linux-kernel - Re: [PATCH] cpufreq: Set policy to non-NULL only after all hotplug online work is done

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Message-ID: <530E4C8A.6060906@codeaurora.org>
Date:	Wed, 26 Feb 2014 12:20:26 -0800
From:	Saravana Kannan <skannan@...eaurora.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arm-msm@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] cpufreq: Set policy to non-NULL only after all hotplug
 online work is done

On 02/25/2014 10:02 PM, Viresh Kumar wrote:
> On 26 February 2014 07:18, Saravana Kannan <skannan@...eaurora.org> wrote:
>> On 02/25/2014 02:41 PM, Rafael J. Wysocki wrote:
>
>>> And is "fully initialized" actually well defined?
>>
>> The point in add dev/hot plug path after which we will no longer change
>> policy fields without sending further CPUFREQ_UPDATE_POLICY_CPU /
>> CPUFRE_NOTIFY notifiers.
>
> Okay..
>
>> Pretty much the end of __cpufreq_add_dev() so that it's after:
>> - cpufreq_init_policy()
>> - And the update of userpolicy fields that after thie init call
>
> No. In that case it can be considered initialized before cpufreq_init_policy().
> As we do send CPUFREQ_NOTIFY after that from cpufreq_init_policy()->
> cpufreq_set_policy().

Ok, valid hole in my definition of "fully initialized".
>
> There are two types of fields within policy, some are very basic: cpu/min/max/
> affected_cpus/related_cpus
>
> some are advanced: sysfs/governors/..
>
> And as a rule you have to get policy->rwsem lock before accessing policy
> members. We might not have followed it very well for small things like cpu.
>
> And so if you are doing anything over that, please use a lock and that is
> already present in cpufreq_update_policy().
>
> With my latest patchset that I sent yesterday, locking is improved and now
> a policy will be usable only after the rwsem is released. And that should be
> fine. And so making it available in the per-cpu variable after all the necessary
> fields are filled looks fine to me. And so I don't think we need to move it
> after call to cpufreq_init_policy(maybe a better name to this function is
> required)..

I'll take a closer look. Internal tree cpufreq code is in 3.12, so 
back-porting all the cpufreq changes and testing it can take a bit of 
time. Will get back on this.

-Saravana


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