linux-kernel - Re: [PATCH v2 2/10] cpufreq: governor: Use common mutex for dbs

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Message-ID: <2182507.NaCeYsVQeB@vostro.rjw.lan>
Date:	Sun, 07 Feb 2016 15:33:07 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	Saravana Kannan <skannan@...eaurora.org>
Subject: Re: [PATCH v2 2/10] cpufreq: governor: Use common mutex for dbs_data protection

On Sunday, February 07, 2016 03:01:12 PM Viresh Kumar wrote:
> On 05-02-16, 23:59, Rafael J. Wysocki wrote:
> > One more observation here.
> > 
> > If we are able to eliminate dbs_data_mutex from update_sampling_rate(),
> > then cpufreq_governor_dbs() becomes the only user of that lock.  Further,
> > if we can guarantee that the governor's ->governor callback will always
> > be invoked under policy->rwsem, dbs_data_mutex becomes unnecessary and
> > may be dropped.
> 
> That will be guaranteed with my 7 patches, which I will rebase and send again.
> 
> But there are cases where a single dbs_data is going to be used for multiple
> policies and so relying on policy->rwsem isn't going to be sufficient.
> 
> But, yeah, we should be able to narrow down the locked area I believe.

That should only be a matter of protecting the gov->gdbs_data object and its
refcount then.

Thanks,
Rafael