dma-buf/fence: add an lockdep_assert_held()

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1477339030-32657-1-git-send-email-robdclark@gmail.com

drivers/dma-buf/fence.c

@@ -68,6 +68,8 @@ int fence_signal_locked(struct fence *fence)
 	struct fence_cb *cur, *tmp;
 	int ret = 0;
 
+	lockdep_assert_held(fence->lock);
+
 	if (WARN_ON(!fence))
 		return -EINVAL;