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

Bjorn Andersson
2022-01-19T15:05:37Z

On Tue 18 Jan 22:40 PST 2022, Viresh Kumar wrote:

> 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.
> >

Oh, I didn't know that. Then my proposal doesn't seem that awesome.

> > 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")
>

We could do this and keep the interrupt disabled until we hit ready().

But I found the resulting issue non-trivial to debug, so I would prefer
if arch_update_thermal_pressure() dealt with the empty cpumask. So as
you suggest in your first reply, I'll respin the second patch alone,
without the WARN_ON().

Thanks,
Bjorn