bpo-45061: Detect Py_DECREF(Py_True) bug (pythonGH-28089)

vstinner · web-flow · commit 4300352000be · 2021-08-31T18:05:15.000+02:00
Add a deallocator to the bool type to detect refcount bugs in C
extensions which call Py_DECREF(Py_True) or Py_DECREF(Py_False) by
mistake.
diff --git a/Misc/NEWS.d/next/C API/2021-08-31-15-21-36.bpo-45061.ZH0HVe.rst b/Misc/NEWS.d/next/C API/2021-08-31-15-21-36.bpo-45061.ZH0HVe.rst
@@ -0,0 +1,3 @@
+Add a deallocator to the :class:`bool` type to detect refcount bugs in C
+extensions which call ``Py_DECREF(Py_True);`` or ``Py_DECREF(Py_False);`` by
+mistake. Patch by Victor Stinner.
diff --git a/Objects/boolobject.c b/Objects/boolobject.c
@@ -153,14 +153,21 @@ static PyNumberMethods bool_as_number = {
     0,                          /* nb_index */
 };
 
+static void _Py_NO_RETURN
+bool_dealloc(PyObject* Py_UNUSED(ignore))
+{
+    Py_FatalError("deallocating True or False likely caused by "
+                  "a refcount bug in a C extension");
+}
+
 /* The type object for bool.  Note that this cannot be subclassed! */
 
 PyTypeObject PyBool_Type = {
     PyVarObject_HEAD_INIT(&PyType_Type, 0)
     "bool",
     sizeof(struct _longobject),
     0,
-    0,                                          /* tp_dealloc */
+    bool_dealloc,                               /* tp_dealloc */
     0,                                          /* tp_vectorcall_offset */
     0,                                          /* tp_getattr */
     0,                                          /* tp_setattr */
diff --git a/Objects/object.c b/Objects/object.c
@@ -1560,14 +1560,11 @@ none_repr(PyObject *op)
     return PyUnicode_FromString("None");
 }
 
-/* ARGUSED */
 static void _Py_NO_RETURN
-none_dealloc(PyObject* ignore)
+none_dealloc(PyObject* Py_UNUSED(ignore))
 {
-    /* This should never get called, but we also don't want to SEGV if
-     * we accidentally decref None out of existence.
-     */
-    Py_FatalError("deallocating None");
+    Py_FatalError("deallocating None likely caused by a refcount bug "
+                  "in a C extension");
 }
 
 static PyObject *

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Add a deallocator to the :class:`bool` type to detect refcount bugs in C
	`2`	+extensions which call ``Py_DECREF(Py_True);`` or ``Py_DECREF(Py_False);`` by
	`3`	`+mistake. Patch by Victor Stinner.`
Original file line number	Diff line number	Diff line change
`@@ -1560,14 +1560,11 @@ none_repr(PyObject *op)`
`1560`	`1560`	`return PyUnicode_FromString("None");`
`1561`	`1561`	`}`
`1562`	`1562`
`1563`		`-/* ARGUSED */`
`1564`	`1563`	`static void _Py_NO_RETURN`
`1565`		`-none_dealloc(PyObject* ignore)`
	`1564`	`+none_dealloc(PyObject* Py_UNUSED(ignore))`
`1566`	`1565`	`{`
`1567`		`- /* This should never get called, but we also don't want to SEGV if`
`1568`		`- * we accidentally decref None out of existence.`
`1569`		`- */`
`1570`		`- Py_FatalError("deallocating None");`
	`1566`	`+ Py_FatalError("deallocating None likely caused by a refcount bug "`
	`1567`	`+ "in a C extension");`
`1571`	`1568`	`}`
`1572`	`1569`
`1573`	`1570`	`static PyObject *`