gh-151763: Fix dealloc clears the in-flight exception in subtype_dealloc

Misc/NEWS.d/next/Core_and_Builtins/2026-07-11-14-39-38.gh-issue-151763.nlYxAk.rst

@@ -0,0 +1,2 @@
+Fixed a bug in free-threaded builds where the active exception could be
+unexpectedly cleared during subtype deallocation in ``subtype_dealloc()``.

Objects/typeobject.c

@@ -2833,6 +2833,13 @@ subtype_dealloc(PyObject *self)
         }
     }
 
+    /* Save the current exception: clear_slots() and the dict/base-dealloc
+           below decref arbitrary attribute values, which may clear
+           tstate->current_exception (gh-89373).  Mirroring slot_tp_finalize(). */
+     PyThreadState *tstate = _PyThreadState_GET();
+     PyObject *exc = _PyErr_GetRaisedException(tstate);   /* preserve in-flight exception */
+
+
     /*  Clear slots up to the nearest base with a different tp_dealloc */
     base = type;
     while ((basedealloc = base->tp_dealloc) == subtype_dealloc) {
@@ -2882,6 +2889,9 @@ subtype_dealloc(PyObject *self)
     if (type_needs_decref) {
         _Py_DECREF_TYPE(type);
     }
+
+    /* Restore the saved exception (see save above). */
+    _PyErr_SetRaisedException(tstate, exc);
 }
 
 static PyTypeObject *solid_base(PyTypeObject *type);