linux-kernel - Re: [PATCH 1/2] cpufreq: qcom-hw: Use initialized cpumask for thermal pressure update

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Date:   Wed, 19 Jan 2022 12:10:29 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Lukasz Luba <lukasz.luba@....com>,
        Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Thara Gopinath <thara.gopinath@...il.com>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH 1/2] cpufreq: qcom-hw: Use initialized cpumask for
 thermal pressure update

On 19-01-22, 12:05, Viresh Kumar wrote:
> policy->cpus keeps on changing with CPU hotplug and this can leave
> your platform in an inconsistent state. For example, in case where you
> offline a CPU from policy, other CPUs get their thermal pressure
> updated, online the CPU back and all CPUs of a policy don't have the
> same settings anymore.
> 
> There are few things we can do here now:
> 
> - Check for empty related_cpus and return early. Since related_cpus is
>   updated only once, this shall work just fine and must not be racy.
> 
>   While at it, I think we can also do something like this in
>   topology_update_thermal_pressure() instead:
> 
>   	cpu = cpumask_first(cpus);
>         if (unlikely(cpu >= NR_CPUS))
>                 return;
> 
> - And while writing this email, I dropped all other ideas in favor of
>   change to topology_update_thermal_pressure() :)

And then I saw your second patch, which looks good as otherwise we
will not be able to catch the bug in our system where we are sending
the empty cpumask :)

So the other idea is:

- Revert, or bring back a new version of this and register the
  interrupt from there. But that is also not a very clean solution.

  commit 4bf8e582119e ("cpufreq: Remove ready() callback")

- 

-- 
viresh