drm/i915/execlists: Add a couple more validity checks to assert_pending()

Check the pending request submission is valid: that it at least has a
reference for the submission and that the request is on the active list.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191203152631.3107653-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -1303,6 +1303,9 @@ assert_pending_valid(const struct intel_engine_execlists *execlists,
 		unsigned long flags;
 		bool ok = true;
 
+		GEM_BUG_ON(!kref_read(&rq->fence.refcount));
+		GEM_BUG_ON(!i915_request_is_active(rq));
+
 		if (ce == rq->hw_context) {
 			GEM_TRACE_ERR("Dup context:%llx in pending[%zd]\n",
 				      ce->timeline->fence_context,