[PATCH 04/25] coresight: perf: End AUX output when an event is throttled

[Leo Yan <leo.yan@arm.com>]

Since commit 9734e25fbf5a ("perf: Fix the throttle logic for a
group"), the perf core stops every event in a throttled group by calling
the PMU stop callback with flags set to zero:

  perf_event_throttle()
    `> event->pmu->stop(event, 0)

The ETM perf stop callback only ends the AUX output handle when
PERF_EF_UPDATE was set. For throttling with mode is zero, it skips to
end the AUX handle. When the event is later unthrottled and ETM tracing
is started again, perf_aux_output_begin() sees the perf handle is nest
enabled and triggers a warning:

  [  181.161897] ------------[ cut here ]------------
  [  181.161906] WARNING: kernel/events/ring_buffer.c:415 at perf_aux_output_begin+0x1dc/0x1f0, CPU#0:2
  [  181.234120] arm-scmi arm-scmi.1.auto: timed out in resp(caller: do_xfer+0x1a0/0x558)
  [  181.234223] cpufreq: __target_index: Failed to change cpu frequency: -110
  [  181.286675] Modules linked in: panfrost tda9950 hdlcd tda998x drm_shmem_helper drm_client_lib cect
  [  181.314139] CPU: 0 UID: 0 PID: 352 Comm: perf Not tainted 7.1.0-rc1-00058-gdca922e019dd-dirty #11
  [  181.323915] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, B5
  [  181.334732] pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  [  181.341721] pc : perf_aux_output_begin+0x1dc/0x1f0
  [  181.346547] lr : perf_aux_output_begin+0x9c/0x1f0
  [  181.351280] sp : ffff800080003be0
  [  181.354606] x29: ffff800080003be0 x28: ffff0008023fc000 x27: ffff4b45d287f000
  [  181.361789] x26: ffff0009764787a8 x25: 0000000000000000 x24: ffff00080dc99710
  [  181.368970] x23: ffffb4c334553000 x22: 0000000000000001 x21: ffff00080dc99710
  [  181.376151] x20: ffff0009764787a8 x19: ffff000801cc6000 x18: 00000000ffffffff
  [  181.383332] x17: 0000000000000000 x16: ffffb4c3a118c998 x15: 0000000000000000
  [  181.390512] x14: 00003d0900000000 x13: 00000001ffff006e x12: 696765625f747570
  [  181.397692] x11: ffffb4c3a52758d8 x10: 0000000000000108 x9 : ffffb4c3a117f620
  [  181.404873] x8 : ffff800080003a58 x7 : ffff000808de4000 x6 : 00000000000fffff
  [  181.412053] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
  [  181.419232] x2 : 0000000000000007 x1 : 0000000000000000 x0 : 0000000000000007
  [  181.426411] Call trace:
  [  181.428868]  perf_aux_output_begin+0x1dc/0x1f0 (P)
  [  181.433692]  etm_event_start+0xdc/0x290 [coresight]
  [  181.438665]  perf_event_unthrottle+0x70/0xa8
  [  181.442964]  perf_event_unthrottle_group+0x40/0x170
  [  181.447871]  perf_adjust_freq_unthr_events+0x178/0x1a8
  [  181.453038]  perf_adjust_freq_unthr_context+0x74/0xf8
  [  181.458120]  perf_event_task_tick+0xa8/0x290
  [  181.462418]  sched_tick+0x144/0x2c8
  [  181.465937]  update_process_times+0xc0/0x198

Reproduce this with the command:

  perf record -a -e cs_etm/aux-action=start-paused/k \
	-e cycles/aux-action=pause,period=3000/ \
	-e cycles/aux-action=resume,period=1500/ -- sleep 10

An update of the sink buffer is unnecessary when PERF_EF_UPDATE is not
set, but the AUX output operation must still be terminated. End it with
a size of zero so that a later restart can acquire a new handle.

Fixes: 9734e25fbf5a ("perf: Fix the throttle logic for a group")
Signed-off-by: Leo Yan <leo.yan@arm.com>
---
 drivers/hwtracing/coresight/coresight-etm-perf.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 09b21a711a8764ea429d712890265c84648e889e..a45f69f39f175f3044322b25fe5413fb97154496 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -748,13 +748,16 @@ static void etm_event_stop(struct perf_event *event, int mode)
 	 * handle due to lack of buffer space), we don't
 	 * have to do anything here.
 	 */
-	if (handle->event && (mode & PERF_EF_UPDATE)) {
+	if (!handle->event)
+		goto out;
+
+	if (mode & PERF_EF_UPDATE) {
 		if (WARN_ON_ONCE(handle->event != event))
-			return;
+			goto out;
 
 		/* update trace information */
 		if (!sink_ops(sink)->update_buffer)
-			return;
+			goto out;
 
 		size = sink_ops(sink)->update_buffer(sink, handle,
 					      event_data->snk_config);
@@ -773,8 +776,11 @@ static void etm_event_stop(struct perf_event *event, int mode)
 			perf_aux_output_end(handle, size);
 		else
 			WARN_ON(size);
+	} else {
+		perf_aux_output_end(handle, 0);
 	}
 
+out:
 	/* Disabling the path make its elements available to other sessions */
 	coresight_disable_path(path);
 }

-- 
2.34.1