linux-kernel - Re: [PATCH 0/5] cpufreq: Fixes for 3.12

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Date:	Tue, 20 Aug 2013 14:43:42 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] cpufreq: Fixes for 3.12

On Tuesday, August 20, 2013 12:08:21 PM Viresh Kumar wrote:
> Hi Rafael,
> 
> You recently did this:
> 
> commit 878f6e074e9a7784a6e351512eace4ccb3542eef
> Author: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Date:   Sun Aug 18 15:35:59 2013 +0200
> 
>     Revert "cpufreq: Use cpufreq_policy_list for iterating over policies"
>     
>     Revert commit eb60852 (cpufreq: Use cpufreq_policy_list for iterating
>     over policies), because it breaks system suspend/resume on multiple
>     machines.
>     
>     It either causes resume to block indefinitely or causes the BUG_ON()
>     in lock_policy_rwsem_##mode() to trigger on sysfs accesses to cpufreq
>     attributes.
>     
> ------x------------x---------------
> 
> This patchset gets the reverted patch back along with few supporting patches.
> Cause of the initial problem you observed was this:
> 
> - At suspend all CPUs are removed leaving boot cpu. At this time policies aren't
>   freed and also aren't removed from cpufreq_policy_list. And per-cpu variable
>   cpufreq_cpu_data is marked as NULL.
> - At resume CPUs other than boot cpu called __cpufreq_add_dev(). The tricky
>   change that was introduced by my patch was: We iterate over list of policies
>   instead of CPUs, where we used to get policy structure associated with
>   CPUs using per-cpu variable. Which used to be NULL for first CPU of a policy
>   that turned up. For the first cpu we don't want to call
>   cpufreq_add_policy_cpu() but want __cpufreq_add_add() to continue.
> 
>   When we called cpufreq_add_policy_cpu() it tried to stop the governor (which
>   was already stopped) and hence errors leading into unstable state.
> 
> This patchset fixes these issues and is tested with suspend-resume over my
> thinkpad with ubuntu. Apart from minor cleanups it removes policy from
> cpufreq_policy_list in case of suspend/resume as well and hence we will never
> call cpufreq_add_policy_cpu() for first cpu of a policy.

Well, this looks good, but do we really need it in 3.12?  It doesn't look
like 3.12 will be missing these changes a lot?

Rafael

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