[PATCH] Rewrite lock in cpufreq to eliminate cpufreq/hotplug related issues
From: Venkatesh Pallipadi
Date: Fri Dec 29 2006 - 17:02:32 EST
Yet another attempt to resolve cpufreq and hotplug locking issues.
Patchset has 3 patches:
* Rewrite the lock infrastructure of cpufreq using a per cpu rwsem.
* Minor restructuring of work callback in ondemand driver.
* Use the new cpufreq rwsem infrastructure in ondemand work.
This patch:
Convert policy->lock to rwsem and move it to per_cpu area.
This rwsem will protect against both changing/accessing policy
related parameters and CPU hot plug/unplug.
Cc: Gautham R Shenoy <ego@xxxxxxxxxx>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
Index: linux-2.6.20-rc-mm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-2.6.20-rc-mm.orig/drivers/cpufreq/cpufreq.c
+++ linux-2.6.20-rc-mm/drivers/cpufreq/cpufreq.c
@@ -41,6 +41,64 @@ static struct cpufreq_driver *cpufreq_dr
static struct cpufreq_policy *cpufreq_cpu_data[NR_CPUS];
static DEFINE_SPINLOCK(cpufreq_driver_lock);
+/*
+ * cpu_policy_rwsem is a per CPU reader-writer semaphore designed to cure
+ * all cpufreq/hotplug/workqueue/etc related lock issues.
+ *
+ * The rules for this semaphore:
+ * - Any routine that wants to read from the policy structure will
+ * do a down_read on this semaphore.
+ * - Any routine that will write to the policy structure and/or may take away
+ * the policy altogether (eg. CPU hotplug), will hold this lock in write
+ * mode before doing so.
+ *
+ * Additional rules:
+ * - All holders of the lock should check to make sure that the CPU they
+ * are concerned with are online after they get the lock.
+ * - Governor routines that can be called in cpufreq hotplug path should not
+ * take this sem as top level hotplug notifier handler takes this.
+ */
+static DEFINE_PER_CPU(int, policy_cpu);
+static DEFINE_PER_CPU(struct rw_semaphore, cpu_policy_rwsem);
+
+#define lock_policy_rwsem(mode, cpu) \
+int lock_policy_rwsem_##mode \
+(int cpu) \
+{ \
+ int policy_cpu = per_cpu(policy_cpu, cpu); \
+ BUG_ON(policy_cpu == -1); \
+ down_##mode(&per_cpu(cpu_policy_rwsem, policy_cpu)); \
+ if (unlikely(!cpu_online(cpu))) { \
+ up_##mode(&per_cpu(cpu_policy_rwsem, policy_cpu)); \
+ return -1; \
+ } \
+ \
+ return 0; \
+}
+
+lock_policy_rwsem(read, cpu);
+EXPORT_SYMBOL_GPL(lock_policy_rwsem_read);
+
+lock_policy_rwsem(write, cpu);
+EXPORT_SYMBOL_GPL(lock_policy_rwsem_write);
+
+void unlock_policy_rwsem_read(int cpu)
+{
+ int policy_cpu = per_cpu(policy_cpu, cpu);
+ BUG_ON(policy_cpu == -1);
+ up_read(&per_cpu(cpu_policy_rwsem, policy_cpu));
+}
+EXPORT_SYMBOL_GPL(unlock_policy_rwsem_read);
+
+void unlock_policy_rwsem_write(int cpu)
+{
+ int policy_cpu = per_cpu(policy_cpu, cpu);
+ BUG_ON(policy_cpu == -1);
+ up_write(&per_cpu(cpu_policy_rwsem, policy_cpu));
+}
+EXPORT_SYMBOL_GPL(unlock_policy_rwsem_write);
+
+
/* internal prototypes */
static int __cpufreq_governor(struct cpufreq_policy *policy, unsigned int event);
static void handle_update(struct work_struct *work);
@@ -415,10 +473,8 @@ static ssize_t store_##file_name \
if (ret != 1) \
return -EINVAL; \
\
- mutex_lock(&policy->lock); \
ret = __cpufreq_set_policy(policy, &new_policy); \
policy->user_policy.object = policy->object; \
- mutex_unlock(&policy->lock); \
\
return ret ? ret : count; \
}
@@ -479,12 +535,10 @@ static ssize_t store_scaling_governor (s
/* Do not use cpufreq_set_policy here or the user_policy.max
will be wrongly overridden */
- mutex_lock(&policy->lock);
ret = __cpufreq_set_policy(policy, &new_policy);
policy->user_policy.policy = policy->policy;
policy->user_policy.governor = policy->governor;
- mutex_unlock(&policy->lock);
if (ret)
return ret;
@@ -589,11 +643,17 @@ static ssize_t show(struct kobject * kob
policy = cpufreq_cpu_get(policy->cpu);
if (!policy)
return -EINVAL;
+
+ if (lock_policy_rwsem_read(policy->cpu) < 0)
+ return -EINVAL;
+
if (fattr->show)
ret = fattr->show(policy, buf);
else
ret = -EIO;
+ unlock_policy_rwsem_read(policy->cpu);
+
cpufreq_cpu_put(policy);
return ret;
}
@@ -607,11 +667,17 @@ static ssize_t store(struct kobject * ko
policy = cpufreq_cpu_get(policy->cpu);
if (!policy)
return -EINVAL;
+
+ if (lock_policy_rwsem_write(policy->cpu) < 0)
+ return -EINVAL;
+
if (fattr->store)
ret = fattr->store(policy, buf, count);
else
ret = -EIO;
+ unlock_policy_rwsem_write(policy->cpu);
+
cpufreq_cpu_put(policy);
return ret;
}
@@ -685,8 +751,10 @@ static int cpufreq_add_dev (struct sys_d
policy->cpu = cpu;
policy->cpus = cpumask_of_cpu(cpu);
- mutex_init(&policy->lock);
- mutex_lock(&policy->lock);
+ /* Initially set CPU itself as the policy_cpu */
+ per_cpu(policy_cpu, cpu) = cpu;
+ lock_policy_rwsem_write(cpu);
+
init_completion(&policy->kobj_unregister);
INIT_WORK(&policy->update, handle_update);
@@ -696,7 +764,7 @@ static int cpufreq_add_dev (struct sys_d
ret = cpufreq_driver->init(policy);
if (ret) {
dprintk("initialization failed\n");
- mutex_unlock(&policy->lock);
+ unlock_policy_rwsem_write(cpu);
goto err_out;
}
@@ -710,6 +778,14 @@ static int cpufreq_add_dev (struct sys_d
*/
managed_policy = cpufreq_cpu_get(j);
if (unlikely(managed_policy)) {
+
+ /* Set proper policy_cpu */
+ unlock_policy_rwsem_write(cpu);
+ per_cpu(policy_cpu, cpu) = managed_policy->cpu;
+
+ if (lock_policy_rwsem_write(cpu) < 0)
+ goto err_out_driver_exit;
+
spin_lock_irqsave(&cpufreq_driver_lock, flags);
managed_policy->cpus = policy->cpus;
cpufreq_cpu_data[cpu] = managed_policy;
@@ -720,8 +796,8 @@ static int cpufreq_add_dev (struct sys_d
&managed_policy->kobj, "cpufreq");
cpufreq_debug_enable_ratelimit();
- mutex_unlock(&policy->lock);
ret = 0;
+ unlock_policy_rwsem_write(cpu);
goto err_out_driver_exit; /* call driver->exit() */
}
}
@@ -735,7 +811,7 @@ static int cpufreq_add_dev (struct sys_d
ret = kobject_register(&policy->kobj);
if (ret) {
- mutex_unlock(&policy->lock);
+ unlock_policy_rwsem_write(cpu);
goto err_out_driver_exit;
}
/* set up files for this cpu device */
@@ -750,8 +826,10 @@ static int cpufreq_add_dev (struct sys_d
sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
spin_lock_irqsave(&cpufreq_driver_lock, flags);
- for_each_cpu_mask(j, policy->cpus)
+ for_each_cpu_mask(j, policy->cpus) {
cpufreq_cpu_data[j] = policy;
+ per_cpu(policy_cpu, j) = policy->cpu;
+ }
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
/* symlink affected CPUs */
@@ -770,7 +848,7 @@ static int cpufreq_add_dev (struct sys_d
policy->governor = NULL; /* to assure that the starting sequence is
* run in cpufreq_set_policy */
- mutex_unlock(&policy->lock);
+ unlock_policy_rwsem_write(cpu);
/* set default policy */
ret = cpufreq_set_policy(&new_policy);
@@ -811,11 +889,13 @@ module_out:
/**
- * cpufreq_remove_dev - remove a CPU device
+ * __cpufreq_remove_dev - remove a CPU device
*
* Removes the cpufreq interface for a CPU device.
+ * Caller should already have policy_rwsem in write mode for this CPU.
+ * This routine frees the rwsem before returning.
*/
-static int cpufreq_remove_dev (struct sys_device * sys_dev)
+static int __cpufreq_remove_dev (struct sys_device * sys_dev)
{
unsigned int cpu = sys_dev->id;
unsigned long flags;
@@ -834,6 +914,7 @@ static int cpufreq_remove_dev (struct sy
if (!data) {
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
cpufreq_debug_enable_ratelimit();
+ unlock_policy_rwsem_write(cpu);
return -EINVAL;
}
cpufreq_cpu_data[cpu] = NULL;
@@ -850,6 +931,7 @@ static int cpufreq_remove_dev (struct sy
sysfs_remove_link(&sys_dev->kobj, "cpufreq");
cpufreq_cpu_put(data);
cpufreq_debug_enable_ratelimit();
+ unlock_policy_rwsem_write(cpu);
return 0;
}
#endif
@@ -858,6 +940,7 @@ static int cpufreq_remove_dev (struct sy
if (!kobject_get(&data->kobj)) {
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
cpufreq_debug_enable_ratelimit();
+ unlock_policy_rwsem_write(cpu);
return -EFAULT;
}
@@ -891,10 +974,10 @@ static int cpufreq_remove_dev (struct sy
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
#endif
- mutex_lock(&data->lock);
if (cpufreq_driver->target)
__cpufreq_governor(data, CPUFREQ_GOV_STOP);
- mutex_unlock(&data->lock);
+
+ unlock_policy_rwsem_write(cpu);
kobject_unregister(&data->kobj);
@@ -918,6 +1001,18 @@ static int cpufreq_remove_dev (struct sy
}
+static int cpufreq_remove_dev (struct sys_device * sys_dev)
+{
+ unsigned int cpu = sys_dev->id;
+ int retval;
+ if (unlikely(lock_policy_rwsem_write(cpu)))
+ BUG();
+
+ retval = __cpufreq_remove_dev(sys_dev);
+ return retval;
+}
+
+
static void handle_update(struct work_struct *work)
{
struct cpufreq_policy *policy =
@@ -965,9 +1060,12 @@ unsigned int cpufreq_quick_get(unsigned
unsigned int ret_freq = 0;
if (policy) {
- mutex_lock(&policy->lock);
+ if (unlikely(lock_policy_rwsem_read(cpu)))
+ return ret_freq;
+
ret_freq = policy->cur;
- mutex_unlock(&policy->lock);
+
+ unlock_policy_rwsem_read(cpu);
cpufreq_cpu_put(policy);
}
@@ -993,7 +1091,8 @@ unsigned int cpufreq_get(unsigned int cp
if (!cpufreq_driver->get)
goto out;
- mutex_lock(&policy->lock);
+ if (unlikely(lock_policy_rwsem_write(cpu)))
+ goto out;
ret_freq = cpufreq_driver->get(cpu);
@@ -1007,7 +1106,7 @@ unsigned int cpufreq_get(unsigned int cp
}
}
- mutex_unlock(&policy->lock);
+ unlock_policy_rwsem_write(cpu);
out:
cpufreq_cpu_put(policy);
@@ -1288,18 +1387,19 @@ int cpufreq_driver_target(struct cpufreq
if (!policy)
return -EINVAL;
- mutex_lock(&policy->lock);
+ if (unlikely(lock_policy_rwsem_write(policy->cpu)))
+ return -EINVAL;
ret = __cpufreq_driver_target(policy, target_freq, relation);
- mutex_unlock(&policy->lock);
+ unlock_policy_rwsem_write(policy->cpu);
cpufreq_cpu_put(policy);
return ret;
}
EXPORT_SYMBOL_GPL(cpufreq_driver_target);
-int cpufreq_driver_getavg(struct cpufreq_policy *policy)
+int __cpufreq_driver_getavg(struct cpufreq_policy *policy)
{
int ret = 0;
@@ -1307,17 +1407,13 @@ int cpufreq_driver_getavg(struct cpufreq
if (!policy)
return -EINVAL;
- mutex_lock(&policy->lock);
-
if (cpu_online(policy->cpu) && cpufreq_driver->getavg)
ret = cpufreq_driver->getavg(policy->cpu);
- mutex_unlock(&policy->lock);
-
cpufreq_cpu_put(policy);
return ret;
}
-EXPORT_SYMBOL_GPL(cpufreq_driver_getavg);
+EXPORT_SYMBOL_GPL(__cpufreq_driver_getavg);
/*
* when "event" is CPUFREQ_GOV_LIMITS
@@ -1401,9 +1497,7 @@ int cpufreq_get_policy(struct cpufreq_po
if (!cpu_policy)
return -EINVAL;
- mutex_lock(&cpu_policy->lock);
memcpy(policy, cpu_policy, sizeof(struct cpufreq_policy));
- mutex_unlock(&cpu_policy->lock);
cpufreq_cpu_put(cpu_policy);
return 0;
@@ -1519,8 +1613,9 @@ int cpufreq_set_policy(struct cpufreq_po
if (!data)
return -EINVAL;
- /* lock this CPU */
- mutex_lock(&data->lock);
+ if (unlikely(lock_policy_rwsem_write(policy->cpu)))
+ return -EINVAL;
+
ret = __cpufreq_set_policy(data, policy);
data->user_policy.min = data->min;
@@ -1528,7 +1623,7 @@ int cpufreq_set_policy(struct cpufreq_po
data->user_policy.policy = data->policy;
data->user_policy.governor = data->governor;
- mutex_unlock(&data->lock);
+ unlock_policy_rwsem_write(policy->cpu);
cpufreq_cpu_put(data);
@@ -1553,7 +1648,8 @@ int cpufreq_update_policy(unsigned int c
if (!data)
return -ENODEV;
- mutex_lock(&data->lock);
+ if (unlikely(lock_policy_rwsem_write(cpu)))
+ return -EINVAL;
dprintk("updating policy for CPU %u\n", cpu);
memcpy(&policy, data, sizeof(struct cpufreq_policy));
@@ -1578,7 +1674,8 @@ int cpufreq_update_policy(unsigned int c
ret = __cpufreq_set_policy(data, &policy);
- mutex_unlock(&data->lock);
+ unlock_policy_rwsem_write(cpu);
+
cpufreq_cpu_put(data);
return ret;
}
@@ -1588,31 +1685,28 @@ static int cpufreq_cpu_callback(struct n
unsigned long action, void *hcpu)
{
unsigned int cpu = (unsigned long)hcpu;
- struct cpufreq_policy *policy;
struct sys_device *sys_dev;
+ struct cpufreq_policy *policy;
sys_dev = get_cpu_sysdev(cpu);
-
if (sys_dev) {
switch (action) {
case CPU_ONLINE:
cpufreq_add_dev(sys_dev);
break;
case CPU_DOWN_PREPARE:
- /*
- * We attempt to put this cpu in lowest frequency
- * possible before going down. This will permit
- * hardware-managed P-State to switch other related
- * threads to min or higher speeds if possible.
- */
+ if (unlikely(lock_policy_rwsem_write(cpu)))
+ BUG();
+
policy = cpufreq_cpu_data[cpu];
if (policy) {
- cpufreq_driver_target(policy, policy->min,
+ __cpufreq_driver_target(policy, policy->min,
CPUFREQ_RELATION_H);
}
+ __cpufreq_remove_dev(sys_dev);
break;
- case CPU_DEAD:
- cpufreq_remove_dev(sys_dev);
+ case CPU_DOWN_FAILED:
+ cpufreq_add_dev(sys_dev);
break;
}
}
@@ -1726,3 +1820,16 @@ int cpufreq_unregister_driver(struct cpu
return 0;
}
EXPORT_SYMBOL_GPL(cpufreq_unregister_driver);
+
+static int __init cpufreq_core_init(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu) {
+ per_cpu(policy_cpu, cpu) = -1;
+ init_rwsem(&per_cpu(cpu_policy_rwsem, cpu));
+ }
+ return 0;
+}
+
+core_initcall(cpufreq_core_init);
Index: linux-2.6.20-rc-mm/include/linux/cpufreq.h
===================================================================
--- linux-2.6.20-rc-mm.orig/include/linux/cpufreq.h
+++ linux-2.6.20-rc-mm/include/linux/cpufreq.h
@@ -84,9 +84,6 @@ struct cpufreq_policy {
unsigned int policy; /* see above */
struct cpufreq_governor *governor; /* see below */
- struct mutex lock; /* CPU ->setpolicy or ->target may
- only be called once a time */
-
struct work_struct update; /* if update_policy() needs to be
* called, but you're in IRQ context */
@@ -172,11 +169,16 @@ extern int __cpufreq_driver_target(struc
unsigned int relation);
-extern int cpufreq_driver_getavg(struct cpufreq_policy *policy);
+extern int __cpufreq_driver_getavg(struct cpufreq_policy *policy);
int cpufreq_register_governor(struct cpufreq_governor *governor);
void cpufreq_unregister_governor(struct cpufreq_governor *governor);
+int lock_policy_rwsem_read(int cpu);
+int lock_policy_rwsem_write(int cpu);
+void unlock_policy_rwsem_read(int cpu);
+void unlock_policy_rwsem_write(int cpu);
+
/*********************************************************************
* CPUFREQ DRIVER INTERFACE *
-
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