linux-kernel - Re: [PATCH V5 01/12] perf/core: Add aux_pause, aux_resume, aux_start

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Message-ID: <ZcVuK1nnxG18ps-a@tassilo>
Date: Thu, 8 Feb 2024 16:13:31 -0800
From: Andi Kleen <ak@...ux.intel.com>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Thomas Richter <tmricht@...ux.ibm.com>,
	Hendrik Brueckner <brueckner@...ux.ibm.com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	James Clark <james.clark@....com>, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org,
	Yicong Yang <yangyicong@...ilicon.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Will Deacon <will@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH V5 01/12] perf/core: Add aux_pause, aux_resume,
 aux_start_paused

> +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