linux-kernel - Re: [PATCH V4 1/7] cpufreq: Merge cpufreq_offline

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Date:	Thu, 11 Feb 2016 01:59:24 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Rafael Wysocki <rjw@...ysocki.net>,
	Juri Lelli <juri.lelli@....com>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4 1/7] cpufreq: Merge cpufreq_offline_prepare/finish routines

On Tue, Feb 9, 2016 at 4:46 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> The offline routine was separated into two halves earlier by
> 'commit 1aee40ac9c86 ("cpufreq: Invoke __cpufreq_remove_dev_finish()
> after releasing cpu_hotplug.lock");.
>
> And the reasons cited were, race issues between accessing policy's sysfs
> files and policy kobject's cleanup.
>
> That race isn't valid anymore, as we don't remove the policy & its
> kobject completely on hotplugs, but do that from ->remove() callback of
> subsys framework.

Governor sysfs attributes are still removed in
__cpufreq_governor(_EXIT), though, so had store() been used for them,
the deadlock described in the changelog of commit 1aee40ac9c86 would
have been possible.

Fortunately, we don't use store() (which still does get_online_cpus())
for those attributes now.  We use governor_store() for them and that
doesn't call get_online_cpus().  So in fact this patch is only correct
after the recent rework of the governor attributes handling.

Please modify the changelog to explain that more thoroughly.

Thanks,
Rafael