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SubjectRe: [RFC 09/11] coresight: etm-perf: Disable the path before capturing the trace data
On 11/10/20 12:45 PM, Anshuman Khandual wrote:
> perf handle structure needs to be shared with the TRBE IRQ handler for
> capturing trace data and restarting the handle. There is a probability
> of an undefined reference based crash when etm event is being stopped
> while a TRBE IRQ also getting processed. This happens due the release
> of perf handle via perf_aux_output_end(). This stops the sinks via the
> link before releasing the handle, which will ensure that a simultaneous
> TRBE IRQ could not happen.
> Signed-off-by: Anshuman Khandual <>
> ---
> This might cause problem with traditional sink devices which can be
> operated in both sysfs and perf mode. This needs to be addressed
> correctly. One option would be to move the update_buffer callback
> into the respective sink devices. e.g, disable().
> drivers/hwtracing/coresight/coresight-etm-perf.c | 2 ++
> 1 file changed, 2 insertions(+)
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index 534e205..1a37991 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -429,7 +429,9 @@ static void etm_event_stop(struct perf_event *event, int mode)
> size = sink_ops(sink)->update_buffer(sink, handle,
> event_data->snk_config);
> + coresight_disable_path(path);
> perf_aux_output_end(handle, size);
> + return;
> }

As you mentioned, this is not ideal where another session could be triggered on
the sink from a different ETM (not for per-CPU sink) in a different mode before
you collect the buffer. I believe the best option is to leave the
update_buffer() to disable_hw. This would need to pass on the "handle" to the

That way the races can be handled inside the sinks. Also, this aligns the
perf mode of the sinks with that of the sysfs mode.


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