[autograd] match 0-dim gradients device type regardless of subclassness (#160165)

xmfan · pytorchmergebot · commit c8205cb35435 · 2025-08-11T17:57:32.000Z
Not sure if there some subclasses where the outer.dim() == 0 but you wouldn't want to move it? FIXES #160084 Pull Request resolved: #160165 Approved by: https://github.com/ezyang, https://github.com/albanD
diff --git a/test/dynamo/test_repros.py b/test/dynamo/test_repros.py
@@ -7673,6 +7673,31 @@ def forward(self, x):
         out2 = torch.compile(model, backend="eager")(input.clone())
         self.assertEqual(out1, out2)
 
+    @requires_cuda
+    def test_zero_dim_param_mixed_device_grad(self):
+        # cpu 0-dim params with cuda grads
+        # https://github.com/pytorch/pytorch/issues/160084
+        class RegressionModel(torch.nn.Module):
+            def __init__(self, a=0, b=0):
+                super().__init__()
+                self.a = torch.nn.Parameter(torch.tensor(a).float())
+                self.b = torch.nn.Parameter(torch.tensor(b).float())
+
+            def forward(self, x):
+                return x * self.a + self.b
+
+        model = RegressionModel()
+        model.forward = torch.compile(
+            model.forward, backend="aot_eager", fullgraph=True
+        )
+        inputs = torch.randn(4, 10).to("cuda")
+        out = model(inputs)
+        out.sum().backward()
+        self.assertIsNotNone(model.a.grad)
+        self.assertIsNotNone(model.b.grad)
+        self.assertEqual(model.a.grad.device, torch.device("cpu"))
+        self.assertEqual(model.b.grad.device, torch.device("cpu"))
+
     def test_filter_warnings(self):
         x = torch.ones(2, 2, requires_grad=True)
 
diff --git a/test/test_autograd.py b/test/test_autograd.py
@@ -12396,6 +12396,29 @@ def test_resize_version_bump(self, device):
         x.resize_as_(y)
         self.assertEqual(x._version, 2)
 
+    @unittest.skipIf(not torch.accelerator.is_available(), "requires accelerator")
+    def test_zero_dim_param_mixed_device_grad(self, device):
+        # cpu 0-dim params with an accelerator device grad
+        # https://github.com/pytorch/pytorch/issues/160084
+        class RegressionModel(torch.nn.Module):
+            def __init__(self, a=0, b=0):
+                super().__init__()
+                self.a = torch.nn.Parameter(torch.tensor(a).float())
+                self.b = torch.nn.Parameter(torch.tensor(b).float())
+
+            def forward(self, x):
+                return x * self.a + self.b
+
+        # Keep the model on cpu as we do want to test the mixed cpu/accelerator behavior here
+        model = RegressionModel()
+        inputs = torch.randn(4, 10, device=device)
+        out = model(inputs)
+        out.sum().backward()
+        self.assertIsNotNone(model.a.grad)
+        self.assertIsNotNone(model.b.grad)
+        self.assertEqual(model.a.grad.device, torch.device("cpu"))
+        self.assertEqual(model.b.grad.device, torch.device("cpu"))
+
 
 class TestAllowMutationOnSaved(TestCase):
     def assertClonedLenEqual(self, ctx, n):
diff --git a/test/test_python_dispatch.py b/test/test_python_dispatch.py
@@ -1,7 +1,6 @@
 # Owner(s): ["module: __torch_dispatch__"]
 # ruff: noqa: F841
 
-import logging
 import pickle
 import sys
 import tempfile
@@ -1718,49 +1717,6 @@ def __torch_dispatch__(self, func, types, args=(), kwargs=None):
                 self.assertEqual(s.device_index, 2)
                 self.assertEqual(s.device_type, 3)
 
-    def test_subclass_autograd_device_check(self) -> None:
-        class NonWrapperSubclass(torch.Tensor):
-            elem: torch.Tensor
-
-            __slots__ = ["elem"]
-
-            @staticmethod
-            def __new__(cls, elem, *args, **kwargs):
-                # Wrong device here!
-                r = torch.Tensor._make_subclass(
-                    cls, elem.to("meta"), elem.requires_grad
-                )
-                # ...the real tensor is held as an element on the tensor.
-                r.elem = elem
-                return r
-
-            @classmethod
-            def __torch_dispatch__(cls, func, types, args=(), kwargs=None):
-                def unwrap(e):
-                    return e.elem if isinstance(e, NonWrapperSubclass) else e
-
-                def wrap(e):
-                    return NonWrapperSubclass(e) if isinstance(e, torch.Tensor) else e
-
-                rs = tree_map(
-                    wrap, func(*tree_map(unwrap, args), **tree_map(unwrap, kwargs))
-                )
-                logging.getLogger("NonWrapperSubclass").info(
-                    f"{func.__module__}.{func.__name__}",  # noqa: G004
-                    args,
-                    kwargs,
-                    rs,
-                )
-                return rs
-
-        x = NonWrapperSubclass(torch.tensor([3.0, 4.0], requires_grad=True))
-        y = torch.randn(2, requires_grad=True)
-        z = x * y
-        self.assertIsInstance(z, NonWrapperSubclass)
-        z.sum().backward(torch.tensor(1))
-        self.assertEqual(x.grad, y)
-        self.assertEqual(y.grad, x)
-
     def test_none_wrapping(self):
         # A Tensor subclass that returns None when doing add
         # See LoggingTensor above for more details on the subclass
diff --git a/torch/csrc/autograd/engine.cpp b/torch/csrc/autograd/engine.cpp
@@ -979,13 +979,13 @@ static void validate_outputs_impl(
     }
 
     if (grad.device() != metadata.device()) {
-      // quick hack for: https://github.com/pytorch/pytorch/issues/65016 but
-      // should be eventually removed
-      if (!(metadata.is_tensor_subclass() ||
-            grad.unsafeGetTensorImpl()->is_python_dispatch())) {
-        if (grad.dim() == 0) {
-          grad = grad.to(metadata.device());
-        } else {
+      if (grad.dim() == 0) {
+        grad = grad.to(metadata.device());
+      } else {
+        // quick hack for: https://github.com/pytorch/pytorch/issues/65016 but
+        // should be eventually removed
+        if (!(metadata.is_tensor_subclass() ||
+              grad.unsafeGetTensorImpl()->is_python_dispatch())) {
           std::stringstream ss;
           ss << "invalid gradient at index " << i << " - expected device ";
           ss << metadata.device() << " but got " << grad.device();
