drm/i915: Unref old_obj on get_fence_reg() error path

Remember to release the local reference if we fail to wait on
the rendering.

(Also whilst in the vicinity add some whitespace so that the phasing of
the operations is clearer.)
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NEric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_gem.c

@@ -2267,8 +2267,6 @@ i915_gem_object_get_fence_reg(struct drm_gem_object *obj)
 				    fence_list) {
 			old_obj = old_obj_priv->obj;
 
-			reg = &dev_priv->fence_regs[old_obj_priv->fence_reg];
-
 			if (old_obj_priv->pin_count)
 				continue;
 
@@ -2290,8 +2288,11 @@ i915_gem_object_get_fence_reg(struct drm_gem_object *obj)
 			 */
 			i915_gem_object_flush_gpu_write_domain(old_obj);
 			ret = i915_gem_object_wait_rendering(old_obj);
-			if (ret != 0)
+			if (ret != 0) {
+				drm_gem_object_unreference(old_obj);
 				return ret;
+			}
+
 			break;
 		}
 
@@ -2299,10 +2300,14 @@ i915_gem_object_get_fence_reg(struct drm_gem_object *obj)
 		 * Zap this virtual mapping so we can set up a fence again
 		 * for this object next time we need it.
 		 */
-		i915_gem_release_mmap(reg->obj);
+		i915_gem_release_mmap(old_obj);
+
 		i = old_obj_priv->fence_reg;
+		reg = &dev_priv->fence_regs[i];
+
 		old_obj_priv->fence_reg = I915_FENCE_REG_NONE;
 		list_del_init(&old_obj_priv->fence_list);
+
 		drm_gem_object_unreference(old_obj);
 	}