[PATCH 1/2] CPUFREQ: Remove unneeded dbs_mutexes from ondemand and conservative governors

[Thomas Renninger <trenn@suse.de>]

Comment from Venkatesh:
...
This mutex is just serializing the changes to those variables. I could't
think of any functionality issues of not having the lock as such.

-> rip it out.

CC: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Thomas Renninger <trenn@suse.de>
---
 drivers/cpufreq/cpufreq_conservative.c |   61 +++-----------------------------
 drivers/cpufreq/cpufreq_ondemand.c     |   48 +++----------------------
 2 files changed, 10 insertions(+), 99 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index 7a74d17..6303379 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -18,7 +18,6 @@
 #include <linux/cpu.h>
 #include <linux/jiffies.h>
 #include <linux/kernel_stat.h>
-#include <linux/mutex.h>
 #include <linux/hrtimer.h>
 #include <linux/tick.h>
 #include <linux/ktime.h>
@@ -84,19 +83,6 @@ 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.
- */
-static DEFINE_MUTEX(dbs_mutex);
-
 static struct workqueue_struct	*kconservative_wq;
 
 static struct dbs_tuners {
@@ -236,10 +222,7 @@ static ssize_t store_sampling_down_factor(struct cpufreq_policy *unused,
 	if (ret != 1 || input > MAX_SAMPLING_DOWN_FACTOR || input < 1)
 		return -EINVAL;
 
-	mutex_lock(&dbs_mutex);
 	dbs_tuners_ins.sampling_down_factor = input;
-	mutex_unlock(&dbs_mutex);
-
 	return count;
 }
 
@@ -253,10 +236,7 @@ static ssize_t store_sampling_rate(struct cpufreq_policy *unused,
 	if (ret != 1)
 		return -EINVAL;
 
-	mutex_lock(&dbs_mutex);
 	dbs_tuners_ins.sampling_rate = max(input, minimum_sampling_rate());
-	mutex_unlock(&dbs_mutex);
-
 	return count;
 }
 
@@ -267,16 +247,11 @@ static ssize_t store_up_threshold(struct cpufreq_policy *unused,
 	int ret;
 	ret = sscanf(buf, "%u", &input);
 
-	mutex_lock(&dbs_mutex);
 	if (ret != 1 || input > 100 ||
-			input <= dbs_tuners_ins.down_threshold) {
-		mutex_unlock(&dbs_mutex);
+			input <= dbs_tuners_ins.down_threshold)
 		return -EINVAL;
-	}
 
 	dbs_tuners_ins.up_threshold = input;
-	mutex_unlock(&dbs_mutex);
-
 	return count;
 }
 
@@ -287,17 +262,12 @@ static ssize_t store_down_threshold(struct cpufreq_policy *unused,
 	int ret;
 	ret = sscanf(buf, "%u", &input);
 
-	mutex_lock(&dbs_mutex);
 	/* cannot be lower than 11 otherwise freq will not fall */
 	if (ret != 1 || input < 11 || input > 100 ||
-			input >= dbs_tuners_ins.up_threshold) {
-		mutex_unlock(&dbs_mutex);
+			input >= dbs_tuners_ins.up_threshold)
 		return -EINVAL;
-	}
 
 	dbs_tuners_ins.down_threshold = input;
-	mutex_unlock(&dbs_mutex);
-
 	return count;
 }
 
@@ -316,11 +286,9 @@ static ssize_t store_ignore_nice_load(struct cpufreq_policy *policy,
 	if (input > 1)
 		input = 1;
 
-	mutex_lock(&dbs_mutex);
-	if (input == dbs_tuners_ins.ignore_nice) { /* nothing to do */
-		mutex_unlock(&dbs_mutex);
+	if (input == dbs_tuners_ins.ignore_nice) /* nothing to do */
 		return count;
-	}
+
 	dbs_tuners_ins.ignore_nice = input;
 
 	/* we need to re-evaluate prev_cpu_idle */
@@ -332,8 +300,6 @@ static ssize_t store_ignore_nice_load(struct cpufreq_policy *policy,
 		if (dbs_tuners_ins.ignore_nice)
 			dbs_info->prev_cpu_nice = kstat_cpu(j).cpustat.nice;
 	}
-	mutex_unlock(&dbs_mutex);
-
 	return count;
 }
 
@@ -352,10 +318,7 @@ static ssize_t store_freq_step(struct cpufreq_policy *policy,
 
 	/* no need to test here if freq_step is zero as the user might actually
 	 * want this, they would be crazy though :) */
-	mutex_lock(&dbs_mutex);
 	dbs_tuners_ins.freq_step = input;
-	mutex_unlock(&dbs_mutex);
-
 	return count;
 }
 
@@ -566,13 +529,9 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 		if (this_dbs_info->enable) /* Already enabled */
 			break;
 
-		mutex_lock(&dbs_mutex);
-
 		rc = sysfs_create_group(&policy->kobj, &dbs_attr_group);
-		if (rc) {
-			mutex_unlock(&dbs_mutex);
+		if (rc)
 			return rc;
-		}
 
 		for_each_cpu(j, policy->cpus) {
 			struct cpu_dbs_info_s *j_dbs_info;
@@ -612,13 +571,9 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 					CPUFREQ_TRANSITION_NOTIFIER);
 		}
 		dbs_timer_init(this_dbs_info);
-
-		mutex_unlock(&dbs_mutex);
-
 		break;
 
 	case CPUFREQ_GOV_STOP:
-		mutex_lock(&dbs_mutex);
 		dbs_timer_exit(this_dbs_info);
 		sysfs_remove_group(&policy->kobj, &dbs_attr_group);
 		dbs_enable--;
@@ -631,13 +586,9 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 			cpufreq_unregister_notifier(
 					&dbs_cpufreq_notifier_block,
 					CPUFREQ_TRANSITION_NOTIFIER);
-
-		mutex_unlock(&dbs_mutex);
-
 		break;
 
 	case CPUFREQ_GOV_LIMITS:
-		mutex_lock(&dbs_mutex);
 		if (policy->max < this_dbs_info->cur_policy->cur)
 			__cpufreq_driver_target(
 					this_dbs_info->cur_policy,
@@ -646,8 +597,6 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 			__cpufreq_driver_target(
 					this_dbs_info->cur_policy,
 					policy->min, CPUFREQ_RELATION_L);
-		mutex_unlock(&dbs_mutex);
-
 		break;
 	}
 	return 0;
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index e741c33..d080a48 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -17,7 +17,6 @@
 #include <linux/cpu.h>
 #include <linux/jiffies.h>
 #include <linux/kernel_stat.h>
-#include <linux/mutex.h>
 #include <linux/hrtimer.h>
 #include <linux/tick.h>
 #include <linux/ktime.h>
@@ -91,19 +90,6 @@ 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.
- */
-static DEFINE_MUTEX(dbs_mutex);
-
 static struct workqueue_struct	*kondemand_wq;
 
 static struct dbs_tuners {
@@ -269,14 +255,10 @@ static ssize_t store_sampling_rate(struct cpufreq_policy *unused,
 	int ret;
 	ret = sscanf(buf, "%u", &input);
 
-	mutex_lock(&dbs_mutex);
-	if (ret != 1) {
-		mutex_unlock(&dbs_mutex);
+	if (ret != 1)
 		return -EINVAL;
-	}
-	dbs_tuners_ins.sampling_rate = max(input, minimum_sampling_rate());
-	mutex_unlock(&dbs_mutex);
 
+	dbs_tuners_ins.sampling_rate = max(input, minimum_sampling_rate());
 	return count;
 }
 
@@ -287,16 +269,11 @@ static ssize_t store_up_threshold(struct cpufreq_policy *unused,
 	int ret;
 	ret = sscanf(buf, "%u", &input);
 
-	mutex_lock(&dbs_mutex);
 	if (ret != 1 || input > MAX_FREQUENCY_UP_THRESHOLD ||
-			input < MIN_FREQUENCY_UP_THRESHOLD) {
-		mutex_unlock(&dbs_mutex);
+			input < MIN_FREQUENCY_UP_THRESHOLD)
 		return -EINVAL;
-	}
 
 	dbs_tuners_ins.up_threshold = input;
-	mutex_unlock(&dbs_mutex);
-
 	return count;
 }
 
@@ -315,11 +292,9 @@ static ssize_t store_ignore_nice_load(struct cpufreq_policy *policy,
 	if (input > 1)
 		input = 1;
 
-	mutex_lock(&dbs_mutex);
-	if (input == dbs_tuners_ins.ignore_nice) { /* nothing to do */
-		mutex_unlock(&dbs_mutex);
+	if (input == dbs_tuners_ins.ignore_nice) /* nothing to do */
 		return count;
-	}
+
 	dbs_tuners_ins.ignore_nice = input;
 
 	/* we need to re-evaluate prev_cpu_idle */
@@ -332,8 +307,6 @@ static ssize_t store_ignore_nice_load(struct cpufreq_policy *policy,
 			dbs_info->prev_cpu_nice = kstat_cpu(j).cpustat.nice;
 
 	}
-	mutex_unlock(&dbs_mutex);
-
 	return count;
 }
 
@@ -350,10 +323,8 @@ static ssize_t store_powersave_bias(struct cpufreq_policy *unused,
 	if (input > 1000)
 		input = 1000;
 
-	mutex_lock(&dbs_mutex);
 	dbs_tuners_ins.powersave_bias = input;
 	ondemand_powersave_bias_init();
-	mutex_unlock(&dbs_mutex);
 
 	return count;
 }
@@ -586,13 +557,11 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 		if (this_dbs_info->enable) /* Already enabled */
 			break;
 
-		mutex_lock(&dbs_mutex);
 		dbs_enable++;
 
 		rc = sysfs_create_group(&policy->kobj, &dbs_attr_group);
 		if (rc) {
 			dbs_enable--;
-			mutex_unlock(&dbs_mutex);
 			return rc;
 		}
 
@@ -627,28 +596,21 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 			dbs_tuners_ins.sampling_rate = def_sampling_rate;
 		}
 		dbs_timer_init(this_dbs_info);
-
-		mutex_unlock(&dbs_mutex);
 		break;
 
 	case CPUFREQ_GOV_STOP:
-		mutex_lock(&dbs_mutex);
 		dbs_timer_exit(this_dbs_info);
 		sysfs_remove_group(&policy->kobj, &dbs_attr_group);
 		dbs_enable--;
-		mutex_unlock(&dbs_mutex);
-
 		break;
 
 	case CPUFREQ_GOV_LIMITS:
-		mutex_lock(&dbs_mutex);
 		if (policy->max < this_dbs_info->cur_policy->cur)
 			__cpufreq_driver_target(this_dbs_info->cur_policy,
 				policy->max, CPUFREQ_RELATION_H);
 		else if (policy->min > this_dbs_info->cur_policy->cur)
 			__cpufreq_driver_target(this_dbs_info->cur_policy,
 				policy->min, CPUFREQ_RELATION_L);
-		mutex_unlock(&dbs_mutex);
 		break;
 	}
 	return 0;
-- 
1.6.0.2