From 5b0d27e4698e555fccbcd1b0f62ddc80e5dd4a14 Mon Sep 17 00:00:00 2001
From: Matt Page <mpage@meta.com>
Date: Thu, 14 Mar 2024 15:37:43 -0700
Subject: [PATCH 1/2] Simplify weakref creation logic

Since 3.12 allocating a GC object cannot immediately trigger GC. This
allows us to simplify the logic for creating the canonical callback-less
weakref.
---
 Objects/weakrefobject.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

diff --git a/Objects/weakrefobject.c b/Objects/weakrefobject.c
index df74be6aba7244..5ef3689e33fded 100644
--- a/Objects/weakrefobject.c
+++ b/Objects/weakrefobject.c
@@ -801,24 +801,14 @@ PyWeakref_NewRef(PyObject *ob, PyObject *callback)
     if (result != NULL)
         Py_INCREF(result);
     else {
-        /* Note: new_weakref() can trigger cyclic GC, so the weakref
-           list on ob can be mutated.  This means that the ref and
-           proxy pointers we got back earlier may have been collected,
-           so we need to compute these values again before we use
-           them. */
+        /* We do not need to recompute ref/proxy; new_weakref() cannot
+           trigger GC.
+        */
         result = new_weakref(ob, callback);
         if (result != NULL) {
-            get_basic_refs(*list, &ref, &proxy);
             if (callback == NULL) {
                 if (ref == NULL)
                     insert_head(result, list);
-                else {
-                    /* Someone else added a ref without a callback
-                       during GC.  Return that one instead of this one
-                       to avoid violating the invariants of the list
-                       of weakrefs for ob. */
-                    Py_SETREF(result, (PyWeakReference*)Py_NewRef(ref));
-                }
             }
             else {
                 PyWeakReference *prev;

From 56956ecf51479c47b358b2d51b00b32a5582642c Mon Sep 17 00:00:00 2001
From: Matt Page <mpage@meta.com>
Date: Thu, 14 Mar 2024 16:16:36 -0700
Subject: [PATCH 2/2] Ref is always NULL if callback is NULL

---
 Objects/weakrefobject.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Objects/weakrefobject.c b/Objects/weakrefobject.c
index 5ef3689e33fded..6264b1825eda73 100644
--- a/Objects/weakrefobject.c
+++ b/Objects/weakrefobject.c
@@ -807,8 +807,8 @@ PyWeakref_NewRef(PyObject *ob, PyObject *callback)
         result = new_weakref(ob, callback);
         if (result != NULL) {
             if (callback == NULL) {
-                if (ref == NULL)
-                    insert_head(result, list);
+                assert(ref == NULL);
+                insert_head(result, list);
             }
             else {
                 PyWeakReference *prev;