[v5] cpufreq: split the cpufreq_driver_lock and use the rcu (was cpufreq: cpufreq_driver_lock is hot on large systems)

Commit Message

Nathan Zimmer April 1, 2013, 3:33 p.m. UTC

The cpufreq_driver_lock is hot with some configs.
This lock covers both cpufreq_driver and cpufreq_cpu_data so part one of the
proposed fix is to split up the lock abit.
cpufreq_cpu_data is now covered by the cpufreq_data_lock.
cpufreq_driver is now covered by the cpufreq_driver lock and the rcu.

This means that the cpufreq_driver_lock is no longer hot.
There remains some measurable heat on the cpufreq_data_lock it is significantly 
less then previous measured though. 

Cc: Viresh Kumar <[e-mail]>
Cc: "Rafael J. Wysocki" <[e-mail]>
Signed-off-by: Nathan Zimmer <[e-mail]>
---
 drivers/cpufreq/cpufreq.c | 305 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 222 insertions(+), 83 deletions(-)

Comments

Viresh Kumar April 1, 2013, 4:28 p.m. UTC | #1

Hi Nathan,

Welcome back :)

On 1 April 2013 21:03, Nathan Zimmer <[e-mail]> wrote:

You need to resent this patch as we don't want current mail subject as commit
subject.. You could have used the area after three dashes "-" inside the
commit for logs which you don't want to commit.

> The cpufreq_driver_lock is hot with some configs.
> This lock covers both cpufreq_driver and cpufreq_cpu_data so part one of the

s/ so/, so/

> proposed fix is to split up the lock abit.

s/abit/a bit/

What's the other part?

> cpufreq_cpu_data is now covered by the cpufreq_data_lock.
> cpufreq_driver is now covered by the cpufreq_driver lock and the rcu.
>
> This means that the cpufreq_driver_lock is no longer hot.
> There remains some measurable heat on the cpufreq_data_lock it is significantly

s/it/but it/

> less then previous measured though.
>
> Cc: Viresh Kumar <[e-mail]>
> Cc: "Rafael J. Wysocki" <[e-mail]>
> Signed-off-by: Nathan Zimmer <[e-mail]>
> ---
>  drivers/cpufreq/cpufreq.c | 305 +++++++++++++++++++++++++++++++++-------------
>  1 file changed, 222 insertions(+), 83 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c

> @@ -329,11 +339,23 @@ static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
>                                 struct cpufreq_governor **governor)
>  {
>         int err = -EINVAL;
> -
> -       if (!cpufreq_driver)
> +       struct cpufreq_driver *driver;
> +       int (*setpolicy)(struct cpufreq_policy *policy);
> +       int (*target)(struct cpufreq_policy *policy,
> +                     unsigned int target_freq,
> +                     unsigned int relation);

You can keep bools here instead of complex function pointers.
setpolicy_supported and target_supported

> +       rcu_read_lock();
> +       driver = rcu_dereference(cpufreq_driver);
> +       if (!driver) {
> +               rcu_read_unlock();
>                 goto out;
> +       }
> +       setpolicy = driver->setpolicy;
> +       target = driver->target;
> +       rcu_read_unlock();
>
> -       if (cpufreq_driver->setpolicy) {
> +       if (setpolicy) {
>                 if (!strnicmp(str_governor, "performance", CPUFREQ_NAME_LEN)) {
>                         *policy = CPUFREQ_POLICY_PERFORMANCE;
>                         err = 0;
> @@ -342,7 +364,7 @@ static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
>                         *policy = CPUFREQ_POLICY_POWERSAVE;
>                         err = 0;
>                 }
> -       } else if (cpufreq_driver->target) {
> +       } else if (target) {
>                 struct cpufreq_governor *t;
>
>                 mutex_lock(&cpufreq_governor_mutex);

> @@ -731,6 +766,8 @@ static int cpufreq_add_dev_interface(unsigned int cpu,
>  {
>         struct cpufreq_policy new_policy;
>         struct freq_attr **drv_attr;
> +       struct cpufreq_driver *driver;
> +       int (*exit)(struct cpufreq_policy *policy);

Declare it in the block which used it.

>         if (ret) {
>                 pr_debug("setting policy failed\n");
> -               if (cpufreq_driver->exit)
> -                       cpufreq_driver->exit(policy);
> +               rcu_read_lock();
> +               exit = rcu_dereference(cpufreq_driver)->exit;
> +               if (exit)
> +                       exit(policy);
> +               rcu_read_unlock();
> +
>         }

> @@ -1002,32 +1059,42 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
>         unsigned int cpu = dev->id, ret, cpus;
>         unsigned long flags;
>         struct cpufreq_policy *data;
> +       struct cpufreq_driver *driver;
>         struct kobject *kobj;
>         struct completion *cmp;
>         struct device *cpu_dev;
> +       int (*target)(struct cpufreq_policy *policy,
> +                      unsigned int target_freq,
> +                      unsigned int relation);

can be bool?

> +       int (*exit)(struct cpufreq_policy *policy);
>


One more generic comment: What about a reader-writer lock for
cpufreq_data_lock??
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Nathan Zimmer April 1, 2013, 5:17 p.m. UTC | #2

On 04/01/2013 11:28 AM, Viresh Kumar wrote:
> Hi Nathan,
>
> Welcome back :)
>
> On 1 April 2013 21:03, Nathan Zimmer <[e-mail]> wrote:
>
> You need to resent this patch as we don't want current mail subject as commit
> subject.. You could have used the area after three dashes "-" inside the
> commit for logs which you don't want to commit.
Ok.
>> The cpufreq_driver_lock is hot with some configs.
>> This lock covers both cpufreq_driver and cpufreq_cpu_data so part one of the
> s/ so/, so/
>
>> proposed fix is to split up the lock abit.
> s/abit/a bit/
>
> What's the other part?
>
>> cpufreq_cpu_data is now covered by the cpufreq_data_lock.
>> cpufreq_driver is now covered by the cpufreq_driver lock and the rcu.
>>
>> This means that the cpufreq_driver_lock is no longer hot.
>> There remains some measurable heat on the cpufreq_data_lock it is significantly
> s/it/but it/

>> less then previous measured though.
>>
>> Cc: Viresh Kumar <[e-mail]>
>> Cc: "Rafael J. Wysocki" <[e-mail]>
>> Signed-off-by: Nathan Zimmer <[e-mail]>
>> ---
>>   drivers/cpufreq/cpufreq.c | 305 +++++++++++++++++++++++++++++++++-------------
>>   1 file changed, 222 insertions(+), 83 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> @@ -329,11 +339,23 @@ static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
>>                                  struct cpufreq_governor **governor)
>>   {
>>          int err = -EINVAL;
>> -
>> -       if (!cpufreq_driver)
>> +       struct cpufreq_driver *driver;
>> +       int (*setpolicy)(struct cpufreq_policy *policy);
>> +       int (*target)(struct cpufreq_policy *policy,
>> +                     unsigned int target_freq,
>> +                     unsigned int relation);
> You can keep bools here instead of complex function pointers.
> setpolicy_supported and target_supported
Good point.  In a few places I needed the function pointer but not here.
I'll convert the unneeded ones to bools and resend.

>> +       rcu_read_lock();
>> +       driver = rcu_dereference(cpufreq_driver);
>> +       if (!driver) {
>> +               rcu_read_unlock();
>>                  goto out;
>> +       }
>> +       setpolicy = driver->setpolicy;
>> +       target = driver->target;
>> +       rcu_read_unlock();
>>
>> -       if (cpufreq_driver->setpolicy) {
>> +       if (setpolicy) {
>>                  if (!strnicmp(str_governor, "performance", CPUFREQ_NAME_LEN)) {
>>                          *policy = CPUFREQ_POLICY_PERFORMANCE;
>>                          err = 0;
>> @@ -342,7 +364,7 @@ static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
>>                          *policy = CPUFREQ_POLICY_POWERSAVE;
>>                          err = 0;
>>                  }
>> -       } else if (cpufreq_driver->target) {
>> +       } else if (target) {
>>                  struct cpufreq_governor *t;
>>
>>                  mutex_lock(&cpufreq_governor_mutex);
>> @@ -731,6 +766,8 @@ static int cpufreq_add_dev_interface(unsigned int cpu,
>>   {
>>          struct cpufreq_policy new_policy;
>>          struct freq_attr **drv_attr;
>> +       struct cpufreq_driver *driver;
>> +       int (*exit)(struct cpufreq_policy *policy);
> Declare it in the block which used it.
>
>>          if (ret) {
>>                  pr_debug("setting policy failed\n");
>> -               if (cpufreq_driver->exit)
>> -                       cpufreq_driver->exit(policy);
>> +               rcu_read_lock();
>> +               exit = rcu_dereference(cpufreq_driver)->exit;
>> +               if (exit)
>> +                       exit(policy);
>> +               rcu_read_unlock();
>> +
>>          }
>> @@ -1002,32 +1059,42 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
>>          unsigned int cpu = dev->id, ret, cpus;
>>          unsigned long flags;
>>          struct cpufreq_policy *data;
>> +       struct cpufreq_driver *driver;
>>          struct kobject *kobj;
>>          struct completion *cmp;That
>>          struct device *cpu_dev;
>> +       int (*target)(struct cpufreq_policy *policy,
>> +                      unsigned int target_freq,
>> +                      unsigned int relation);
> can be bool?
>
>> +       int (*exit)(struct cpufreq_policy *policy);
>>
>
> One more generic comment: What about a reader-writer lock for
> cpufreq_data_lock??
I had been looking for ways to use the rcu but wasn't having much success.
Let me try a rwlock and grab some numbers after lunch.
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Nathan Zimmer April 1, 2013, 8:11 p.m. UTC | #3

I am noticing the cpufreq_driver_lock is quite hot.
On an idle 512 system perf shows me most of the system time is spent on this
lock.  This is quite significant as top shows 5% of time in system time.
My solution was to first split the lock into two parts, cpu_driver_lock and 
cpu_data_lock, with the cpufreq_driver also being protected by the RCU.
There was measurable heat left on the cpufreq_data_lock in __cpufreq_cpu_get.
So in the second part I converted the cpufreq_data_lock to be a rw lock since
an rcu solution was not apparent, at least to me.

v5: Go a different way and split up the lock and use the rcu
v6: use bools instead of checking function pointers
    covert the cpufreq_data_lock to a rwlock

Nathan Zimmer (2):
  cpufreq: split the cpufreq_driver_lock and use the rcu
  cpufreq: covert the cpufreq_data_lock to a spinlock

 drivers/cpufreq/cpufreq.c | 302 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 219 insertions(+), 83 deletions(-)

Patch

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index b02824d..387a5f8 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -39,13 +39,15 @@ 
  * level driver of CPUFreq support, and its spinlock. This lock
  * also protects the cpufreq_cpu_data array.
  */
-static struct cpufreq_driver *cpufreq_driver;
+static struct cpufreq_driver __rcu *cpufreq_driver;
+static DEFINE_SPINLOCK(cpufreq_driver_lock);
+
+static DEFINE_SPINLOCK(cpufreq_data_lock);
 static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
 #ifdef CONFIG_HOTPLUG_CPU
 /* This one keeps track of the previously set governor of a removed CPU */
 static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
 #endif
-static DEFINE_SPINLOCK(cpufreq_driver_lock);
 
 /*
  * cpu_policy_rwsem is a per CPU reader-writer semaphore designed to cure
@@ -131,22 +133,24 @@  static DEFINE_MUTEX(cpufreq_governor_mutex);
 static struct cpufreq_policy *__cpufreq_cpu_get(unsigned int cpu, bool sysfs)
 {
 	struct cpufreq_policy *data;
+	struct cpufreq_driver *driver;
 	unsigned long flags;
 
 	if (cpu >= nr_cpu_ids)
 		goto err_out;
 
 	/* get the cpufreq driver */
-	spin_lock_irqsave(&cpufreq_driver_lock, flags);
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
 
-	if (!cpufreq_driver)
+	if (!driver)
 		goto err_out_unlock;
 
-	if (!try_module_get(cpufreq_driver->owner))
+	if (!try_module_get(driver->owner))
 		goto err_out_unlock;
 
-
 	/* get the CPU */
+	spin_lock_irqsave(&cpufreq_data_lock, flags);
 	data = per_cpu(cpufreq_cpu_data, cpu);
 
 	if (!data)
@@ -155,13 +159,15 @@  static struct cpufreq_policy *__cpufreq_cpu_get(unsigned int cpu, bool sysfs)
 	if (!sysfs && !kobject_get(&data->kobj))
 		goto err_out_put_module;
 
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	spin_unlock_irqrestore(&cpufreq_data_lock, flags);
+	rcu_read_unlock();
 	return data;
 
 err_out_put_module:
-	module_put(cpufreq_driver->owner);
+	module_put(driver->owner);
+	spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 err_out_unlock:
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	rcu_read_unlock();
 err_out:
 	return NULL;
 }
@@ -184,7 +190,9 @@  static void __cpufreq_cpu_put(struct cpufreq_policy *data, bool sysfs)
 {
 	if (!sysfs)
 		kobject_put(&data->kobj);
-	module_put(cpufreq_driver->owner);
+	rcu_read_lock();
+	module_put(rcu_dereference(cpufreq_driver)->owner);
+	rcu_read_unlock();
 }
 
 void cpufreq_cpu_put(struct cpufreq_policy *data)
@@ -262,13 +270,15 @@  void cpufreq_notify_transition(struct cpufreq_freqs *freqs, unsigned int state)
 	if (cpufreq_disabled())
 		return;
 
-	freqs->flags = cpufreq_driver->flags;
+	rcu_read_lock();
+	freqs->flags = rcu_dereference(cpufreq_driver)->flags;
+	rcu_read_unlock();
 	pr_debug("notification %u of frequency transition to %u kHz\n",
 		state, freqs->new);
 
-	spin_lock_irqsave(&cpufreq_driver_lock, flags);
+	spin_lock_irqsave(&cpufreq_data_lock, flags);
 	policy = per_cpu(cpufreq_cpu_data, freqs->cpu);
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 
 	switch (state) {
 
@@ -277,7 +287,7 @@  void cpufreq_notify_transition(struct cpufreq_freqs *freqs, unsigned int state)
 		 * which is not equal to what the cpufreq core thinks is
 		 * "old frequency".
 		 */
-		if (!(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
+		if (!(freqs->flags & CPUFREQ_CONST_LOOPS)) {
 			if ((policy) && (policy->cpu == freqs->cpu) &&
 			    (policy->cur) && (policy->cur != freqs->old)) {
 				pr_debug("Warning: CPU frequency is"
@@ -329,11 +339,23 @@  static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
 				struct cpufreq_governor **governor)
 {
 	int err = -EINVAL;
-
-	if (!cpufreq_driver)
+	struct cpufreq_driver *driver;
+	int (*setpolicy)(struct cpufreq_policy *policy);
+	int (*target)(struct cpufreq_policy *policy,
+		      unsigned int target_freq,
+		      unsigned int relation);
+
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
+	if (!driver) {
+		rcu_read_unlock();
 		goto out;
+	}
+	setpolicy = driver->setpolicy;
+	target = driver->target;
+	rcu_read_unlock();
 
-	if (cpufreq_driver->setpolicy) {
+	if (setpolicy) {
 		if (!strnicmp(str_governor, "performance", CPUFREQ_NAME_LEN)) {
 			*policy = CPUFREQ_POLICY_PERFORMANCE;
 			err = 0;
@@ -342,7 +364,7 @@  static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
 			*policy = CPUFREQ_POLICY_POWERSAVE;
 			err = 0;
 		}
-	} else if (cpufreq_driver->target) {
+	} else if (target) {
 		struct cpufreq_governor *t;
 
 		mutex_lock(&cpufreq_governor_mutex);
@@ -493,7 +515,11 @@  static ssize_t store_scaling_governor(struct cpufreq_policy *policy,
  */
 static ssize_t show_scaling_driver(struct cpufreq_policy *policy, char *buf)
 {
-	return scnprintf(buf, CPUFREQ_NAME_PLEN, "%s\n", cpufreq_driver->name);
+	char *name;
+	rcu_read_lock();
+	name = rcu_dereference(cpufreq_driver)->name;
+	rcu_read_unlock();
+	return scnprintf(buf, CPUFREQ_NAME_PLEN, "%s\n", name);
 }
 
 /**
@@ -505,10 +531,13 @@  static ssize_t show_scaling_available_governors(struct cpufreq_policy *policy,
 	ssize_t i = 0;
 	struct cpufreq_governor *t;
 
-	if (!cpufreq_driver->target) {
+	rcu_read_lock();
+	if (!rcu_dereference(cpufreq_driver)->target) {
 		i += sprintf(buf, "performance powersave");
+		rcu_read_unlock();
 		goto out;
 	}
+	rcu_read_unlock();
 
 	list_for_each_entry(t, &cpufreq_governor_list, governor_list) {
 		if (i >= (ssize_t) ((PAGE_SIZE / sizeof(char))
@@ -586,9 +615,15 @@  static ssize_t show_scaling_setspeed(struct cpufreq_policy *policy, char *buf)
 static ssize_t show_bios_limit(struct cpufreq_policy *policy, char *buf)
 {
 	unsigned int limit;
+	int (*bios_limit)(int cpu, unsigned int *limit);
 	int ret;
-	if (cpufreq_driver->bios_limit) {
-		ret = cpufreq_driver->bios_limit(policy->cpu, &limit);
+
+	rcu_read_lock();
+	bios_limit = rcu_dereference(cpufreq_driver)->bios_limit;
+	rcu_read_unlock();
+
+	if (bios_limit) {
+		ret = bios_limit(policy->cpu, &limit);
 		if (!ret)
 			return sprintf(buf, "%u\n", limit);
 	}
@@ -731,6 +766,8 @@  static int cpufreq_add_dev_interface(unsigned int cpu,
 {
 	struct cpufreq_policy new_policy;
 	struct freq_attr **drv_attr;
+	struct cpufreq_driver *driver;
+	int (*exit)(struct cpufreq_policy *policy);
 	unsigned long flags;
 	int ret = 0;
 	unsigned int j;
@@ -742,35 +779,38 @@  static int cpufreq_add_dev_interface(unsigned int cpu,
 		return ret;
 
 	/* set up files for this cpu device */
-	drv_attr = cpufreq_driver->attr;
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
+	drv_attr = driver->attr;
 	while ((drv_attr) && (*drv_attr)) {
 		ret = sysfs_create_file(&policy->kobj, &((*drv_attr)->attr));
 		if (ret)
-			goto err_out_kobj_put;
+			goto err_out_unlock;
 		drv_attr++;
 	}
-	if (cpufreq_driver->get) {
+	if (driver->get) {
 		ret = sysfs_create_file(&policy->kobj, &cpuinfo_cur_freq.attr);
 		if (ret)
-			goto err_out_kobj_put;
+			goto err_out_unlock;
 	}
-	if (cpufreq_driver->target) {
+	if (driver->target) {
 		ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
 		if (ret)
-			goto err_out_kobj_put;
+			goto err_out_unlock;
 	}
-	if (cpufreq_driver->bios_limit) {
+	if (driver->bios_limit) {
 		ret = sysfs_create_file(&policy->kobj, &bios_limit.attr);
 		if (ret)
-			goto err_out_kobj_put;
+			goto err_out_unlock;
 	}
+	rcu_read_unlock();
 
-	spin_lock_irqsave(&cpufreq_driver_lock, flags);
+	spin_lock_irqsave(&cpufreq_data_lock, flags);
 	for_each_cpu(j, policy->cpus) {
 		per_cpu(cpufreq_cpu_data, j) = policy;
 		per_cpu(cpufreq_policy_cpu, j) = policy->cpu;
 	}
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 
 	ret = cpufreq_add_dev_symlink(cpu, policy);
 	if (ret)
@@ -787,11 +827,17 @@  static int cpufreq_add_dev_interface(unsigned int cpu,
 
 	if (ret) {
 		pr_debug("setting policy failed\n");
-		if (cpufreq_driver->exit)
-			cpufreq_driver->exit(policy);
+		rcu_read_lock();
+		exit = rcu_dereference(cpufreq_driver)->exit;
+		if (exit)
+			exit(policy);
+		rcu_read_unlock();
+
 	}
 	return ret;
 
+err_out_unlock:
+	rcu_read_unlock();
 err_out_kobj_put:
 	kobject_put(&policy->kobj);
 	wait_for_completion(&policy->kobj_unregister);
@@ -813,12 +859,12 @@  static int cpufreq_add_policy_cpu(unsigned int cpu, unsigned int sibling,
 
 	lock_policy_rwsem_write(sibling);
 
-	spin_lock_irqsave(&cpufreq_driver_lock, flags);
+	spin_lock_irqsave(&cpufreq_data_lock, flags);
 
 	cpumask_set_cpu(cpu, policy->cpus);
 	per_cpu(cpufreq_policy_cpu, cpu) = policy->cpu;
 	per_cpu(cpufreq_cpu_data, cpu) = policy;
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 
 	unlock_policy_rwsem_write(sibling);
 
@@ -849,6 +895,8 @@  static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
 	unsigned int j, cpu = dev->id;
 	int ret = -ENOMEM;
 	struct cpufreq_policy *policy;
+	struct cpufreq_driver *driver;
+	int (*init)(struct cpufreq_policy *policy);
 	unsigned long flags;
 #ifdef CONFIG_HOTPLUG_CPU
 	struct cpufreq_governor *gov;
@@ -871,22 +919,27 @@  static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
 
 #ifdef CONFIG_HOTPLUG_CPU
 	/* Check if this cpu was hot-unplugged earlier and has siblings */
-	spin_lock_irqsave(&cpufreq_driver_lock, flags);
+	spin_lock_irqsave(&cpufreq_data_lock, flags);
 	for_each_online_cpu(sibling) {
 		struct cpufreq_policy *cp = per_cpu(cpufreq_cpu_data, sibling);
 		if (cp && cpumask_test_cpu(cpu, cp->related_cpus)) {
-			spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+			spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 			return cpufreq_add_policy_cpu(cpu, sibling, dev);
 		}
 	}
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 #endif
 #endif
 
-	if (!try_module_get(cpufreq_driver->owner)) {
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
+	if (!try_module_get(driver->owner)) {
+		rcu_read_unlock();
 		ret = -EINVAL;
 		goto module_out;
 	}
+	init = driver->init;
+	rcu_read_unlock();
 
 	policy = kzalloc(sizeof(struct cpufreq_policy), GFP_KERNEL);
 	if (!policy)
@@ -911,7 +964,7 @@  static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
 	/* call driver. From then on the cpufreq must be able
 	 * to accept all calls to ->verify and ->setpolicy for this CPU
 	 */
-	ret = cpufreq_driver->init(policy);
+	ret = init(policy);
 	if (ret) {
 		pr_debug("initialization failed\n");
 		goto err_set_policy_cpu;
@@ -946,16 +999,18 @@  static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
 		goto err_out_unregister;
 
 	kobject_uevent(&policy->kobj, KOBJ_ADD);
-	module_put(cpufreq_driver->owner);
+	rcu_read_lock();
+	module_put(rcu_dereference(cpufreq_driver)->owner);
+	rcu_read_unlock();
 	pr_debug("initialization complete\n");
 
 	return 0;
 
 err_out_unregister:
-	spin_lock_irqsave(&cpufreq_driver_lock, flags);
+	spin_lock_irqsave(&cpufreq_data_lock, flags);
 	for_each_cpu(j, policy->cpus)
 		per_cpu(cpufreq_cpu_data, j) = NULL;
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 
 	kobject_put(&policy->kobj);
 	wait_for_completion(&policy->kobj_unregister);
@@ -968,7 +1023,9 @@  err_free_cpumask:
 err_free_policy:
 	kfree(policy);
 nomem_out:
-	module_put(cpufreq_driver->owner);
+	rcu_read_lock();
+	module_put(rcu_dereference(cpufreq_driver)->owner);
+	rcu_read_unlock();
 module_out:
 	return ret;
 }
@@ -1002,32 +1059,42 @@  static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
 	unsigned int cpu = dev->id, ret, cpus;
 	unsigned long flags;
 	struct cpufreq_policy *data;
+	struct cpufreq_driver *driver;
 	struct kobject *kobj;
 	struct completion *cmp;
 	struct device *cpu_dev;
+	int (*target)(struct cpufreq_policy *policy,
+		       unsigned int target_freq,
+		       unsigned int relation);
+	int (*exit)(struct cpufreq_policy *policy);
 
 	pr_debug("%s: unregistering CPU %u\n", __func__, cpu);
 
-	spin_lock_irqsave(&cpufreq_driver_lock, flags);
+	spin_lock_irqsave(&cpufreq_data_lock, flags);
 
 	data = per_cpu(cpufreq_cpu_data, cpu);
 	per_cpu(cpufreq_cpu_data, cpu) = NULL;
 
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 
 	if (!data) {
 		pr_debug("%s: No cpu_data found\n", __func__);
 		return -EINVAL;
 	}
 
-	if (cpufreq_driver->target)
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
+	target = driver->target;
+	exit = driver->exit;
+	if (target)
 		__cpufreq_governor(data, CPUFREQ_GOV_STOP);
 
 #ifdef CONFIG_HOTPLUG_CPU
-	if (!cpufreq_driver->setpolicy)
+	if (!driver->setpolicy)
 		strncpy(per_cpu(cpufreq_cpu_governor, cpu),
 			data->governor->name, CPUFREQ_NAME_LEN);
 #endif
+	rcu_read_unlock();
 
 	WARN_ON(lock_policy_rwsem_write(cpu));
 	cpus = cpumask_weight(data->cpus);
@@ -1047,9 +1114,9 @@  static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
 			WARN_ON(lock_policy_rwsem_write(cpu));
 			cpumask_set_cpu(cpu, data->cpus);
 
-			spin_lock_irqsave(&cpufreq_driver_lock, flags);
+			spin_lock_irqsave(&cpufreq_data_lock, flags);
 			per_cpu(cpufreq_cpu_data, cpu) = data;
-			spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+			spin_unlock_irqrestore(&cpufreq_data_lock, flags);
 
 			unlock_policy_rwsem_write(cpu);
 
@@ -1084,13 +1151,13 @@  static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
 		wait_for_completion(cmp);
 		pr_debug("wait complete\n");
 
-		if (cpufreq_driver->exit)
-			cpufreq_driver->exit(data);
+		if (exit)
+			exit(data);
 
 		free_cpumask_var(data->related_cpus);
 		free_cpumask_var(data->cpus);
 		kfree(data);
-	} else if (cpufreq_driver->target) {
+	} else if (target) {
 		__cpufreq_governor(data, CPUFREQ_GOV_START);
 		__cpufreq_governor(data, CPUFREQ_GOV_LIMITS);
 	}
@@ -1157,10 +1224,18 @@  static void cpufreq_out_of_sync(unsigned int cpu, unsigned int old_freq,
 unsigned int cpufreq_quick_get(unsigned int cpu)
 {
 	struct cpufreq_policy *policy;
+	struct cpufreq_driver *driver;
+	unsigned int (*get)(unsigned int cpu);
 	unsigned int ret_freq = 0;
 
-	if (cpufreq_driver && cpufreq_driver->setpolicy && cpufreq_driver->get)
-		return cpufreq_driver->get(cpu);
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
+	if (driver && driver->setpolicy && driver->get) {
+		get = driver->get;
+		rcu_read_unlock();
+		return get(cpu);
+	}
+	rcu_read_unlock();
 
 	policy = cpufreq_cpu_get(cpu);
 	if (policy) {
@@ -1196,15 +1271,26 @@  EXPORT_SYMBOL(cpufreq_quick_get_max);
 static unsigned int __cpufreq_get(unsigned int cpu)
 {
 	struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
+	struct cpufreq_driver *driver;
+	unsigned int (*get)(unsigned int cpu);
 	unsigned int ret_freq = 0;
+	u8 flags;
+
 
-	if (!cpufreq_driver->get)
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
+	if (!driver->get) {
+		rcu_read_unlock();
 		return ret_freq;
+	}
+	flags = driver->flags;
+	get = driver->get;
+	rcu_read_unlock();
 
-	ret_freq = cpufreq_driver->get(cpu);
+	ret_freq = get(cpu);
 
 	if (ret_freq && policy->cur &&
-		!(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
+		!(flags & CPUFREQ_CONST_LOOPS)) {
 		/* verify no discrepancy between actual and
 					saved value exists */
 		if (unlikely(ret_freq != policy->cur)) {
@@ -1260,6 +1346,7 @@  static struct subsys_interface cpufreq_interface = {
  */
 static int cpufreq_bp_suspend(void)
 {
+	int (*suspend)(struct cpufreq_policy *policy);
 	int ret = 0;
 
 	int cpu = smp_processor_id();
@@ -1272,8 +1359,11 @@  static int cpufreq_bp_suspend(void)
 	if (!cpu_policy)
 		return 0;
 
-	if (cpufreq_driver->suspend) {
-		ret = cpufreq_driver->suspend(cpu_policy);
+	rcu_read_lock();
+	suspend = rcu_dereference(cpufreq_driver)->suspend;
+	rcu_read_unlock();
+	if (suspend) {
+		ret = suspend(cpu_policy);
 		if (ret)
 			printk(KERN_ERR "cpufreq: suspend failed in ->suspend "
 					"step on CPU %u\n", cpu_policy->cpu);
@@ -1299,6 +1389,7 @@  static int cpufreq_bp_suspend(void)
 static void cpufreq_bp_resume(void)
 {
 	int ret = 0;
+	int (*resume)(struct cpufreq_policy *policy);
 
 	int cpu = smp_processor_id();
 	struct cpufreq_policy *cpu_policy;
@@ -1310,8 +1401,12 @@  static void cpufreq_bp_resume(void)
 	if (!cpu_policy)
 		return;
 
-	if (cpufreq_driver->resume) {
-		ret = cpufreq_driver->resume(cpu_policy);
+	rcu_read_lock();
+	resume = rcu_dereference(cpufreq_driver)->resume;
+	rcu_read_unlock();
+
+	if (resume) {
+		ret = resume(cpu_policy);
 		if (ret) {
 			printk(KERN_ERR "cpufreq: resume failed in ->resume "
 					"step on CPU %u\n", cpu_policy->cpu);
@@ -1338,10 +1433,14 @@  static struct syscore_ops cpufreq_syscore_ops = {
  */
 const char *cpufreq_get_current_driver(void)
 {
-	if (cpufreq_driver)
-		return cpufreq_driver->name;
-
-	return NULL;
+	struct cpufreq_driver *driver;
+	const char *name = NULL;
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
+	if (driver)
+		name = driver->name;
+	rcu_read_unlock();
+	return name;
 }
 EXPORT_SYMBOL_GPL(cpufreq_get_current_driver);
 
@@ -1435,6 +1534,9 @@  int __cpufreq_driver_target(struct cpufreq_policy *policy,
 {
 	int retval = -EINVAL;
 	unsigned int old_target_freq = target_freq;
+	int (*target)(struct cpufreq_policy *policy,
+		      unsigned int target_freq,
+		      unsigned int relation);
 
 	if (cpufreq_disabled())
 		return -ENODEV;
@@ -1451,8 +1553,11 @@  int __cpufreq_driver_target(struct cpufreq_policy *policy,
 	if (target_freq == policy->cur)
 		return 0;
 
-	if (cpufreq_driver->target)
-		retval = cpufreq_driver->target(policy, target_freq, relation);
+	rcu_read_lock();
+	target = rcu_dereference(cpufreq_driver)->target;
+	rcu_read_unlock();
+	if (target)
+		retval = target(policy, target_freq, relation);
 
 	return retval;
 }
@@ -1485,18 +1590,24 @@  EXPORT_SYMBOL_GPL(cpufreq_driver_target);
 int __cpufreq_driver_getavg(struct cpufreq_policy *policy, unsigned int cpu)
 {
 	int ret = 0;
+	unsigned int (*getavg)(struct cpufreq_policy *policy,
+			       unsigned int cpu);
 
 	if (cpufreq_disabled())
 		return ret;
 
-	if (!cpufreq_driver->getavg)
+	rcu_read_lock();
+	getavg = rcu_dereference(cpufreq_driver)->getavg;
+	rcu_read_unlock();
+
+	if (!getavg)
 		return 0;
 
 	policy = cpufreq_cpu_get(policy->cpu);
 	if (!policy)
 		return -EINVAL;
 
-	ret = cpufreq_driver->getavg(policy, cpu);
+	ret = getavg(policy, cpu);
 
 	cpufreq_cpu_put(policy);
 	return ret;
@@ -1652,6 +1763,9 @@  static int __cpufreq_set_policy(struct cpufreq_policy *data,
 				struct cpufreq_policy *policy)
 {
 	int ret = 0;
+	struct cpufreq_driver *driver;
+	int (*verify)(struct cpufreq_policy *policy);
+	int (*setpolicy)(struct cpufreq_policy *policy);
 
 	pr_debug("setting new policy for CPU %u: %u - %u kHz\n", policy->cpu,
 		policy->min, policy->max);
@@ -1665,7 +1779,13 @@  static int __cpufreq_set_policy(struct cpufreq_policy *data,
 	}
 
 	/* verify the cpu speed can be set within this limit */
-	ret = cpufreq_driver->verify(policy);
+	rcu_read_lock();
+	driver = rcu_dereference(cpufreq_driver);
+	verify = driver->verify;
+	setpolicy = driver->setpolicy;
+	rcu_read_unlock();
+
+	ret = verify(policy);
 	if (ret)
 		goto error_out;
 
@@ -1679,7 +1799,7 @@  static int __cpufreq_set_policy(struct cpufreq_policy *data,
 
 	/* verify the cpu speed can be set within this limit,
 	   which might be different to the first one */
-	ret = cpufreq_driver->verify(policy);
+	ret = verify(policy);
 	if (ret)
 		goto error_out;
 
@@ -1693,10 +1813,10 @@  static int __cpufreq_set_policy(struct cpufreq_policy *data,
 	pr_debug("new min and max freqs are %u - %u kHz\n",
 					data->min, data->max);
 
-	if (cpufreq_driver->setpolicy) {
+	if (setpolicy) {
 		data->policy = policy->policy;
 		pr_debug("setting range\n");
-		ret = cpufreq_driver->setpolicy(policy);
+		ret = setpolicy(policy);
 	} else {
 		if (policy->governor != data->governor) {
 			/* save old, working values */
@@ -1743,6 +1863,11 @@  int cpufreq_update_policy(unsigned int cpu)
 {
 	struct cpufreq_policy *data = cpufreq_cpu_get(cpu);
 	struct cpufreq_policy policy;
+	struct cpufreq_driver *driver;
+	unsigned int (*get)(unsigned int cpu);
+	int (*target)(struct cpufreq_policy *policy,
+		      unsigned int target_freq,
+		      unsigned int relation);
 	int ret;
 
 	if (!data) {
@@ -1764,13 +1889,18 @@  int cpufreq_update_policy(unsigned int cpu)
 
 	/* BIOS might change freq behind our back
 	  -> ask driver for current freq and notify governors about a change */
-	if (cpufreq_driver->get) {
-		policy.cur = cpufreq_driver->get(cpu);
+	rcu_read_lock();
+	driver = rcu_access_pointer(cpufreq_driver);
+	get = driver->get;
+	target = driver->target;
+	rcu_read_unlock();
+	if (get) {
+		policy.cur = get(cpu);
 		if (!data->cur) {
 			pr_debug("Driver did not initialize current freq");
 			data->cur = policy.cur;
 		} else {
-			if (data->cur != policy.cur && cpufreq_driver->target)
+			if (data->cur != policy.cur && target)
 				cpufreq_out_of_sync(cpu, data->cur,
 								policy.cur);
 		}
@@ -1849,18 +1979,19 @@  int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 		driver_data->flags |= CPUFREQ_CONST_LOOPS;
 
 	spin_lock_irqsave(&cpufreq_driver_lock, flags);
-	if (cpufreq_driver) {
+	if (rcu_access_pointer(cpufreq_driver)) {
 		spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
 		return -EBUSY;
 	}
-	cpufreq_driver = driver_data;
+	rcu_assign_pointer(cpufreq_driver, driver_data);
 	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	synchronize_rcu();
 
 	ret = subsys_interface_register(&cpufreq_interface);
 	if (ret)
 		goto err_null_driver;
 
-	if (!(cpufreq_driver->flags & CPUFREQ_STICKY)) {
+	if (!(driver_data->flags & CPUFREQ_STICKY)) {
 		int i;
 		ret = -ENODEV;
 
@@ -1887,8 +2018,9 @@  err_if_unreg:
 	subsys_interface_unregister(&cpufreq_interface);
 err_null_driver:
 	spin_lock_irqsave(&cpufreq_driver_lock, flags);
-	cpufreq_driver = NULL;
+	rcu_assign_pointer(cpufreq_driver, NULL);
 	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	synchronize_rcu();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(cpufreq_register_driver);
@@ -1905,9 +2037,15 @@  EXPORT_SYMBOL_GPL(cpufreq_register_driver);
 int cpufreq_unregister_driver(struct cpufreq_driver *driver)
 {
 	unsigned long flags;
+	struct cpufreq_driver *old_driver;
 
-	if (!cpufreq_driver || (driver != cpufreq_driver))
+	rcu_read_lock();
+	old_driver = rcu_access_pointer(cpufreq_driver);
+	if (!old_driver || (driver != old_driver)) {
+		rcu_read_unlock();
 		return -EINVAL;
+	}
+	rcu_read_unlock();
 
 	pr_debug("unregistering driver %s\n", driver->name);
 
@@ -1917,6 +2055,7 @@  int cpufreq_unregister_driver(struct cpufreq_driver *driver)
 	spin_lock_irqsave(&cpufreq_driver_lock, flags);
 	cpufreq_driver = NULL;
 	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	synchronize_rcu();
 
 	return 0;
 }