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

[Sumit Garg]

Hi Will,

On Tue, 26 Jan 2021 at 19:48, Will Deacon <will@xxxxxxxxxx> wrote:
>
> Hi Sumit,
>
> On Fri, Jan 15, 2021 at 05:31:41PM +0530, Sumit Garg 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@xxxxxxxxxx>
> > ---
>
> [...]
>
> > diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> > index 3605f77a..bafb7c8 100644
> > --- a/arch/arm64/kernel/perf_event.c
> > +++ b/arch/arm64/kernel/perf_event.c
> > @@ -23,6 +23,8 @@
> >  #include <linux/platform_device.h>
> >  #include <linux/sched_clock.h>
> >  #include <linux/smp.h>
> > +#include <linux/nmi.h>
> > +#include <linux/cpufreq.h>
> >
> >  /* ARMv8 Cortex-A53 specific event types. */
> >  #define ARMV8_A53_PERFCTR_PREF_LINEFILL                              0xC2
> > @@ -1246,12 +1248,30 @@ static struct platform_driver armv8_pmu_driver = {
> >       .probe          = armv8_pmu_device_probe,
> >  };
> >
> > +static int __init lockup_detector_init_fn(void *data)
> > +{
> > +     lockup_detector_init();
> > +     return 0;
> > +}
> > +
> >  static int __init armv8_pmu_driver_init(void)
> >  {
> > +     int ret;
> > +
> >       if (acpi_disabled)
> > -             return platform_driver_register(&armv8_pmu_driver);
> > +             ret = platform_driver_register(&armv8_pmu_driver);
> >       else
> > -             return arm_pmu_acpi_probe(armv8_pmuv3_init);
> > +             ret = arm_pmu_acpi_probe(armv8_pmuv3_init);
> > +
> > +     /*
> > +      * Try to re-initialize lockup detector after PMU init in
> > +      * case PMU events are triggered via NMIs.
> > +      */
> > +     if (ret == 0 && arm_pmu_irq_is_nmi())
> > +             smp_call_on_cpu(raw_smp_processor_id(), lockup_detector_init_fn,
> > +                             NULL, false);
> > +
> > +     return ret;
>
> What's wrong with the alternative approach outlined by Mark:
>
> https://lore.kernel.org/r/20210113130235.GB19011@C02TD0UTHF1T.local
>
> ?

I have replied on this thread.

-Sumit

>
> Will