gh-149110: Fix memory ordering in take_ownership() for f_frame publication

Author: BHUVANSH855

Objects/frameobject.c

@@ -2399,10 +2399,15 @@ PyFrameObject*
 PyFrame_GetBack(PyFrameObject *frame)
 {
     assert(frame != NULL);
-    assert(!_PyFrame_IsIncomplete(frame->f_frame));
+    /* Use an acquire load so that if we observe the new f_frame pointer
+     * published by take_ownership()'s release store, we also observe
+     * new_frame->owner == FRAME_OWNED_BY_FRAME_OBJECT. */
+    _PyInterpreterFrame *f_frame =
+        (_PyInterpreterFrame *)_Py_atomic_load_ptr_acquire(&frame->f_frame);
+    assert(!_PyFrame_IsIncomplete(f_frame));
     PyFrameObject *back = frame->f_back;
     if (back == NULL) {
-        _PyInterpreterFrame *prev = frame->f_frame->previous;
+        _PyInterpreterFrame *prev = f_frame->previous;
         prev = _PyFrame_GetFirstComplete(prev);
         if (prev) {
             back = _PyFrame_GetFrameObject(prev);

Python/frame.c

@@ -69,7 +69,11 @@ take_ownership(PyFrameObject *f, _PyInterpreterFrame *frame)
      * observes the new f_frame pointer also sees owner = FRAME_OWNED_BY_FRAME_OBJECT,
      * causing _PyFrame_IsIncomplete() to short-circuit to false. */
     new_frame->owner = FRAME_OWNED_BY_FRAME_OBJECT;
-    f->f_frame = new_frame;
+    /* Publish f_frame with a release store so that any concurrent reader
+     * doing an acquire load of f_frame is guaranteed to also observe
+     * new_frame->owner == FRAME_OWNED_BY_FRAME_OBJECT (written above),
+     * satisfying the C11 happens-before relationship. */
+    _Py_atomic_store_ptr_release(&f->f_frame, new_frame);
     assert(!_PyFrame_IsIncomplete(new_frame));
     assert(f->f_back == NULL);
     _PyInterpreterFrame *prev = _PyFrame_GetFirstComplete(frame->previous);