Re: [PATCH 4/5] coresight: trbe: Move irq_work queue processing

[Anshuman Khandual <anshuman.khandual@arm.com>]

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@arm.com>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: Will Deacon <will@kernel.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.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:
>