On 09/17/2013 09:20 PM, Viresh Kumar wrote:
> We have per-cpu cpu_policy_rwsem for cpufreq core, but we never use all of them.
> We always use rwsem of policy->cpu and so we can actually make this rwsem per
> policy instead.
>
> This patch does this change. With this change other tricky situations are also
> avoided now, like which lock to take while we are changing policy->cpu, etc.
>
> Suggested-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
> Can be taken for 3.13.. Tested on my thinkpad with basic suspend/resume and
> hotplug tests.
>
> Was rebased on pm/linux-next with following additional patches:
> cpufreq: unlock correct rwsem while updating policy->cpu
> cpufreq: make return type of lock_policy_rwsem_{read|write}() as void
>
The code looks good, but the patch doesn't apply properly, because of the code
change that went in in your patch "cpufreq: Clear policy->cpus bits in
__cpufreq_remove_dev_finish()".
> @@ -1193,12 +1147,12 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
> policy->governor->name, CPUFREQ_NAME_LEN);
> #endif
>
> - lock_policy_rwsem_write(cpu);
> + down_write(&policy->rwsem);
> cpus = cpumask_weight(policy->cpus);
>
> if (cpus > 1)
> cpumask_clear_cpu(cpu, policy->cpus);
> - unlock_policy_rwsem_write(cpu);
> + up_write(&policy->rwsem);
>
> if (cpu != policy->cpu) {
> if (!frozen)
> @@ -1239,9 +1193,9 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
> return -EINVAL;
> }
>
> - lock_policy_rwsem_read(cpu);
> + down_read(&policy->rwsem);
> cpus = cpumask_weight(policy->cpus);
> - unlock_policy_rwsem_read(cpu);
> + up_read(&policy->rwsem);
>
The cpumask_clear_cpu() has been moved to _dev_finish() in Rafael's linux-next
tree. Hence the trouble. So kindly rework this patch on top of that.
> /* If cpu is last user of policy, free policy */
> if (cpus == 1) {
[...]
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index fcabc42..03735e7 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -85,6 +85,22 @@ struct cpufreq_policy {
> struct list_head policy_list;
> struct kobject kobj;
> struct completion kobj_unregister;
> +
> + /*
> + * 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:
> + * - Governor routines that can be called in cpufreq hotplug path should not
> + * take this sem as top level hotplug notifier handler takes this.
I think this comment is obsolete. I don't see the top-level hotplug notifier handler
(cpufreq_cpu_callback) acquiring the rwsem. Good to fix this comment while we are
at it, perhaps in a separate patch. (The comment above __cpufreq_remove_dev about
the policy-rwsem appears to be similarly out of date).
> + * - Lock should not be held across
> + * __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT);
> + */
> + struct rw_semaphore rwsem;
> };
>
> /* Only for ACPI */
>
Regards,
Srivatsa S. Bhat
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