[3.13] gh-134163: fix: exec('_testcapi.set_nomemory(0)') hang in new repl 3.13

Lib/test/test_repl.py

@@ -98,6 +98,36 @@ def test_no_memory(self):
         # Exit code 120: Py_FinalizeEx() failed to flush stdout and stderr.
         self.assertIn(p.returncode, (1, 120))
 
+    @cpython_only
+    # Python built with Py_TRACE_REFS fail with a fatal error in
+    # _PyRefchain_Trace() on memory allocation error.
+    @unittest.skipIf(support.Py_TRACE_REFS, 'cannot test Py_TRACE_REFS build')
+    def test_exec_set_nomemory_hang(self):
+        import_module("_testcapi")
+        # gh-134163: Test case that triggers no memory hang condition
+        # The frame_lasti need to upper 257,
+        # because when calling PyLong_FromLong, malloc is not invoked,
+        # so no MemError is triggered
+        # we need to warm up the memory to reproduce the issue
+        warmup_code = "a = list(range(0, 1))\n" * 20
+        user_input = warmup_code + dedent("""
+            try:
+                import _testcapi
+                _testcapi.set_nomemory(0)
+                b = list(range(1000, 2000))
+            except Exception as e:
+                import traceback
+                traceback.print_exc()
+            """)
+        p = spawn_repl()
+        with SuppressCrashReport():
+            p.stdin.write(user_input)
+        output = kill_python(p)
+
+        self.assertIn(p.returncode, (0, 1, 120))
+        self.assertGreater(len(output), 0)  # At minimum, should not hang
+        self.assertIn("MemoryError", output)
+
     @cpython_only
     def test_multiline_string_parsing(self):
         # bpo-39209: Multiline string tokens need to be handled in the tokenizer

Misc/NEWS.d/next/Core_and_Builtins/2025-09-04-11-52-23.gh-issue-134163.EqKyn8.rst

@@ -0,0 +1 @@
+Fix a hang when the process is out of memory inside an exception handler.

Python/ceval.c

@@ -912,7 +912,11 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
                 int frame_lasti = _PyInterpreterFrame_LASTI(frame);
                 PyObject *lasti = PyLong_FromLong(frame_lasti);
                 if (lasti == NULL) {
-                    goto exception_unwind;
+                    // Instead of going back to exception_unwind (which would cause
+                    // infinite recursion), directly exit to let the original exception
+                    // propagate up and hopefully be handled at a higher level.
+                    _PyFrame_SetStackPointer(frame, stack_pointer);
+                    goto exit_unwind;
                 }
                 PUSH(lasti);
             }