linux-kernel - Re: [PATCH v5 2/9] coresight: tmc-etr: Add barrier after updating AUX ring buffer

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Message-ID: <20210829105500.GB14461@leoy-ThinkPad-X240s>
Date:   Sun, 29 Aug 2021 18:55:00 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        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>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Michael Petlan <mpetlan@...hat.com>,
        "Frank Ch. Eigler" <fche@...hat.com>,
        Song Liu <songliubraving@...com>, x86@...nel.org,
        Daniel Díaz <daniel.diaz@...aro.org>,
        Andrii Nakryiko <andriin@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org
Subject: Re: [PATCH v5 2/9] coresight: tmc-etr: Add barrier after updating
 AUX ring buffer

Hi Mathieu, Suzuki,

On Mon, Aug 09, 2021 at 07:14:00PM +0800, Leo Yan wrote:
> Since a memory barrier is required between AUX trace data store and
> aux_head store, and the AUX trace data is filled with memcpy(), it's
> sufficient to use smp_wmb() so can ensure the trace data is visible
> prior to updating aux_head.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>

Could you pick up patches 02 and 03 in this series?  Please note,
patch 02 has the review tag from Suzuki, but I didn't receive the
review tag for patch 03.

If anything need to follow up, just let me know.  Thanks!

> ---
>  drivers/hwtracing/coresight/coresight-tmc-etr.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index acdb59e0e661..13fd1fc730ed 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -1563,6 +1563,14 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
>  	 */
>  	if (etr_perf->snapshot)
>  		handle->head += size;
> +
> +	/*
> +	 * Ensure that the AUX trace data is visible before the aux_head
> +	 * is updated via perf_aux_output_end(), as expected by the
> +	 * perf ring buffer.
> +	 */
> +	smp_wmb();
> +
>  out:
>  	/*
>  	 * Don't set the TRUNCATED flag in snapshot mode because 1) the
> -- 
> 2.25.1
>