linux-kernel - Re: [PATCH 4/5] coresight: trbe: Move irq

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Message-ID: <390617ae-c5bd-b73a-c48c-e62b7f5330ca@arm.com>
Date:   Thu, 15 Jul 2021 08:53:46 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        al.grant@....com, leo.yan@...aro.org, mathieu.poirier@...aro.org,
        mike.leach@...aro.org, peterz@...radead.org, Tamas.Zsoldos@....com,
        will@...nel.org
Subject: Re: [PATCH 4/5] coresight: trbe: Move irq_work queue processing



On 7/12/21 5:08 PM, Suzuki K Poulose wrote:
> The TRBE driver issues the irq_work_run() to ensure that
> any pending disable event callback has been processed. But this
> is done before we mark the AUX buffer as TRUNCATED, making
> the call pointless. Move the call after the current handle
> has been closed.

So there is a possibility that a disable event gets missed before
the buffer is marked TRUNCATED ? But even then would not another
disable event be triggered again subsequently ? Just trying to
understand what is the actual problem because of the current
placement of irq_work_run() ?

> 
> Fixes: 3fbf7f011f24 ("coresight: sink: Add TRBE driver")
> Reported-by: Tamas Zsoldos <Tamas.Zsoldos@....com>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Leo Yan <leo.yan@...aro.org>
> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  drivers/hwtracing/coresight/coresight-trbe.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index ec38cf17b693..c0c264264427 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -723,6 +723,14 @@ static void trbe_handle_overflow(struct perf_output_handle *handle)
>  	perf_aux_output_flag(handle, PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW |
>  				     PERF_AUX_FLAG_TRUNCATED);
>  	perf_aux_output_end(handle, size);
> +
> +	/*
> +	 * Ensure perf callbacks have completed. Since we
> +	 * always TRUNCATE the buffer on IRQ, the event
> +	 * is scheduled to be disabled. Make sure that happens
> +	 * as soon as possible.
> +	 */
> +	irq_work_run();
>  }
>  
>  static bool is_perf_trbe(struct perf_output_handle *handle)
> @@ -777,12 +785,6 @@ static irqreturn_t arm_trbe_irq_handler(int irq, void *dev)
>  	if (!is_perf_trbe(handle))
>  		return IRQ_NONE;
>  
> -	/*
> -	 * Ensure perf callbacks have completed, which may disable
> -	 * the trace buffer in response to a TRUNCATION flag.
> -	 */
> -	irq_work_run();
> -
>  	act = trbe_get_fault_act(status);
>  	switch (act) {
>  	case TRBE_FAULT_ACT_WRAP:
>