@@ -577,6 +577,18 @@ static bool i915_guc_dequeue(struct intel_engine_cs *engine)
struct rb_node *rb;
bool submit = false;
+ /* After execlist_first is updated, the tasklet will be rescheduled.
+ *
+ * If we are currently running (inside the tasklet) and a third
+ * party queues a request and so updates engine->execlist_first under
+ * the spinlock (which we have elided), it will atomically set the
+ * TASKLET_SCHED flag causing the us to be re-executed and pick up
+ * the change in state (the update to TASKLET_SCHED incurs a memory
+ * barrier making this cross-cpu checking safe).
+ */
+ if (!READ_ONCE(engine->execlist_first))
+ return false;
+
spin_lock_irqsave(&engine->timeline->lock, flags);
rb = engine->execlist_first;
while (rb) {
@@ -403,6 +403,18 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
struct rb_node *rb;
bool submit = false;
+ /* After execlist_first is updated, the tasklet will be rescheduled.
+ *
+ * If we are currently running (inside the tasklet) and a third
+ * party queues a request and so updates engine->execlist_first under
+ * the spinlock (which we have elided), it will atomically set the
+ * TASKLET_SCHED flag causing the us to be re-executed and pick up
+ * the change in state (the update to TASKLET_SCHED incurs a memory
+ * barrier making this cross-cpu checking safe).
+ */
+ if (!READ_ONCE(engine->execlist_first))
+ return;
+
last = port->request;
if (last)
/* WaIdleLiteRestore:bdw,skl