On Tue, Apr 01, 2025 at 03:35:44PM +0100, Mike Leach wrote:
[...]
-static void etm_event_pause(struct coresight_device *csdev, +static void etm_event_pause(struct perf_event *event,
struct coresight_device *csdev, struct etm_ctxt *ctxt){
int cpu = smp_processor_id();struct coresight_device *sink;struct perf_output_handle *handle = &ctxt->handle;struct coresight_path *path;unsigned long size;if (!ctxt->event_data) return; /* Stop tracer */ coresight_pause_source(csdev);path = etm_event_cpu_path(ctxt->event_data, cpu);sink = coresight_get_sink(path);if (WARN_ON_ONCE(!sink))return;/** The per CPU sink has own interrupt handling, it might have* race condition with updating buffer on AUX trace pause if* it is invoked from NMI. To avoid the race condition,* disallows updating buffer for the per CPU sink case.*/if (coresight_is_percpu_sink(sink))return;if (WARN_ON_ONCE(handle->event != event))return;if (!sink_ops(sink)->update_buffer)return;size = sink_ops(sink)->update_buffer(sink, handle,ctxt->event_data->snk_config);I believe we keep the sink disabled/stopped in update_buffer. We need to turn it back ON after the "buffer update". May be we could use a flag to update_buffer() to indicate this is "pause" triggered update.
Thanks for pointing out, Suzuki.
I will fix it in next spin.
The sink is stopped to read data, but also important is the enable/disable refcount. The only time that "update_buffer" will read is if the sink has a refcount == 1. These are ultimately controlled by enable/disable path - which will not occur during pause/resume operations.
Hi Mike,
My understanding is: if a sink is shared by multiple CPUs, e.g. a Perf session with CPU mode or system wide mode, then we cannot arbitrarily disable sink and update buffer, otherwise, it might cause hardware lockup issue.
For per-thread mode, the refcount == 1, we can take chance to update buffer, right?
Thanks, Leo