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