Re: [PATCH v4 6/9] arm64: perf: Do not call irq_work_run in NMI context

[Will Deacon <will@kernel.org>]

On Wed, Jul 17, 2019 at 09:17:09AM +0100, Julien Thierry wrote:
> Function irq_work_run is not NMI safe and should not be called from NMI
> context.
> 
> When PMU interrupt is an NMI do not call irq_work_run. Instead rely on the
> IRQ work IPI to run the irq_work queue once NMI/IRQ contexts have been
> exited.
> 
> Signed-off-by: Julien Thierry <julien.thierry@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Jiri Olsa <jolsa@redhat.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> ---
>  arch/arm64/kernel/perf_event.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index 0e2cf5d..9c959ad 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -776,20 +776,16 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
>  		if (!armpmu_event_set_period(event))
>  			continue;
>  
> +		/*
> +		 * Perf event overflow will queue the processing of the event as
> +		 * an irq_work which will be taken care of in the handling of
> +		 * IPI_IRQ_WORK.
> +		 */
>  		if (perf_event_overflow(event, &data, regs))
>  			cpu_pmu->disable(event);
>  	}
>  	armv8pmu_start(cpu_pmu);
>  
> -	/*
> -	 * Handle the pending perf events.
> -	 *
> -	 * Note: this call *must* be run with interrupts disabled. For
> -	 * platforms that can have the PMU interrupts raised as an NMI, this
> -	 * will not work.
> -	 */
> -	irq_work_run();

What about the case where NMIs are not being used (e.g. GICv2)?

Will

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