Re: [PATCH 07/25] coresight: perf: Validate the live context through its path

[James Clark <james.clark@linaro.org>]

On 15/09/2026 16:48, Leo Yan wrote:
> etm_event_get_ctxt_path() returns a path only when the per-CPU
> context has published event data and that data contains a path for the
> current CPU. Perf PMU callbacks run on the same CPU in atomic context,
> and only the normal stop clears the event data. A returned path therefore
> establishes that the pause and stop callbacks have a live ETM context.
> 
> The AUX handle has a separate lifetime. It can be absent after an AUX
> transaction could not be restarted while the CoreSight path still needs
> to be paused or disabled. The handle is acquired for the callback event
> before event data is published, and another ETM event cannot replace it
> while the published context remains live. Thus any active handle belongs
> to that context, and etm_event_update_buffer() uses perf_get_aux() to
> determine whether it remains valid.
> 
> Remove the redundant comparisons of the handle with the event and event
> data, together with the redundant event_data check. Use the path to
> validate the ETM context lifetime and perf_get_aux() to validate the AUX
> handle lifetime.
> 
> Assisted-by: Codex:gpt-6
> Signed-off-by: Leo Yan <leo.yan@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-etm-perf.c | 15 ---------------
>   1 file changed, 15 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index afd22fd4a851e600ab69fd5b6883e6f8518b2cab..c7454da5c881c4a8eea5cc77902c9113c297096e 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -698,9 +698,6 @@ static void etm_event_pause(struct coresight_path *path,
>   	if (coresight_is_percpu_sink(sink))
>   		return;
>   
> -	if (WARN_ON_ONCE(handle->event != event))
> -		return;
> -
>   	event_data = READ_ONCE(ctxt->event_data);
>   	etm_event_update_buffer(handle, event_data, sink, PERF_EF_UPDATE);
>   
> @@ -728,14 +725,6 @@ static void etm_event_stop(struct perf_event *event, int mode)
>   		return;
>   	}
>   
> -	/*
> -	 * If we still have access to the event_data via handle,
> -	 * confirm that we haven't messed up the tracking.
> -	 */
> -	if (handle->event &&
> -	    WARN_ON(perf_get_aux(handle) != ctxt->event_data))
> -		return;
> -
>   	event_data = READ_ONCE(ctxt->event_data);
>   	/* Clear the event_data as this ETM is stopping the trace. */
>   	WRITE_ONCE(ctxt->event_data, NULL);
> @@ -743,10 +732,6 @@ static void etm_event_stop(struct perf_event *event, int mode)
>   	if (event->hw.state == PERF_HES_STOPPED)
>   		return;
>   
> -	/* We must have a valid event_data for a running event */
> -	if (WARN_ON(!event_data))
> -		return;
> -
>   	source = coresight_get_source(path);
>   	sink = coresight_get_sink(path);
>   	if (!source || !sink)
> 
Reviewed-by: James Clark <james.clark@linaro.org>