[PATCH] cpufreq: convert the cpufreq_driver to use the rcu

From: Nathan Zimmer
Date: Wed Apr 03 2013 - 11:03:18 EST

We eventually would like to remove the rwlock cpufreq_driver_lock or convert
it back to a spinlock and protect the read sections with RCU. The first step in
that is moving the cpufreq_driver to use the RCU for its read areas.
I don't see an easy wasy to protect the cpufreq_cpu_data structure with the
RCU, so I am leaving it with the rwlock for now since under certain configs
__cpufreq_cpu_get is hot spot with 256+ cores.

Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
Signed-off-by: Nathan Zimmer <nzimmer@xxxxxxx>
---
drivers/cpufreq/cpufreq.c | 278 ++++++++++++++++++++++++++++++++++------------
1 file changed, 207 insertions(+), 71 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 85963fc..e89506c 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -39,7 +39,7 @@
* 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_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 */
@@ -130,26 +130,33 @@ static DEFINE_MUTEX(cpufreq_governor_mutex);

bool have_governor_per_policy(void)
{
- return cpufreq_driver->have_governor_per_policy;
+ bool have_governor;
+ rcu_read_lock();
+ have_governor = rcu_dereference(cpufreq_driver)->have_governor_per_policy;
+ rcu_read_unlock();
+ return have_governor;
}

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 */
- read_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;

+ read_lock_irqsave(&cpufreq_driver_lock, flags);

/* get the CPU */
data = per_cpu(cpufreq_cpu_data, cpu);
@@ -161,12 +168,14 @@ static struct cpufreq_policy *__cpufreq_cpu_get(unsigned int cpu, bool sysfs)
goto err_out_put_module;

read_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ rcu_read_unlock();
return data;

err_out_put_module:
- module_put(cpufreq_driver->owner);
-err_out_unlock:
+ module_put(driver->owner);
read_unlock_irqrestore(&cpufreq_driver_lock, flags);
+err_out_unlock:
+ rcu_read_unlock();
err_out:
return NULL;
}
@@ -189,7 +198,9 @@ 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)
@@ -267,7 +278,9 @@ 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);

@@ -282,7 +295,7 @@ 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"
@@ -334,11 +347,21 @@ 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;
+ bool has_setpolicy;
+ bool has_target;
+
+ rcu_read_lock();
+ driver = rcu_dereference(cpufreq_driver);
+ if (!driver) {
+ rcu_read_unlock();
goto out;
+ }
+ has_setpolicy = driver->setpolicy ? true : false;
+ has_target = driver->target ? true : false;
+ rcu_read_unlock();

- if (cpufreq_driver->setpolicy) {
+ if (has_setpolicy) {
if (!strnicmp(str_governor, "performance", CPUFREQ_NAME_LEN)) {
*policy = CPUFREQ_POLICY_PERFORMANCE;
err = 0;
@@ -347,7 +370,7 @@ static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
*policy = CPUFREQ_POLICY_POWERSAVE;
err = 0;
}
- } else if (cpufreq_driver->target) {
+ } else if (has_target) {
struct cpufreq_governor *t;

mutex_lock(&cpufreq_governor_mutex);
@@ -498,7 +521,11 @@ 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);
}

/**
@@ -510,10 +537,13 @@ 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))
@@ -591,9 +621,15 @@ 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);
}
@@ -736,6 +772,7 @@ static int cpufreq_add_dev_interface(unsigned int cpu,
{
struct cpufreq_policy new_policy;
struct freq_attr **drv_attr;
+ struct cpufreq_driver *driver;
unsigned long flags;
int ret = 0;
unsigned int j;
@@ -747,28 +784,31 @@ 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();

write_lock_irqsave(&cpufreq_driver_lock, flags);
for_each_cpu(j, policy->cpus) {
@@ -791,12 +831,20 @@ static int cpufreq_add_dev_interface(unsigned int cpu,
policy->user_policy.governor = policy->governor;

if (ret) {
+ int (*exit)(struct cpufreq_policy *policy);
+
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);
@@ -854,6 +902,8 @@ 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;
@@ -888,10 +938,15 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
#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)
@@ -916,7 +971,7 @@ 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;
@@ -951,7 +1006,9 @@ 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;
@@ -973,7 +1030,9 @@ 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;
}
@@ -1007,9 +1066,12 @@ 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;
+ bool has_target;
+ int (*exit)(struct cpufreq_policy *policy);

pr_debug("%s: unregistering CPU %u\n", __func__, cpu);

@@ -1025,14 +1087,19 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
return -EINVAL;
}

- if (cpufreq_driver->target)
+ rcu_read_lock();
+ driver = rcu_dereference(cpufreq_driver);
+ has_target = driver->target ? true : false;
+ exit = driver->exit;
+ if (has_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);
@@ -1091,13 +1158,13 @@ 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 (has_target) {
__cpufreq_governor(data, CPUFREQ_GOV_START);
__cpufreq_governor(data, CPUFREQ_GOV_LIMITS);
}
@@ -1164,10 +1231,18 @@ 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) {
@@ -1203,15 +1278,26 @@ 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)) {
@@ -1267,6 +1353,7 @@ 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();
@@ -1279,8 +1366,11 @@ 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);
@@ -1306,6 +1396,7 @@ 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;
@@ -1317,8 +1408,12 @@ 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);
@@ -1345,10 +1440,14 @@ 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);

@@ -1442,6 +1541,9 @@ 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;
@@ -1458,8 +1560,11 @@ 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;
}
@@ -1492,18 +1597,24 @@ 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;
@@ -1661,6 +1772,9 @@ static int __cpufreq_set_policy(struct cpufreq_policy *data,
struct cpufreq_policy *policy)
{
int ret = 0, failed = 1;
+ 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);
@@ -1674,7 +1788,13 @@ 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;

@@ -1688,7 +1808,7 @@ 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;

@@ -1702,10 +1822,10 @@ 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 */
@@ -1765,6 +1885,11 @@ 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) {
@@ -1786,13 +1911,18 @@ 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);
}
@@ -1855,7 +1985,6 @@ static struct notifier_block __refdata cpufreq_cpu_notifier = {
*/
int cpufreq_register_driver(struct cpufreq_driver *driver_data)
{
- unsigned long flags;
int ret;

if (cpufreq_disabled())
@@ -1869,20 +1998,20 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)

if (driver_data->setpolicy)
driver_data->flags |= CPUFREQ_CONST_LOOPS;
-
+
write_lock_irqsave(&cpufreq_driver_lock, flags);
- if (cpufreq_driver) {
- write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ if (rcu_access_pointer(cpufreq_driver)) {
return -EBUSY;
}
- cpufreq_driver = driver_data;
+ rcu_assign_pointer(cpufreq_driver, driver_data);;
write_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;

@@ -1909,8 +2038,9 @@ err_if_unreg:
subsys_interface_unregister(&cpufreq_interface);
err_null_driver:
write_lock_irqsave(&cpufreq_driver_lock, flags);
- cpufreq_driver = NULL;
+ rcu_assign_pointer(cpufreq_driver, NULL);
write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ synchronize_rcu();
return ret;
}
EXPORT_SYMBOL_GPL(cpufreq_register_driver);
@@ -1926,10 +2056,15 @@ 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);

@@ -1937,8 +2072,9 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver)
unregister_hotcpu_notifier(&cpufreq_cpu_notifier);

write_lock_irqsave(&cpufreq_driver_lock, flags);
- cpufreq_driver = NULL;
+ rcu_assign_pointer(cpufreq_driver, NULL);
write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ synchronize_rcu();

return 0;
}
--
1.8.1.2

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