cpufreq: Revert incorrect commit 5800043

Commit 5800043 (cpufreq: convert cpufreq_driver to using RCU) causes
the following call trace to be spit on boot:

 BUG: sleeping function called from invalid context at /scratch/rafael/work/linux-pm/mm/slab.c:3179
 in_atomic(): 0, irqs_disabled(): 0, pid: 292, name: systemd-udevd
 2 locks held by systemd-udevd/292:
  #0:  (subsys mutex){+.+.+.}, at: [<ffffffff8146851a>] subsys_interface_register+0x4a/0xe0
  #1:  (rcu_read_lock){.+.+.+}, at: [<ffffffff81538210>] cpufreq_add_dev_interface+0x60/0x5e0
 Pid: 292, comm: systemd-udevd Not tainted 3.9.0-rc8+ #323
 Call Trace:
  [<ffffffff81072c90>] __might_sleep+0x140/0x1f0
  [<ffffffff811581c2>] kmem_cache_alloc+0x42/0x2b0
  [<ffffffff811e7179>] sysfs_new_dirent+0x59/0x130
  [<ffffffff811e63cb>] sysfs_add_file_mode+0x6b/0x110
  [<ffffffff81538210>] ? cpufreq_add_dev_interface+0x60/0x5e0
  [<ffffffff810a3254>] ? __lock_is_held+0x54/0x80
  [<ffffffff811e647d>] sysfs_add_file+0xd/0x10
  [<ffffffff811e6541>] sysfs_create_file+0x21/0x30
  [<ffffffff81538280>] cpufreq_add_dev_interface+0xd0/0x5e0
  [<ffffffff81538210>] ? cpufreq_add_dev_interface+0x60/0x5e0
  [<ffffffffa000337f>] ? acpi_processor_get_platform_limit+0x32/0xbb [processor]
  [<ffffffffa022f540>] ? do_drv_write+0x70/0x70 [acpi_cpufreq]
  [<ffffffff810a3254>] ? __lock_is_held+0x54/0x80
  [<ffffffff8106c97e>] ? up_read+0x1e/0x40
  [<ffffffff8106e632>] ? __blocking_notifier_call_chain+0x72/0xc0
  [<ffffffff81538dbd>] cpufreq_add_dev+0x62d/0xae0
  [<ffffffff815389b8>] ? cpufreq_add_dev+0x228/0xae0
  [<ffffffff81468569>] subsys_interface_register+0x99/0xe0
  [<ffffffffa014d000>] ? 0xffffffffa014cfff
  [<ffffffff81535d5d>] cpufreq_register_driver+0x9d/0x200
  [<ffffffffa014d000>] ? 0xffffffffa014cfff
  [<ffffffffa014d0e9>] acpi_cpufreq_init+0xe9/0x1000 [acpi_cpufreq]
  [<ffffffff810002fa>] do_one_initcall+0x11a/0x170
  [<ffffffff810b4b87>] load_module+0x1cf7/0x2920
  [<ffffffff81322580>] ? ddebug_proc_open+0xb0/0xb0
  [<ffffffff816baee0>] ? retint_restore_args+0xe/0xe
  [<ffffffff810b5887>] sys_init_module+0xd7/0x120
  [<ffffffff816bb6d2>] system_call_fastpath+0x16/0x1b

which is quite obvious, because that commit put (multiple instances
of) sysfs_create_file() under rcu_read_lock()/rcu_read_unlock(),
although sysfs_create_file() may cause memory to be allocated with
GFP_KERNEL and that may sleep, which is not permitted in RCU read
critical section.

Revert the buggy commit altogether along with some changes on top
of it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 69 insertions, 214 deletions

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index a6f65954b0ab..1b8a48eaf90f 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 __rcu *cpufreq_driver;
+static struct cpufreq_driver *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 */
@@ -130,34 +130,26 @@ static DEFINE_MUTEX(cpufreq_governor_mutex);
 
 bool have_governor_per_policy(void)
 {
-        bool have_governor_per_policy;
-        rcu_read_lock();
-        have_governor_per_policy =
-                rcu_dereference(cpufreq_driver)->have_governor_per_policy;
-        rcu_read_unlock();
-        return have_governor_per_policy;
+        return cpufreq_driver->have_governor_per_policy;
 }
 
 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 */
-        rcu_read_lock();
-        driver = rcu_dereference(cpufreq_driver);
+        read_lock_irqsave(&cpufreq_driver_lock, flags);
 
-        if (!driver)
+        if (!cpufreq_driver)
                 goto err_out_unlock;
 
-        if (!try_module_get(driver->owner))
+        if (!try_module_get(cpufreq_driver->owner))
                 goto err_out_unlock;
 
-        read_lock_irqsave(&cpufreq_driver_lock, flags);
 
         /* get the CPU */
         data = per_cpu(cpufreq_cpu_data, cpu);
@@ -169,14 +161,12 @@ 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(driver->owner);
-        read_unlock_irqrestore(&cpufreq_driver_lock, flags);
+        module_put(cpufreq_driver->owner);
 err_out_unlock:
-        rcu_read_unlock();
+        read_unlock_irqrestore(&cpufreq_driver_lock, flags);
 err_out:
         return NULL;
 }
@@ -199,9 +189,7 @@ static void __cpufreq_cpu_put(struct cpufreq_policy *data, bool sysfs)
 {
         if (!sysfs)
                 kobject_put(&data->kobj);
-        rcu_read_lock();
-        module_put(rcu_dereference(cpufreq_driver)->owner);
-        rcu_read_unlock();
+        module_put(cpufreq_driver->owner);
 }
 
 void cpufreq_cpu_put(struct cpufreq_policy *data)
@@ -269,9 +257,7 @@ void __cpufreq_notify_transition(struct cpufreq_policy *policy,
         if (cpufreq_disabled())
                 return;
 
-        rcu_read_lock();
-        freqs->flags = rcu_dereference(cpufreq_driver)->flags;
-        rcu_read_unlock();
+        freqs->flags = cpufreq_driver->flags;
         pr_debug("notification %u of frequency transition to %u kHz\n",
                 state, freqs->new);
 
@@ -282,7 +268,7 @@ void __cpufreq_notify_transition(struct cpufreq_policy *policy,
                  * which is not equal to what the cpufreq core thinks is
                  * "old frequency".
                  */
-                if (!(freqs->flags & CPUFREQ_CONST_LOOPS)) {
+                if (!(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
                         if ((policy) && (policy->cpu == freqs->cpu) &&
                             (policy->cur) && (policy->cur != freqs->old)) {
                                 pr_debug("Warning: CPU frequency is"
@@ -348,21 +334,11 @@ static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
                                 struct cpufreq_governor **governor)
 {
         int err = -EINVAL;
-        struct cpufreq_driver *driver;
-        bool has_setpolicy;
-        bool has_target;
-
-        rcu_read_lock();
-        driver = rcu_dereference(cpufreq_driver);
-        if (!driver) {
-                rcu_read_unlock();
+
+        if (!cpufreq_driver)
                 goto out;
-        }
-        has_setpolicy = driver->setpolicy ? true : false;
-        has_target = driver->target ? true : false;
-        rcu_read_unlock();
 
-        if (has_setpolicy) {
+        if (cpufreq_driver->setpolicy) {
                 if (!strnicmp(str_governor, "performance", CPUFREQ_NAME_LEN)) {
                         *policy = CPUFREQ_POLICY_PERFORMANCE;
                         err = 0;
@@ -371,7 +347,7 @@ static int cpufreq_parse_governor(char *str_governor, unsigned int *policy,
                         *policy = CPUFREQ_POLICY_POWERSAVE;
                         err = 0;
                 }
-        } else if (has_target) {
+        } else if (cpufreq_driver->target) {
                 struct cpufreq_governor *t;
 
                 mutex_lock(&cpufreq_governor_mutex);
@@ -522,12 +498,7 @@ static ssize_t store_scaling_governor(struct cpufreq_policy *policy,
  */
 static ssize_t show_scaling_driver(struct cpufreq_policy *policy, char *buf)
 {
-        ssize_t size;
-        rcu_read_lock();
-        size = scnprintf(buf, CPUFREQ_NAME_PLEN, "%s\n",
-                rcu_dereference(cpufreq_driver)->name);
-        rcu_read_unlock();
-        return size;
+        return scnprintf(buf, CPUFREQ_NAME_PLEN, "%s\n", cpufreq_driver->name);
 }
 
 /**
@@ -539,13 +510,10 @@ static ssize_t show_scaling_available_governors(struct cpufreq_policy *policy,
         ssize_t i = 0;
         struct cpufreq_governor *t;
 
-        rcu_read_lock();
-        if (!rcu_dereference(cpufreq_driver)->target) {
-                rcu_read_unlock();
+        if (!cpufreq_driver->target) {
                 i += sprintf(buf, "performance powersave");
                 goto out;
         }
-        rcu_read_unlock();
 
         list_for_each_entry(t, &cpufreq_governor_list, governor_list) {
                 if (i >= (ssize_t) ((PAGE_SIZE / sizeof(char))
@@ -623,15 +591,9 @@ 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;
-
-        rcu_read_lock();
-        bios_limit = rcu_dereference(cpufreq_driver)->bios_limit;
-        rcu_read_unlock();
-
-        if (bios_limit) {
-                ret = bios_limit(policy->cpu, &limit);
+        if (cpufreq_driver->bios_limit) {
+                ret = cpufreq_driver->bios_limit(policy->cpu, &limit);
                 if (!ret)
                         return sprintf(buf, "%u\n", limit);
         }
@@ -774,7 +736,6 @@ 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;
@@ -786,31 +747,28 @@ static int cpufreq_add_dev_interface(unsigned int cpu,
                 return ret;
 
         /* set up files for this cpu device */
-        rcu_read_lock();
-        driver = rcu_dereference(cpufreq_driver);
-        drv_attr = driver->attr;
+        drv_attr = cpufreq_driver->attr;
         while ((drv_attr) && (*drv_attr)) {
                 ret = sysfs_create_file(&policy->kobj, &((*drv_attr)->attr));
                 if (ret)
-                        goto err_out_unlock;
+                        goto err_out_kobj_put;
                 drv_attr++;
         }
-        if (driver->get) {
+        if (cpufreq_driver->get) {
                 ret = sysfs_create_file(&policy->kobj, &cpuinfo_cur_freq.attr);
                 if (ret)
-                        goto err_out_unlock;
+                        goto err_out_kobj_put;
         }
-        if (driver->target) {
+        if (cpufreq_driver->target) {
                 ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
                 if (ret)
-                        goto err_out_unlock;
+                        goto err_out_kobj_put;
         }
-        if (driver->bios_limit) {
+        if (cpufreq_driver->bios_limit) {
                 ret = sysfs_create_file(&policy->kobj, &bios_limit.attr);
                 if (ret)
-                        goto err_out_unlock;
+                        goto err_out_kobj_put;
         }
-        rcu_read_unlock();
 
         write_lock_irqsave(&cpufreq_driver_lock, flags);
         for_each_cpu(j, policy->cpus) {
@@ -833,20 +791,12 @@ 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");
-                rcu_read_lock();
-                exit = rcu_dereference(cpufreq_driver)->exit;
-                rcu_read_unlock();
-                if (exit)
-                        exit(policy);
-
+                if (cpufreq_driver->exit)
+                        cpufreq_driver->exit(policy);
         }
         return ret;
 
-err_out_unlock:
-        rcu_read_unlock();
 err_out_kobj_put:
         kobject_put(&policy->kobj);
         wait_for_completion(&policy->kobj_unregister);
@@ -858,16 +808,12 @@ static int cpufreq_add_policy_cpu(unsigned int cpu, unsigned int sibling,
                                   struct device *dev)
 {
         struct cpufreq_policy *policy;
-        int ret = 0, has_target = 0;
+        int ret = 0, has_target = !!cpufreq_driver->target;
         unsigned long flags;
 
         policy = cpufreq_cpu_get(sibling);
         WARN_ON(!policy);
 
-        rcu_read_lock();
-        has_target = !!rcu_dereference(cpufreq_driver)->target;
-        rcu_read_unlock();
-
         if (has_target)
                 __cpufreq_governor(policy, CPUFREQ_GOV_STOP);
 
@@ -911,8 +857,6 @@ 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;
@@ -947,15 +891,10 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
 #endif
 #endif
 
-        rcu_read_lock();
-        driver = rcu_dereference(cpufreq_driver);
-        if (!try_module_get(driver->owner)) {
-                rcu_read_unlock();
+        if (!try_module_get(cpufreq_driver->owner)) {
                 ret = -EINVAL;
                 goto module_out;
         }
-        init = driver->init;
-        rcu_read_unlock();
 
         policy = kzalloc(sizeof(struct cpufreq_policy), GFP_KERNEL);
         if (!policy)
@@ -980,7 +919,7 @@ 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 = init(policy);
+        ret = cpufreq_driver->init(policy);
         if (ret) {
                 pr_debug("initialization failed\n");
                 goto err_set_policy_cpu;
@@ -1015,9 +954,7 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
                 goto err_out_unregister;
 
         kobject_uevent(&policy->kobj, KOBJ_ADD);
-        rcu_read_lock();
-        module_put(rcu_dereference(cpufreq_driver)->owner);
-        rcu_read_unlock();
+        module_put(cpufreq_driver->owner);
         pr_debug("initialization complete\n");
 
         return 0;
@@ -1039,9 +976,7 @@ err_free_cpumask:
 err_free_policy:
         kfree(policy);
 nomem_out:
-        rcu_read_lock();
-        module_put(rcu_dereference(cpufreq_driver)->owner);
-        rcu_read_unlock();
+        module_put(cpufreq_driver->owner);
 module_out:
         return ret;
 }
@@ -1075,12 +1010,9 @@ 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);
 
@@ -1096,19 +1028,14 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
                 return -EINVAL;
         }
 
-        rcu_read_lock();
-        driver = rcu_dereference(cpufreq_driver);
-        has_target = driver->target ? true : false;
-        exit = driver->exit;
-        if (has_target)
+        if (cpufreq_driver->target)
                 __cpufreq_governor(data, CPUFREQ_GOV_STOP);
 
 #ifdef CONFIG_HOTPLUG_CPU
-        if (!driver->setpolicy)
+        if (!cpufreq_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);
@@ -1153,7 +1080,7 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
 
         /* If cpu is last user of policy, free policy */
         if (cpus == 1) {
-                if (has_target)
+                if (cpufreq_driver->target)
                         __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT);
 
                 lock_policy_rwsem_read(cpu);
@@ -1170,13 +1097,13 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
                 wait_for_completion(cmp);
                 pr_debug("wait complete\n");
 
-                if (exit)
-                        exit(data);
+                if (cpufreq_driver->exit)
+                        cpufreq_driver->exit(data);
 
                 free_cpumask_var(data->related_cpus);
                 free_cpumask_var(data->cpus);
                 kfree(data);
-        } else if (has_target) {
+        } else if (cpufreq_driver->target) {
                 __cpufreq_governor(data, CPUFREQ_GOV_START);
                 __cpufreq_governor(data, CPUFREQ_GOV_LIMITS);
         }
@@ -1250,18 +1177,10 @@ 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;
 
-        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();
+        if (cpufreq_driver && cpufreq_driver->setpolicy && cpufreq_driver->get)
+                return cpufreq_driver->get(cpu);
 
         policy = cpufreq_cpu_get(cpu);
         if (policy) {
@@ -1297,26 +1216,15 @@ 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;
 
-
-        rcu_read_lock();
-        driver = rcu_dereference(cpufreq_driver);
-        if (!driver->get) {
-                rcu_read_unlock();
+        if (!cpufreq_driver->get)
                 return ret_freq;
-        }
-        flags = driver->flags;
-        get = driver->get;
-        rcu_read_unlock();
 
-        ret_freq = get(cpu);
+        ret_freq = cpufreq_driver->get(cpu);
 
         if (ret_freq && policy->cur &&
-                !(flags & CPUFREQ_CONST_LOOPS)) {
+                !(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
                 /* verify no discrepancy between actual and
                                         saved value exists */
                 if (unlikely(ret_freq != policy->cur)) {
@@ -1372,7 +1280,6 @@ 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();
@@ -1385,11 +1292,8 @@ static int cpufreq_bp_suspend(void)
         if (!cpu_policy)
                 return 0;
 
-        rcu_read_lock();
-        suspend = rcu_dereference(cpufreq_driver)->suspend;
-        rcu_read_unlock();
-        if (suspend) {
-                ret = suspend(cpu_policy);
+        if (cpufreq_driver->suspend) {
+                ret = cpufreq_driver->suspend(cpu_policy);
                 if (ret)
                         printk(KERN_ERR "cpufreq: suspend failed in ->suspend "
                                         "step on CPU %u\n", cpu_policy->cpu);
@@ -1415,7 +1319,6 @@ 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;
@@ -1427,12 +1330,8 @@ static void cpufreq_bp_resume(void)
         if (!cpu_policy)
                 return;
 
-        rcu_read_lock();
-        resume = rcu_dereference(cpufreq_driver)->resume;
-        rcu_read_unlock();
-
-        if (resume) {
-                ret = resume(cpu_policy);
+        if (cpufreq_driver->resume) {
+                ret = cpufreq_driver->resume(cpu_policy);
                 if (ret) {
                         printk(KERN_ERR "cpufreq: resume failed in ->resume "
                                         "step on CPU %u\n", cpu_policy->cpu);
@@ -1459,14 +1358,10 @@ static struct syscore_ops cpufreq_syscore_ops = {
  */
 const char *cpufreq_get_current_driver(void)
 {
-        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;
+        if (cpufreq_driver)
+                return cpufreq_driver->name;
+
+        return NULL;
 }
 EXPORT_SYMBOL_GPL(cpufreq_get_current_driver);
 
@@ -1560,9 +1455,6 @@ 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;
@@ -1579,11 +1471,8 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
         if (target_freq == policy->cur)
                 return 0;
 
-        rcu_read_lock();
-        target = rcu_dereference(cpufreq_driver)->target;
-        rcu_read_unlock();
-        if (target)
-                retval = target(policy, target_freq, relation);
+        if (cpufreq_driver->target)
+                retval = cpufreq_driver->target(policy, target_freq, relation);
 
         return retval;
 }
@@ -1616,24 +1505,18 @@ 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;
 
-        rcu_read_lock();
-        getavg = rcu_dereference(cpufreq_driver)->getavg;
-        rcu_read_unlock();
-
-        if (!getavg)
+        if (!cpufreq_driver->getavg)
                 return 0;
 
         policy = cpufreq_cpu_get(policy->cpu);
         if (!policy)
                 return -EINVAL;
 
-        ret = getavg(policy, cpu);
+        ret = cpufreq_driver->getavg(policy, cpu);
 
         cpufreq_cpu_put(policy);
         return ret;
@@ -1791,9 +1674,6 @@ 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);
@@ -1807,13 +1687,7 @@ static int __cpufreq_set_policy(struct cpufreq_policy *data,
         }
 
         /* verify the cpu speed can be set within this limit */
-        rcu_read_lock();
-        driver = rcu_dereference(cpufreq_driver);
-        verify = driver->verify;
-        setpolicy = driver->setpolicy;
-        rcu_read_unlock();
-
-        ret = verify(policy);
+        ret = cpufreq_driver->verify(policy);
         if (ret)
                 goto error_out;
 
@@ -1827,7 +1701,7 @@ 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 = verify(policy);
+        ret = cpufreq_driver->verify(policy);
         if (ret)
                 goto error_out;
 
@@ -1841,10 +1715,10 @@ 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 (setpolicy) {
+        if (cpufreq_driver->setpolicy) {
                 data->policy = policy->policy;
                 pr_debug("setting range\n");
-                ret = setpolicy(policy);
+                ret = cpufreq_driver->setpolicy(policy);
         } else {
                 if (policy->governor != data->governor) {
                         /* save old, working values */
@@ -1904,11 +1778,6 @@ 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) {
@@ -1930,18 +1799,13 @@ 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 */
-        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 (cpufreq_driver->get) {
+                policy.cur = cpufreq_driver->get(cpu);
                 if (!data->cur) {
                         pr_debug("Driver did not initialize current freq");
                         data->cur = policy.cur;
                 } else {
-                        if (data->cur != policy.cur && target)
+                        if (data->cur != policy.cur && cpufreq_driver->target)
                                 cpufreq_out_of_sync(cpu, data->cur,
                                                                 policy.cur);
                 }
@@ -2020,19 +1884,18 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
                 driver_data->flags |= CPUFREQ_CONST_LOOPS;
 
         write_lock_irqsave(&cpufreq_driver_lock, flags);
-        if (rcu_access_pointer(cpufreq_driver)) {
+        if (cpufreq_driver) {
                 write_unlock_irqrestore(&cpufreq_driver_lock, flags);
                 return -EBUSY;
         }
-        rcu_assign_pointer(cpufreq_driver, driver_data);
+        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 (!(driver_data->flags & CPUFREQ_STICKY)) {
+        if (!(cpufreq_driver->flags & CPUFREQ_STICKY)) {
                 int i;
                 ret = -ENODEV;
 
@@ -2059,9 +1922,8 @@ err_if_unreg:
         subsys_interface_unregister(&cpufreq_interface);
 err_null_driver:
         write_lock_irqsave(&cpufreq_driver_lock, flags);
-        rcu_assign_pointer(cpufreq_driver, NULL);
+        cpufreq_driver = NULL;
         write_unlock_irqrestore(&cpufreq_driver_lock, flags);
-        synchronize_rcu();
         return ret;
 }
 EXPORT_SYMBOL_GPL(cpufreq_register_driver);
@@ -2078,15 +1940,9 @@ EXPORT_SYMBOL_GPL(cpufreq_register_driver);
 int cpufreq_unregister_driver(struct cpufreq_driver *driver)
 {
         unsigned long flags;
-        struct cpufreq_driver *old_driver;
 
-        rcu_read_lock();
-        old_driver = rcu_access_pointer(cpufreq_driver);
-        if (!old_driver || (driver != old_driver)) {
-                rcu_read_unlock();
+        if (!cpufreq_driver || (driver != cpufreq_driver))
                 return -EINVAL;
-        }
-        rcu_read_unlock();
 
         pr_debug("unregistering driver %s\n", driver->name);
 
@@ -2094,9 +1950,8 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver)
         unregister_hotcpu_notifier(&cpufreq_cpu_notifier);
 
         write_lock_irqsave(&cpufreq_driver_lock, flags);
-        rcu_assign_pointer(cpufreq_driver, NULL);
+        cpufreq_driver = NULL;
         write_unlock_irqrestore(&cpufreq_driver_lock, flags);
-        synchronize_rcu();
 
         return 0;
 }