Re: [PATCH V5 01/12] perf/core: Add aux_pause, aux_resume, aux_start_paused

[Andi Kleen <ak@linux.intel.com>]

> +static void __perf_event_aux_pause(struct perf_event *event, bool pause)
> +{
> +	if (pause) {
> +		if (!READ_ONCE(event->aux_paused)) {
> +			WRITE_ONCE(event->aux_paused, 1);
> +			event->pmu->stop(event, PERF_EF_PAUSE);
> +		}
> +	} else {
> +		if (READ_ONCE(event->aux_paused)) {
> +			WRITE_ONCE(event->aux_paused, 0);
> +			event->pmu->start(event, PERF_EF_RESUME);
> +		}

This doesn't look atomic. Either the READ/WRITE once are not needed,
or you need an actually atomic construct.

> +
> +	rb = ring_buffer_get(event);
> +	if (!rb)
> +		return;
> +
> +	local_irq_save(flags);
> +	/* Guard against NMI, NMI loses here */
> +	if (READ_ONCE(rb->aux_in_pause_resume))
> +		goto out_restore;
> +	WRITE_ONCE(rb->aux_in_pause_resume, 1);


> +	barrier();
> +	__perf_event_aux_pause(event, pause);
> +	barrier();
> +	WRITE_ONCE(rb->aux_in_pause_resume, 0);

Dito.

-Andi