[3.12] gh-111777: Fix assertion errors on incorrectly still-tracked GC object destruction (GH-111778) (#111989)

miss-islington · Yhg1s · web-flow · commit 13ca1f02a409 · 2023-11-12T00:44:24.000Z
gh-111777: Fix assertion errors on incorrectly still-tracked GC object destruction (GH-111778) In PyObject_GC_Del, in Py_DEBUG mode, when warning about GC objects that were not properly untracked before starting destruction, take care to untrack the object _before_ warning, to avoid triggering a GC run and causing the problem the code tries to warn about. Also make sure to save and restore any pending exceptions, which the warning would otherwise clobber or trigger an assertion error on. (cherry picked from commit ce6a533) Co-authored-by: T. Wouters <thomas@python.org>
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
@@ -2381,14 +2381,16 @@ PyObject_GC_Del(void *op)
     size_t presize = _PyType_PreHeaderSize(((PyObject *)op)->ob_type);
     PyGC_Head *g = AS_GC(op);
     if (_PyObject_GC_IS_TRACKED(op)) {
+        gc_list_remove(g);
 #ifdef Py_DEBUG
+        PyObject *exc = PyErr_GetRaisedException();
         if (PyErr_WarnExplicitFormat(PyExc_ResourceWarning, "gc", 0,
                                      "gc", NULL, "Object of type %s is not untracked before destruction",
                                      ((PyObject*)op)->ob_type->tp_name)) {
             PyErr_WriteUnraisable(NULL);
         }
+        PyErr_SetRaisedException(exc);
 #endif
-        gc_list_remove(g);
     }
     GCState *gcstate = get_gc_state();
     if (gcstate->generations[0].count > 0) {
