--- a/src/hotspot/share/gc/parallel/mutableSpace.cpp	Mon Nov 25 12:32:40 2019 +0100
+++ b/src/hotspot/share/gc/parallel/mutableSpace.cpp	Mon Nov 25 12:33:15 2019 +0100
@@ -194,7 +194,7 @@
     HeapWord* obj = top();
     if (pointer_delta(end(), obj) >= size) {
       HeapWord* new_top = obj + size;
-      HeapWord* result = Atomic::cmpxchg(new_top, top_addr(), obj);
+      HeapWord* result = Atomic::cmpxchg(top_addr(), obj, new_top);
       // result can be one of two:
       //  the old top value: the exchange succeeded
       //  otherwise: the new value of the top is returned.
@@ -213,7 +213,7 @@
 // Try to deallocate previous allocation. Returns true upon success.
 bool MutableSpace::cas_deallocate(HeapWord *obj, size_t size) {
   HeapWord* expected_top = obj + size;
-  return Atomic::cmpxchg(obj, top_addr(), expected_top) == expected_top;
+  return Atomic::cmpxchg(top_addr(), expected_top, obj) == expected_top;
 }
 
 void MutableSpace::oop_iterate(OopIterateClosure* cl) {