Fix: post-load staging regression breaks offload meta/sharded_gpu modes (#38779)

python/sglang/srt/model_loader/post_load.py

@@ -134,13 +134,16 @@ def stage_module_for_post_load(
     owner_origins: dict[int, set[torch.device]] = {}
     module_origins: set[torch.device] = set()
     tensor_states: dict[int, _TensorState] = {}
+    # Offloader-parked parameters (see sglang.srt.utils.offloader) live on the
+    # meta device through post-load processing; kernels are expected to skip
+    # them. Pass them through untouched, matching the pre-staging behaviour.
+    meta_tensor_ids: set[int] = set()
 
     # snapshot and validate all state before moving any tensor
     for owner, registry_name, name, tensor in _iter_registered_tensors(module):
         if tensor.is_meta:
-            raise RuntimeError(
-                f"Cannot post-process meta tensor {type(owner).__name__}.{name}"
-            )
+            meta_tensor_ids.add(id(tensor))
+            continue
         state = tensor_states.get(id(tensor))
         if state is None:
             state = _TensorState(tensor, tensor.data, tensor.device)
@@ -167,6 +170,9 @@ def stage_module_for_post_load(
             next(iter(module_origins)) if len(module_origins) == 1 else None
         )
         for owner, registry_name, name, tensor in _iter_registered_tensors(module):
+            if id(tensor) in meta_tensor_ids:
+                # Parked by the offloader before staging; leave it as-is.
+                continue
             key = _slot_key(owner, registry_name, name)
             original_state = original_slots.get(key)
             if original_state is None:

test/registered/unit/test_quantization_post_load.py

@@ -140,18 +140,31 @@ class TestModulePostLoadValidation(unittest.TestCase):
 
         self.assertEqual(module.weight.device, PROCESS_DEVICE)
 
-    def test_rejects_meta_before_moving_other_state(self):
+    def test_parks_existing_meta_tensor_and_stages_the_rest(self):
         module = nn.Module()
         module.meta_weight = nn.Parameter(torch.empty(1, device="meta"))
         module.register_buffer("scale", torch.ones(1))
         scale_ptr = module.scale.data_ptr()
+        meta_weight = module.meta_weight
+
+        with stage_module_for_post_load(module, torch.device("cpu")):
+            # offloader-parked meta state passes through untouched
+            self.assertTrue(module.meta_weight.is_meta)
+            module.scale.add_(1)
+
+        self.assertIs(module.meta_weight, meta_weight)
+        self.assertTrue(module.meta_weight.is_meta)
+        self.assertEqual(module.scale.device.type, "cpu")
+        self.assertEqual(module.scale.data_ptr(), scale_ptr)
+        torch.testing.assert_close(module.scale, torch.full((1,), 2.0))
+
+    def test_rejects_meta_produced_by_post_load_processing(self):
+        module = nn.Module()
+        module.register_buffer("scale", torch.ones(1))
 
         with self.assertRaisesRegex(RuntimeError, "meta tensor"):
             with stage_module_for_post_load(module, torch.device("cpu")):
-                self.fail("context should not be entered")
-
-        self.assertEqual(module.scale.device.type, "cpu")
-        self.assertEqual(module.scale.data_ptr(), scale_ptr)
+                module.new_weight = nn.Parameter(torch.empty(1, device="meta"))
 
 
 if __name__ == "__main__":