From fa127d9b20720b70c6481ee9c19693714c428446 Mon Sep 17 00:00:00 2001
From: zeshengzong <zesheng.zong@outlook.com>
Date: Tue, 16 Sep 2025 12:07:46 +0000
Subject: [PATCH] Fix `LBFGS` wolfe max iteration (#161488)

Fixes #91581 , based on #135026

## Test Result

```bash
pytest test/test_optim.py

.........
========================== 1473 passed, 242 skipped in 2412.49s (0:40:12) ===========================
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/161488
Approved by: https://github.com/albanD
---
 test/test_optim.py   | 28 ++++++++++++++++++++++++++++
 torch/optim/lbfgs.py |  9 ++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/test/test_optim.py b/test/test_optim.py
index 6dd23d6328c..de185725b5c 100644
--- a/test/test_optim.py
+++ b/test/test_optim.py
@@ -2305,6 +2305,34 @@ class TestOptimRenewed(TestCase):
             for state in optim.state.values():
                 self.assertGreater(len(state), 0)
 
+    @parametrize("dtype", [torch.float32])
+    def test_step_iteration(self, device, dtype):
+        def _get_model_and_input_tensor(device, dtype):
+            model = torch.nn.Sequential(
+                torch.nn.Conv2d(4, 2, 1, stride=2),
+                torch.nn.BatchNorm2d(2, eps=1e-05, momentum=0.1),
+            )
+            input = torch.rand(1, 4, 16, 16, device=device, dtype=dtype)
+            model.to(dtype=dtype, device=device)
+            return model, input
+
+        counter = 0
+
+        def fwd_bwd(optim, mod, i):
+            nonlocal counter
+            counter += 1
+            optim.zero_grad()
+            loss = mod(i).sum()
+            loss.backward()
+            return loss
+
+        model, input = _get_model_and_input_tensor(device, dtype)
+        optimizer = torch.optim.LBFGS(
+            model.parameters(), max_iter=1, max_eval=5, line_search_fn="strong_wolfe"
+        )
+        optimizer.step(functools.partial(fwd_bwd, optimizer, model, input))
+        self.assertEqual(counter, 6)
+
 
 instantiate_device_type_tests(TestOptimRenewed, globals(), allow_mps=True)
 
diff --git a/torch/optim/lbfgs.py b/torch/optim/lbfgs.py
index 674aaaf2688..09f5f2ca8c8 100644
--- a/torch/optim/lbfgs.py
+++ b/torch/optim/lbfgs.py
@@ -442,7 +442,14 @@ class LBFGS(Optimizer):
                         return self._directional_evaluate(closure, x, t, d)
 
                     loss, flat_grad, t, ls_func_evals = _strong_wolfe(
-                        obj_func, x_init, t, d, loss, flat_grad, gtd
+                        obj_func,
+                        x_init,
+                        t,
+                        d,
+                        loss,
+                        flat_grad,
+                        gtd,
+                        max_ls=max_eval - current_evals,
                     )
                 self._add_grad(t, d)
                 opt_cond = flat_grad.abs().max() <= tolerance_grad