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Subject[PATCH] cpufreq: remove dbs_mutex

* Thomas Renninger <trenn@suse.de> wrote:

> > Note, this bug warning still triggers rather frequently with
> > latest -git (fb20871) during bootup on two test-systems -
> > relevant portion of the bootlog attached below. As usual i can
> > test any fix for this.
>
> Best rip out the dbs_mutex in drivers/cpufreq/cpufreq_ondemand.c
> totally. I can provide several locking cleanups for cpufreq for
> .31 the next days, including dbs_mutex removal, which I think is
> not needed. The dbs_mutex removal which should fix this could then
> be marked: CC: stable@kernel.org

drivers/cpufreq/cpufreq_conservative.c too i guess?

Something like the patch below?

Utterly untested and such.

Ingo

---------------->
From 750e2309db0287a979f4295aeaef68d39bacd124 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Tue, 23 Jun 2009 20:12:48 +0200
Subject: [PATCH] cpufreq: remove dbs_mutex

As per the cpufreq people's recommendation, remove all uses of
dbs_mutex.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
drivers/cpufreq/cpufreq_conservative.c | 40 --------------------------------
drivers/cpufreq/cpufreq_ondemand.c | 31 ------------------------
2 files changed, 0 insertions(+), 71 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index 7fc58af..3c427f5 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -69,19 +69,6 @@ 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 {
@@ -208,9 +195,7 @@ 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;
}
@@ -225,9 +210,7 @@ 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, min_sampling_rate);
- mutex_unlock(&dbs_mutex);

return count;
}
@@ -239,15 +222,12 @@ 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);
return -EINVAL;
}

dbs_tuners_ins.up_threshold = input;
- mutex_unlock(&dbs_mutex);

return count;
}
@@ -259,16 +239,13 @@ 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);
return -EINVAL;
}

dbs_tuners_ins.down_threshold = input;
- mutex_unlock(&dbs_mutex);

return count;
}
@@ -288,9 +265,7 @@ 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);
return count;
}
dbs_tuners_ins.ignore_nice = input;
@@ -304,7 +279,6 @@ 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;
}
@@ -324,9 +298,7 @@ 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;
}
@@ -538,11 +510,8 @@ 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);
return rc;
}

@@ -592,12 +561,9 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
}
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--;
@@ -610,13 +576,9 @@ 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,
@@ -625,8 +587,6 @@ 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 1911d17..054c10b 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -77,19 +77,6 @@ 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 {
@@ -241,13 +228,10 @@ 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);
return -EINVAL;
}
dbs_tuners_ins.sampling_rate = max(input, min_sampling_rate);
- mutex_unlock(&dbs_mutex);

return count;
}
@@ -259,15 +243,12 @@ 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);
return -EINVAL;
}

dbs_tuners_ins.up_threshold = input;
- mutex_unlock(&dbs_mutex);

return count;
}
@@ -287,9 +268,7 @@ 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);
return count;
}
dbs_tuners_ins.ignore_nice = input;
@@ -304,7 +283,6 @@ 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;
}
@@ -322,10 +300,8 @@ 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;
}
@@ -558,13 +534,11 @@ 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;
}

@@ -600,27 +574,22 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
}
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;

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