linux-kernel - Re: [PATCH v2 7/8] perf auxtrace: Use WRITE_ONCE() for updating aux

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Message-ID: <YL47tdD0ygaErZu+@hirez.programming.kicks-ass.net>
Date:   Mon, 7 Jun 2021 17:31:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 7/8] perf auxtrace: Use WRITE_ONCE() for updating
 aux_tail

On Wed, Jun 02, 2021 at 06:30:06PM +0800, Leo Yan wrote:
> Use WRITE_ONCE() for updating aux_tail, so can avoid unexpected memory
> behaviour.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> ---
>  tools/perf/util/auxtrace.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
> index e625bc76cdde..abc4282f5272 100644
> --- a/tools/perf/util/auxtrace.h
> +++ b/tools/perf/util/auxtrace.h
> @@ -458,7 +458,7 @@ static inline void auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail)
>  
>  	/* Ensure all reads are done before we write the tail out */
>  	smp_mb();
> -	pc->aux_tail = tail;
> +	WRITE_ONCE(pc->aux_tail, tail);
>  }
>  
>  int auxtrace_mmap__mmap(struct auxtrace_mmap *mm,
> -- 
> 2.25.1
>