drm/i915: Add a few asserts around handling of i915_request_is_active()

Let's assert that we only call the execute callbacks on making the
request active, and that we do not execute the request without calling
the callbacks.
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/20200529085809.23691-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_request.c

@@ -192,6 +192,7 @@ static void __notify_execute_cb(struct i915_request *rq)
 
 	lockdep_assert_held(&rq->lock);
 
+	GEM_BUG_ON(!i915_request_is_active(rq));
 	if (llist_empty(&rq->execute_cb))
 		return;
 
@@ -518,15 +519,15 @@ bool __i915_request_submit(struct i915_request *request)
 	if (!test_and_set_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags)) {
 		list_move_tail(&request->sched.link, &engine->active.requests);
 		clear_bit(I915_FENCE_FLAG_PQUEUE, &request->fence.flags);
+		__notify_execute_cb(request);
 	}
+	GEM_BUG_ON(!llist_empty(&request->execute_cb));
 
 	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags) &&
 	    !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags) &&
 	    !i915_request_enable_breadcrumb(request))
 		intel_engine_signal_breadcrumbs(engine);
 
-	__notify_execute_cb(request);
-
 	spin_unlock(&request->lock);
 
 	return result;