Fix torch.load(..., weights_only=True) for NT (#112516)

Found when looking into #112509
Pull Request resolved: https://github.com/pytorch/pytorch/pull/112516
Approved by: https://github.com/soulitzer

test/test_nestedtensor.py

@@ -2995,7 +2995,8 @@ class TestNestedTensorSubclass(TestCase):
 
     @dtypes(torch.float, torch.double, torch.half)
     @parametrize("requires_grad", [False, True])
-    def test_serialization(self, device, dtype, requires_grad):
+    @parametrize("weights_only", [False, True])
+    def test_serialization(self, device, dtype, requires_grad, weights_only):
 
         def compare_metadata(nt1, nt2):
             self.assertEqual(nt1._nested_tensor_size(), nt2._nested_tensor_size())
@@ -3008,7 +3009,7 @@ class TestNestedTensorSubclass(TestCase):
             buffer = io.BytesIO()
             serialized = torch.save(a, buffer)
             buffer.seek(0)
-            b = torch.load(buffer)
+            b = torch.load(buffer, weights_only=weights_only)
             # should be both conceptually equal and metadata equivalent
             self.assertEqual(a, b)
             compare_metadata(a, b)

torch/_tensor.py

@@ -376,7 +376,7 @@ class Tensor(torch._C.TensorBase):
                 self._nested_tensor_strides(),
                 self._nested_tensor_storage_offsets(),
             )
-            return (torch._nested_view_from_buffer, args_nested)
+            return (torch._utils._rebuild_nested_tensor, args_nested)
         elif (
             self.data_ptr() == 0
             and type(self) is not torch.Tensor

torch/_utils.py

@@ -304,6 +304,10 @@ def _rebuild_sparse_tensor(layout, data):
     raise NotImplementedError(f"rebuilding sparse tensor for layout {layout}")
 
 
+def _rebuild_nested_tensor(buffer, sizes, strides, storage_offsets):
+    return torch._nested_view_from_buffer(buffer, sizes, strides, storage_offsets)
+
+
 def _rebuild_device_tensor_from_numpy(data, dtype, device, requires_grad):
     tensor = torch.from_numpy(data).to(dtype=dtype, device=device)
     tensor.requires_grad = requires_grad

torch/_weights_only_unpickler.py

@@ -101,6 +101,7 @@ def _get_allowed_globals():
         torch._utils._rebuild_tensor_v2,
         torch._utils._rebuild_sparse_tensor,
         torch._utils._rebuild_meta_tensor_no_storage,
+        torch._utils._rebuild_nested_tensor,
     ]:
         rc[f"torch._utils.{f.__name__}"] = f