drm/nouveau: require reservations for nouveau_fence_sync and nouveau_bo_fence

This will ensure we always hold the required lock when calling those functions.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Acked-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -1463,6 +1463,8 @@ nouveau_bo_fence(struct nouveau_bo *nvbo, struct nouveau_fence *fence)
 	struct nouveau_fence *new_fence = nouveau_fence_ref(fence);
 	struct nouveau_fence *old_fence = NULL;
 
+	lockdep_assert_held(&nvbo->bo.resv->lock.base);
+
 	spin_lock(&nvbo->bo.bdev->fence_lock);
 	old_fence = nvbo->bo.sync_obj;
 	nvbo->bo.sync_obj = new_fence;

drivers/gpu/drm/nouveau/nouveau_display.c

@@ -717,6 +717,9 @@ nouveau_crtc_page_flip(struct drm_crtc *crtc, struct drm_framebuffer *fb,
 	}
 
 	mutex_lock(&cli->mutex);
+	ret = ttm_bo_reserve(&new_bo->bo, true, false, false, NULL);
+	if (ret)
+		goto fail_unpin;
 
 	/* synchronise rendering channel with the kernel's channel */
 	spin_lock(&new_bo->bo.bdev->fence_lock);
@@ -724,12 +727,18 @@ nouveau_crtc_page_flip(struct drm_crtc *crtc, struct drm_framebuffer *fb,
 	spin_unlock(&new_bo->bo.bdev->fence_lock);
 	ret = nouveau_fence_sync(fence, chan);
 	nouveau_fence_unref(&fence);
-	if (ret)
+	if (ret) {
+		ttm_bo_unreserve(&new_bo->bo);
 		goto fail_unpin;
+	}
 
-	ret = ttm_bo_reserve(&old_bo->bo, true, false, false, NULL);
-	if (ret)
-		goto fail_unpin;
+	if (new_bo != old_bo) {
+		ttm_bo_unreserve(&new_bo->bo);
+
+		ret = ttm_bo_reserve(&old_bo->bo, true, false, false, NULL);
+		if (ret)
+			goto fail_unpin;
+	}
 
 	/* Initialize a page flip struct */
 	*s = (struct nouveau_page_flip_state)