lock governor so that governor start/stop can't execute in parallel.
+ * We are operating under dbs_data->mutex and so the list and its
+ * entries can't be freed concurrently.
*/
- mutex_lock(&dbs_data_mutex);
-
- cpumask_copy(&cpumask, cpu_online_mask);
-
- for_each_cpu(cpu, &cpumask) {
- struct cpufreq_policy *policy;
- struct od_cpu_dbs_info_s *dbs_info;
- struct cpu_dbs_info *cdbs;
- struct policy_dbs_info *policy_dbs;
-
- dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
- cdbs = &dbs_info->cdbs;
- policy_dbs = cdbs->policy_dbs;
-
+ list_for_each_entry(policy_dbs, &dbs_data->policy_dbs_list, list) {
+ mutex_lock(&policy_dbs->timer_mutex);
/*
- * A valid policy_dbs and policy_dbs->policy means governor
- * hasn't stopped or exited yet.
+ * On 32-bit architectures this may race with the
+ * sample_delay_ns read in dbs_update_util_handler(), but that
+ * really doesn't matter. If the read returns a value that's
+ * too big, the sample will be skipped, but the next invocation
+ * of dbs_update_util_handler() (when the update has been
+ * completed) will take a sample. If the returned value is too
+ * small, the sample will be taken immediately, but that isn't a
+ * problem, as we want the new rate to take effect immediately
+ * anyway.
+ *
+ * If this runs in parallel with dbs_work_handler(), we may end
+ * up overwriting the sample_delay_ns value that it has just
+ * written, but the difference should not be too big and it will
+ * be corrected next time a sample is taken, so it shouldn't be
+ * significant.
*/
- if (!policy_dbs || !policy_dbs->policy)
- continue;
-
- policy = policy_dbs->policy;
-
- /* clear all CPUs of this policy */
- cpumask_andnot(&cpumask, &cpumask, policy->cpus);
-
- /*
- * Update sampling rate for CPUs whose policy is governed by
- * dbs_data. In case of governor_per_policy, only a single
- * policy will be governed by dbs_data, otherwise there can be
- * multiple policies that are governed by the same dbs_data.
- */
- if (dbs_data == policy_dbs->dbs_data) {
- mutex_lock(&policy_dbs->timer_mutex);
- /*
- * On 32-bit architectures this may race with the
- * sample_delay_ns read in dbs_update_util_handler(),
- * but that really doesn't matter. If the read returns
- * a value that's too big, the sample will be skipped,
- * but the next invocation of dbs_update_util_handler()
- * (when the update has been completed) will take a
- * sample. If the returned value is too small, the
- * sample will be taken immediately, but that isn't a
- * problem, as we want the new rate to take effect
- * immediately anyway.
- *
- * If this runs in parallel with dbs_work_handler(), we
- * may end up overwriting the sample_delay_ns value that
- * it has just written, but the difference should not be
- * too big and it will be corrected next time a sample
- * is taken, so it shouldn't be significant.
- */
- gov_update_sample_delay(policy_dbs, new_rate);
- mutex_unlock(&policy_dbs->timer_mutex);
- }
+ gov_update_sample_delay(policy_dbs, new_rate);
+ mutex_unlock(&policy_dbs->timer_mutex);
}
-
- mutex_unlock(&dbs_data_mutex);
}
static ssize_t store_sampling_rate(struct dbs_data *dbs_data, const char *buf,
--
2.7.1.370.gb2aa7f8
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