[Intel-gfx] [PATCH] drm/i915/gt: Report the currently active execlists request

[Chris Wilson]

Since commit 22b7a426bbe1 ("drm/i915/execlists: Preempt-to-busy"), we
prune the engine->active.requests list prior to preemption, thus
removing the trace of the currently executing request. If that request
hangs rather than be preempted, we conclude that no active request was
on the GPU. Fortunately, this only impacts our debugging, and not our
means of hang detection or recovery.

References: 22b7a426bbe1 ("drm/i915/execlists: Preempt-to-busy")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 drivers/gpu/drm/i915/gt/intel_engine_cs.c | 29 ++++++++++++++++++-----
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 06ff7695fa29..93878fd42a7a 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -1643,7 +1643,7 @@ static bool match_ring(struct i915_request *rq)
 struct i915_request *
 intel_engine_find_active_request(struct intel_engine_cs *engine)
 {
-	struct i915_request *request, *active = NULL;
+	struct i915_request *rq, *active = NULL;
 
 	/*
 	 * We are called by the error capture, reset and to dump engine
@@ -1657,18 +1657,35 @@ intel_engine_find_active_request(struct intel_engine_cs *engine)
 	 * we only care about the snapshot of this moment.
 	 */
 	lockdep_assert_held(&engine->active.lock);
-	list_for_each_entry(request, &engine->active.requests, sched.link) {
-		if (i915_request_completed(request))
+
+	rcu_read_lock();
+	rq = execlists_active(&engine->execlists);
+	if (rq) {
+		struct intel_timeline *tl = rq->context->timeline;
+
+		list_for_each_entry_continue_reverse(rq, &tl->requests, link) {
+			if (i915_request_completed(rq))
+				break;
+
+			active = rq;
+		}
+	}
+	rcu_read_unlock();
+	if (active)
+		return active;
+
+	list_for_each_entry(rq, &engine->active.requests, sched.link) {
+		if (i915_request_completed(rq))
 			continue;
 
-		if (!i915_request_started(request))
+		if (!i915_request_started(rq))
 			continue;
 
 		/* More than one preemptible request may match! */
-		if (!match_ring(request))
+		if (!match_ring(rq))
 			continue;
 
-		active = request;
+		active = rq;
 		break;
 	}
 
-- 
2.25.0