--- old/src/hotspot/share/gc/g1/g1FreeIdSet.cpp	2019-11-21 11:57:10.466985522 +0100
+++ new/src/hotspot/share/gc/g1/g1FreeIdSet.cpp	2019-11-21 11:57:10.034978225 +0100
@@ -79,7 +79,7 @@
     index = head_index(old_head);
     assert(index < _size, "invariant");
     uintx new_head = make_head(_next[index], old_head);
-    new_head = Atomic::cmpxchg(new_head, &_head, old_head);
+    new_head = Atomic::cmpxchg(&_head, old_head, new_head);
     if (new_head == old_head) break;
     old_head = new_head;
   }
@@ -95,7 +95,7 @@
   while (true) {
     _next[index] = head_index(old_head);
     uintx new_head = make_head(index, old_head);
-    new_head = Atomic::cmpxchg(new_head, &_head, old_head);
+    new_head = Atomic::cmpxchg(&_head, old_head, new_head);
     if (new_head == old_head) break;
     old_head = new_head;
   }