[PATCH 17/24] gtrace: Unify default sink selection across CPUs in perf setup

[Zane Leung]

In gtrace_setup_aux(), remember the sink found for the first CPU and
pass it to gtrace_create_path() for the remaining CPUs so they share a
compatible default sink. Clear a CPU from the mask when no path can be
built for it and abort when no sink is reachable at all.
---
 drivers/hwtracing/gtrace/gtrace-perf.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/gtrace/gtrace-perf.c b/drivers/hwtracing/gtrace/gtrace-perf.c
index 3c8b620df5a8..9b874daa807f 100644
--- a/drivers/hwtracing/gtrace/gtrace-perf.c
+++ b/drivers/hwtracing/gtrace/gtrace-perf.c
@@ -109,6 +109,7 @@ static void *gtrace_setup_aux(struct perf_event *event, void **pages,
 			       int nr_pages, bool overwrite)
 {
 	struct gtrace_event_data *event_data = NULL;
+	struct gtrace_component *sink = NULL;
 	struct page **pagelist;
 	int cpu = event->cpu, i;
 	cpumask_t *mask;
@@ -120,7 +121,7 @@ static void *gtrace_setup_aux(struct perf_event *event, void **pages,
 	INIT_WORK(&event_data->work, free_event_data);
 	mask = &event_data->mask;
 	/*
-	 * Create the path for each CPU in the mask. In case of any failure skip the CPU
+	 * Create the path for each CPU in the mask. In case of any failure clear the CPU
 	 */
 	for_each_cpu(cpu, mask) {
 		struct gtrace_component *src;
@@ -132,16 +133,28 @@ static void *gtrace_setup_aux(struct perf_event *event, void **pages,
 			continue;
 		}
 
-		path = gtrace_create_path(src, NULL, GTRACE_COMPONENT_MODE_PERF);
+		path = gtrace_create_path(src, sink, GTRACE_COMPONENT_MODE_PERF);
 		if (IS_ERR(path)) {
 			cpumask_clear_cpu(cpu, mask);
 			continue;
 		}
 
+		/*
+		 * The first found sink is saved here and passed to
+		 * gtrace_create_path() to check whether the remaining sources
+		 * have a compatible default sink.
+		 */
+		if (!sink)
+			sink = gtrace_path_sink(path);
+
 		path->event = event;
 		*gtrace_event_cpu_path_ptr(event_data, cpu) = path;
 	}
 
+	/* no sink found for any CPU - cannot trace */
+	if (!sink)
+		goto err;
+
 	/* If we don't have any CPUs ready for tracing, abort */
 	cpu = cpumask_first(&event_data->mask);
 	if (cpu >= nr_cpu_ids)
-- 
2.34.1