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Subject[patch 1/4] cpufreq: Eliminate the recent lockdep warnings in cpufreq
Commit b14893a62c73af0eca414cfed505b8c09efc613c although it was very
much needed to properly cleanup ondemand timer, opened-up a can of worms
related to locking dependencies in cpufreq.

Patch here defines the need for dbs_mutex and cleans up its usage in
ondemand governor. This also resolves the lockdep warnings reported here

http://lkml.indiana.edu/hypermail/linux/kernel/0906.1/01925.html
http://lkml.indiana.edu/hypermail/linux/kernel/0907.0/00820.html

and few others..

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
---
drivers/cpufreq/cpufreq.c | 4 ++--
drivers/cpufreq/cpufreq_conservative.c | 27 +++++++++++----------------
drivers/cpufreq/cpufreq_ondemand.c | 27 +++++++++++----------------
3 files changed, 24 insertions(+), 34 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 6e2ec0b..c7fe16e 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1070,8 +1070,6 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
#endif

- unlock_policy_rwsem_write(cpu);
-
if (cpufreq_driver->target)
__cpufreq_governor(data, CPUFREQ_GOV_STOP);

@@ -1088,6 +1086,8 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
if (cpufreq_driver->exit)
cpufreq_driver->exit(data);

+ unlock_policy_rwsem_write(cpu);
+
free_cpumask_var(data->related_cpus);
free_cpumask_var(data->cpus);
kfree(data);
diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index 7fc58af..58889f2 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -70,15 +70,10 @@ static DEFINE_PER_CPU(struct cpu_dbs_info_s, cpu_dbs_info);
static unsigned int dbs_enable; /* number of CPUs using this policy */

/*
- * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug
- * lock and dbs_mutex. cpu_hotplug lock should always be held before
- * dbs_mutex. If any function that can potentially take cpu_hotplug lock
- * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then
- * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock
- * is recursive for the same process. -Venki
- * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, because it
- * would deadlock with cancel_delayed_work_sync(), which is needed for proper
- * raceless workqueue teardown.
+ * dbs_mutex protects data in dbs_tuners_ins from concurrent changes on
+ * different CPUs. It protects dbs_enable in governor start/stop. It also
+ * serializes governor limit_change with do_dbs_timer. We do not want
+ * do_dbs_timer to run when user is changing the governor or limits.
*/
static DEFINE_MUTEX(dbs_mutex);

@@ -488,18 +483,17 @@ static void do_dbs_timer(struct work_struct *work)

delay -= jiffies % delay;

- if (lock_policy_rwsem_write(cpu) < 0)
- return;
+ mutex_lock(&dbs_mutex);

if (!dbs_info->enable) {
- unlock_policy_rwsem_write(cpu);
+ mutex_unlock(&dbs_mutex);
return;
}

dbs_check_cpu(dbs_info);

queue_delayed_work_on(cpu, kconservative_wq, &dbs_info->work, delay);
- unlock_policy_rwsem_write(cpu);
+ mutex_unlock(&dbs_mutex);
}

static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
@@ -590,15 +584,16 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
&dbs_cpufreq_notifier_block,
CPUFREQ_TRANSITION_NOTIFIER);
}
- dbs_timer_init(this_dbs_info);
-
mutex_unlock(&dbs_mutex);

+ dbs_timer_init(this_dbs_info);
+
break;

case CPUFREQ_GOV_STOP:
- mutex_lock(&dbs_mutex);
dbs_timer_exit(this_dbs_info);
+
+ mutex_lock(&dbs_mutex);
sysfs_remove_group(&policy->kobj, &dbs_attr_group);
dbs_enable--;

diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 1911d17..246ae14 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -78,15 +78,10 @@ static DEFINE_PER_CPU(struct cpu_dbs_info_s, cpu_dbs_info);
static unsigned int dbs_enable; /* number of CPUs using this policy */

/*
- * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug
- * lock and dbs_mutex. cpu_hotplug lock should always be held before
- * dbs_mutex. If any function that can potentially take cpu_hotplug lock
- * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then
- * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock
- * is recursive for the same process. -Venki
- * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, because it
- * would deadlock with cancel_delayed_work_sync(), which is needed for proper
- * raceless workqueue teardown.
+ * dbs_mutex protects data in dbs_tuners_ins from concurrent changes on
+ * different CPUs. It protects dbs_enable in governor start/stop. It also
+ * serializes governor limit_change with do_dbs_timer. We do not want
+ * do_dbs_timer to run when user is changing the governor or limits.
*/
static DEFINE_MUTEX(dbs_mutex);

@@ -494,11 +489,10 @@ static void do_dbs_timer(struct work_struct *work)

delay -= jiffies % delay;

- if (lock_policy_rwsem_write(cpu) < 0)
- return;
+ mutex_lock(&dbs_mutex);

if (!dbs_info->enable) {
- unlock_policy_rwsem_write(cpu);
+ mutex_unlock(&dbs_mutex);
return;
}

@@ -517,7 +511,7 @@ static void do_dbs_timer(struct work_struct *work)
dbs_info->freq_lo, CPUFREQ_RELATION_H);
}
queue_delayed_work_on(cpu, kondemand_wq, &dbs_info->work, delay);
- unlock_policy_rwsem_write(cpu);
+ mutex_unlock(&dbs_mutex);
}

static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
@@ -598,14 +592,15 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
max(min_sampling_rate,
latency * LATENCY_MULTIPLIER);
}
- dbs_timer_init(this_dbs_info);
-
mutex_unlock(&dbs_mutex);
+
+ dbs_timer_init(this_dbs_info);
break;

case CPUFREQ_GOV_STOP:
- mutex_lock(&dbs_mutex);
dbs_timer_exit(this_dbs_info);
+
+ mutex_lock(&dbs_mutex);
sysfs_remove_group(&policy->kobj, &dbs_attr_group);
dbs_enable--;
mutex_unlock(&dbs_mutex);
--
1.6.0.6
--



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