linux-kernel - Re: [Eas-dev] [PATCH V4 1/3] sched: cpufreq: Allow remote cpufreq callbacks

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Date:   Thu, 27 Jul 2017 11:20:26 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Joel Fernandes (Google)" <joel.opensrc@...il.com>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-pm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        smuckle.linux@...il.com, eas-dev@...ts.linaro.org,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [Eas-dev] [PATCH V4 1/3] sched: cpufreq: Allow remote cpufreq
 callbacks

On 26-07-17, 22:34, Joel Fernandes (Google) wrote:
> On Wed, Jul 26, 2017 at 2:22 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > @@ -221,7 +226,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
> >         sugov_set_iowait_boost(sg_cpu, time, flags);
> >         sg_cpu->last_update = time;
> >
> > -       if (!sugov_should_update_freq(sg_policy, time))
> > +       if (!sugov_should_update_freq(sg_policy, time, hook->cpu))
> >                 return;
> 
> Since with the remote callbacks now possible, isn't it unsafe to
> modify sg_cpu and sg_policy structures without a lock in
> sugov_update_single?
> 
> Unlike sugov_update_shared, we don't acquire any lock in
> sugov_update_single before updating these structures. Did I miss
> something?

As Peter already mentioned it earlier, the callbacks are called with
rq locks held and so sugov_update_single() wouldn't get called in
parallel for a target CPU.

That's the only race you were worried about ?

-- 
viresh