linux-kernel - Re: [PATCH v2 2/2] cpufreq: qcom-hw: Delay enabling throttle

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Message-ID: <20220209073848.os3i7unf2qw3un3i@vireshk-i7>
Date:   Wed, 9 Feb 2022 13:08:48 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Lukasz Luba <lukasz.luba@....com>,
        Jonathan Corbet <corbet@....net>, linux-pm@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 2/2] cpufreq: qcom-hw: Delay enabling throttle_irq

On 28-01-22, 10:30, Bjorn Andersson wrote:
> On Fri 28 Jan 02:39 PST 2022, Lukasz Luba wrote:
> > On 1/28/22 3:25 AM, Bjorn Andersson wrote:
> > > In the event that the SoC is under thermal pressure while booting it's
> > > possible for the dcvs notification to happen inbetween the cpufreq
> > > framework calling init and it actually updating the policy's
> > > related_cpus cpumask.
> > > 
> > > Prior to the introduction of the thermal pressure update helper an empty
> > > cpumask would simply result in the thermal pressure of no cpus being
> > > updated, but the new code will attempt to dereference an invalid per_cpu
> > > variable.
> > 
> > Just to confirm, is that per-cpu var the 'policy->related_cpus' in this
> > driver?
> > 
> 
> Correct, we boot under thermal pressure, so the interrupt fires before
> we return from "init", which means that related_cpus is still 0.

Just to clarify here a bit, policy->related_cpus is already allocated at this
point of time. AFAICT, the dereferencing of the invalid per-cpu variable refers
to the per-cpu freq_factor in arch_topology.c, which happens because the cpumask
isn't initialized yet.

-- 
viresh