Messages in this thread | | | Date | Thu, 16 May 2013 14:14:13 +0800 | From | Xiaoguang Chen <> | Subject | Re: [PATCH] cpufreq: fix governor start/stop race condition |
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On 05/13/2013 06:47 PM, Xiaoguang Chen wrote: > cpufreq governor stop and start should be kept in sequence. > If not, there will be unexpected behavior, for example: > > we have 4 cpus and policy->cpu=cpu0, cpu1/2/3 are linked to cpu0. > the normal sequence is as below: > > 1) Current governor is userspace, one application tries to set > governor to ondemand. it will call __cpufreq_set_policy in which it > will stop userspace governor and then start ondemand governor. > > 2) Current governor is userspace, now cpu0 hotplugs in cpu3, it will > call cpufreq_add_policy_cpu. on which it first stops userspace > governor, and then starts userspace governor. > > Now if the sequence of above two cases interleaves, it becames > below sequence: > > 1) application stops userspace governor > 2) hotplug stops userspace governor > 3) application starts ondemand governor > 4) hotplug starts a governor > > in step 4, hotplug is supposed to start userspace governor, but now > the governor has been changed by application to ondemand, so hotplug > starts ondemand governor again !!!! > > The solution is as below: > cpufreq policy has a rwsem to protect the read and write of policy. > make the scope of the rwsem to contain cpufreq governor stop/start > sequence, so that after the stop governor has started, other threads > will not stop governor, they have to wait the current thread starts > the governor and then do their job. > > Change-Id: I054bb52789fc8abdcf80bdcc1caebd429c182bb0 > Signed-off-by: Xiaoguang Chen <chenxg@marvell.com> > --- > drivers/cpufreq/cpufreq.c | 19 ++++++++----------- > 1 file changed, 8 insertions(+), 11 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 1b8a48e..935f750 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -811,14 +811,14 @@ static int cpufreq_add_policy_cpu(unsigned int cpu, unsigned int sibling, > int ret = 0, has_target = !!cpufreq_driver->target; > unsigned long flags; > > + lock_policy_rwsem_write(sibling); > + > policy = cpufreq_cpu_get(sibling); > WARN_ON(!policy); > > if (has_target) > __cpufreq_governor(policy, CPUFREQ_GOV_STOP); > > - lock_policy_rwsem_write(sibling); > - > write_lock_irqsave(&cpufreq_driver_lock, flags); > > cpumask_set_cpu(cpu, policy->cpus); > @@ -826,13 +826,13 @@ static int cpufreq_add_policy_cpu(unsigned int cpu, unsigned int sibling, > per_cpu(cpufreq_cpu_data, cpu) = policy; > write_unlock_irqrestore(&cpufreq_driver_lock, flags); > > - unlock_policy_rwsem_write(sibling); > - > if (has_target) { > __cpufreq_governor(policy, CPUFREQ_GOV_START); > __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS); > } > > + unlock_policy_rwsem_write(sibling); > + > ret = sysfs_create_link(&dev->kobj, &policy->kobj, "cpufreq"); > if (ret) { > cpufreq_cpu_put(policy); > @@ -1028,6 +1028,8 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif > return -EINVAL; > } > > + WARN_ON(lock_policy_rwsem_write(cpu)); > + > if (cpufreq_driver->target) > __cpufreq_governor(data, CPUFREQ_GOV_STOP); > > @@ -1037,12 +1039,10 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif > data->governor->name, CPUFREQ_NAME_LEN); > #endif > > - WARN_ON(lock_policy_rwsem_write(cpu)); > cpus = cpumask_weight(data->cpus); > > if (cpus > 1) > cpumask_clear_cpu(cpu, data->cpus); > - unlock_policy_rwsem_write(cpu); > > if (cpu != data->cpu) { > sysfs_remove_link(&dev->kobj, "cpufreq"); > @@ -1054,7 +1054,6 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif > if (ret) { > pr_err("%s: Failed to move kobj: %d", __func__, ret); > > - WARN_ON(lock_policy_rwsem_write(cpu)); > cpumask_set_cpu(cpu, data->cpus); > > write_lock_irqsave(&cpufreq_driver_lock, flags); > @@ -1068,9 +1067,7 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif > return -EINVAL; > } > > - WARN_ON(lock_policy_rwsem_write(cpu)); > update_policy_cpu(data, cpu_dev->id); > - unlock_policy_rwsem_write(cpu); > pr_debug("%s: policy Kobject moved to cpu: %d from: %d\n", > __func__, cpu_dev->id, cpu); > } > @@ -1083,10 +1080,8 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif > if (cpufreq_driver->target) > __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT); > > - lock_policy_rwsem_read(cpu); > kobj = &data->kobj; > cmp = &data->kobj_unregister; > - unlock_policy_rwsem_read(cpu); > kobject_put(kobj); > > /* we need to make sure that the underlying kobj is actually > @@ -1108,6 +1103,8 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif > __cpufreq_governor(data, CPUFREQ_GOV_LIMITS); > } > > + unlock_policy_rwsem_write(cpu); > + > per_cpu(cpufreq_policy_cpu, cpu) = -1; > return 0; > } Hi, Guys What's your opinion about this patch?
-- Thanks Xiaoguang
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