linux-kernel - Re: [PATCH v2 5/8] perf auxtrace: Change to use SMP memory barriers

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Date:   Mon, 7 Jun 2021 13:02:50 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Leo Yan <leo.yan@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.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>,
        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 5/8] perf auxtrace: Change to use SMP memory barriers

On 2/06/21 1:30 pm, Leo Yan wrote:
> The kernel and the userspace tool can access the AUX ring buffer head
> and tail from different CPUs, thus SMP class of barriers are required
> on SMP system.
> 
> This patch changes to use SMP barriers to replace mb() and rmb()
> barriers.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>

Acked-by: Adrian Hunter <adrian.hunter@...el.com>

> ---
>  tools/perf/util/auxtrace.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
> index a4fbb33b7245..42b7ef811bde 100644
> --- a/tools/perf/util/auxtrace.h
> +++ b/tools/perf/util/auxtrace.h
> @@ -444,7 +444,7 @@ static inline u64 auxtrace_mmap__read_snapshot_head(struct auxtrace_mmap *mm)
>  	u64 head = READ_ONCE(pc->aux_head);
>  
>  	/* Ensure all reads are done after we read the head */
> -	rmb();
> +	smp_rmb();
>  	return head;
>  }
>  
> @@ -458,7 +458,7 @@ static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm)
>  #endif
>  
>  	/* Ensure all reads are done after we read the head */
> -	rmb();
> +	smp_rmb();
>  	return head;
>  }
>  
> @@ -470,7 +470,7 @@ static inline void auxtrace_mmap__write_tail(struct auxtrace_mmap *mm, u64 tail)
>  #endif
>  
>  	/* Ensure all reads are done before we write the tail out */
> -	mb();
> +	smp_mb();
>  #if BITS_PER_LONG == 64 || !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT)
>  	pc->aux_tail = tail;
>  #else
>