[Intel-gfx] [PATCH 4/6] drm/i915/gt: Check the virtual still matches upon locking

[Chris Wilson]

If another sibling is able to claim the virtual request, by the time we
inspect the request under the lock if may no longer match the local
engine.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2877
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_execlists_submission.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
index f02e3ae10d28..a5b442683c18 100644
--- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
+++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
@@ -1016,6 +1016,9 @@ static bool virtual_matches(const struct virtual_engine *ve,
 {
 	const struct intel_engine_cs *inflight;
 
+	if (!rq)
+		return false;
+
 	if (!(rq->execution_mask & engine->mask)) /* We peeked too soon! */
 		return false;
 
@@ -1423,8 +1426,8 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 		spin_lock(&ve->base.active.lock);
 
 		rq = ve->request;
-		if (unlikely(!rq)) /* lost the race to a sibling */
-			goto unlock;
+		if (unlikely(!virtual_matches(ve, rq, engine)))
+			goto unlock; /* lost the race to a sibling */
 
 		GEM_BUG_ON(rq->engine != &ve->base);
 		GEM_BUG_ON(rq->context != &ve->context);
@@ -1434,8 +1437,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 			break;
 		}
 
-		GEM_BUG_ON(!virtual_matches(ve, rq, engine));
-
 		if (last && !can_merge_rq(last, rq)) {
 			spin_unlock(&ve->base.active.lock);
 			spin_unlock(&engine->active.lock);
-- 
2.20.1