[diffusion] CI: fix picklingerror for diffusion models using diffusers backend (#20854)

python/sglang/multimodal_gen/registry.py

@@ -11,6 +11,7 @@ import dataclasses
 import importlib
 import os
 import pkgutil
+import sys
 from functools import lru_cache
 from typing import (
     TYPE_CHECKING,
@@ -381,6 +382,19 @@ def _get_diffusers_model_info(
                     ],
                     bases=(DiffusersGenericPipelineConfig,),
                 )
+                # make_dataclass sets __module__="types"; fix for pickle.
+                pipeline_config_cls.__module__ = (
+                    DiffusersGenericPipelineConfig.__module__
+                )
+                pipeline_config_cls.__qualname__ = (
+                    DiffusersGenericPipelineConfig.__qualname__
+                )
+                parent_module = sys.modules[DiffusersGenericPipelineConfig.__module__]
+                setattr(
+                    parent_module,
+                    DiffusersGenericPipelineConfig.__name__,
+                    pipeline_config_cls,
+                )
                 logger.debug(
                     "Inherited task_type=%s from native config for diffusers backend",
                     native_task_type.name,