gh-152951 - Fix double DECREF when newblock fails during deque.extend calls (#152961)

stestagg · web-flow · commit a90576d72c8a · 2026-07-03T20:43:24.000+03:00
diff --git a/Misc/NEWS.d/next/Library/2026-07-03-14-54-33.gh-issue-152951.u8tPCI.rst b/Misc/NEWS.d/next/Library/2026-07-03-14-54-33.gh-issue-152951.u8tPCI.rst
@@ -0,0 +1,2 @@
+:class:`collections.deque` prevent rare crash when calling ``extend`` under
+high memory pressure conditions.
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
@@ -512,7 +512,6 @@ deque_extend_impl(dequeobject *deque, PyObject *iterable)
     iternext = *Py_TYPE(it)->tp_iternext;
     while ((item = iternext(it)) != NULL) {
         if (deque_append_lock_held(deque, item, maxlen) == -1) {
-            Py_DECREF(item);
             Py_DECREF(it);
             return NULL;
         }

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+:class:`collections.deque` prevent rare crash when calling ``extend`` under
	`2`	`+high memory pressure conditions.`
Original file line number	Diff line number	Diff line change
`@@ -512,7 +512,6 @@ deque_extend_impl(dequeobject deque, PyObject iterable)`
`512`	`512`	`iternext = *Py_TYPE(it)->tp_iternext;`
`513`	`513`	`while ((item = iternext(it)) != NULL) {`
`514`	`514`	`if (deque_append_lock_held(deque, item, maxlen) == -1) {`
`515`		`- Py_DECREF(item);`
`516`	`515`	`Py_DECREF(it);`
`517`	`516`	`return NULL;`
`518`	`517`	`}`