linux-kernel - Re: [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in __cpufreq

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Date:	Tue, 2 Feb 2016 12:04:49 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Juri Lelli <juri.lelli@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Turquette <mturquette@...libre.com>,
	Steve Muckle <steve.muckle@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	dietmar.eggemann@....com
Subject: Re: [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in
 __cpufreq_governor

On 01-02-16, 12:24, Saravana Kannan wrote:
> On 02/01/2016 02:22 AM, Rafael J. Wysocki wrote:
> I'm not sure whose idea you are referring to. Viresh's (I don't think I saw
> his proposal) or mine.

http://git.linaro.org/people/viresh.kumar/linux.git/commit/57714d5b1778f2f610bcc5c74d85b29ba1cc1995

> Anyway, to explain my suggestion better, I'm proposing to make it so that we
> don't have a need for the AB BA locking. The only reason the governor needs
> to even grab the sysfs lock is to add/remove the sysfs attribute files.
> 
> That can be easily achieved if the policy struct has some "gov_attrs"
> field(s) that each governor populates. Then the framework just has to create
> them after POLICY_INIT is processed by the governor and remove them before
> POILICY_EXIT is sent to the governor.

What will that solve? It will stay exactly same then as well, as we
would be adding/removing these attributes from within the same
policy->rwsem ..

> That way, we also avoid having to worry about the gov attributes accessed by
> the show/store disappearing while the files are being accessed.

It can't happen. S_active lock should be taking care of that, isn't
it?

-- 
viresh