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

[Will Deacon]

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

?

Will