linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Fix for HWP interrupt before driver is ready

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Date:   Tue, 7 Sep 2021 15:41:23 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: Fix for HWP interrupt before
 driver is ready

On Mon, Sep 6, 2021 at 9:57 PM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> On Mon, 2021-09-06 at 20:25 +0200, Rafael J. Wysocki wrote:
> > On Mon, Sep 6, 2021 at 8:14 PM Srinivas Pandruvada
> > <srinivas.pandruvada@...ux.intel.com> wrote:
> > >
> > > On Mon, 2021-09-06 at 19:54 +0200, Rafael J. Wysocki wrote:
> > > >
> [...]
>
> > > >
> > > We are handling offline for other thermal interrupt sources from
> > > same
> > > interrupt in therm-throt.c, where we do similar in offline path (by
> > > TGLX). If cpufreq offline can cause such issue of changing CPU,
> >
> > This is not cpufreq offline, but intel_pstate_update_status() which
> > may be triggered via sysfs.  And again, the theoretically problematic
> > thing is dereferencing cpudata (which may be cleared by a remote CPU)
> > from the interrupt handler without protection.
>
> This will be a problem.
>
> >
> > > I can call intel_pstate_disable_hwp_interrupt() via override from
> > > https://elixir.bootlin.com/linux/latest/C/ident/thermal_throttle_offline
> > > after masking APIC interrupt.
> >
> > But why would using RCU be harder than this?
> I think, this will require all_cpu_data and cpu_data to be rcu
> protected. This needs to be well tested.
>
> I think better to revert the patch for the next release.

Done, thanks!