linux-kernel - Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

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Message-ID: <20210419170331.GB31045@willie-the-truck>
Date:   Mon, 19 Apr 2021 18:03:32 +0100
From:   Will Deacon <will@...nel.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     Alexandru Elisei <alexandru.elisei@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Lecopzer Chen <lecopzer@...il.com>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Stephen Boyd <swboyd@...omium.org>, yj.chiang@...iatek.com
Subject: Re: [PATCH v5] arm64: Enable perf events based hard lockup detector

On Mon, Apr 12, 2021 at 05:31:13PM +0530, Sumit Garg wrote:
> On Tue, 30 Mar 2021 at 18:00, Sumit Garg <sumit.garg@...aro.org> wrote:
> > On Tue, 30 Mar 2021 at 14:07, Lecopzer Chen <lecopzer.chen@...iatek.com> wrote:
> > > > > On Fri, 15 Jan 2021 at 17:32, Sumit Garg <sumit.garg@...aro.org> wrote:
> > > > > >
> > > > > > With the recent feature added to enable perf events to use pseudo NMIs
> > > > > > as interrupts on platforms which support GICv3 or later, its now been
> > > > > > possible to enable hard lockup detector (or NMI watchdog) on arm64
> > > > > > platforms. So enable corresponding support.
> > > > > >
> > > > > > One thing to note here is that normally lockup detector is initialized
> > > > > > just after the early initcalls but PMU on arm64 comes up much later as
> > > > > > device_initcall(). So we need to re-initialize lockup detection once
> > > > > > PMU has been initialized.
> > > > > >
> > > > > > Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> > > > > > ---
> > > > > >
> > > > > > Changes in v5:
> > > > > > - Fix lockup_detector_init() invocation to be rather invoked from CPU
> > > > > >   binded context as it makes heavy use of per-cpu variables and shouldn't
> > > > > >   be invoked from preemptible context.
> > > > > >
> > > > >
> > > > > Do you have any further comments on this?
> > > > >
> 
> Since there aren't any further comments, can you re-pick this feature for 5.13?

I'd still like Mark's Ack on this, as the approach you have taken doesn't
really sit with what he was suggesting.

I also don't understand how all the CPUs get initialised with your patch,
since the PMU driver will be initialised after SMP is up and running.

Will