--- old/src/hotspot/share/jfr/recorder/service/jfrPostBox.cpp	2019-11-21 11:58:02.511864602 +0100
+++ new/src/hotspot/share/jfr/recorder/service/jfrPostBox.cpp	2019-11-21 11:58:01.995855888 +0100
@@ -87,7 +87,7 @@
     const int current_msgs = Atomic::load(&_messages);
     // OR the new message
     const int exchange_value = current_msgs | new_messages;
-    const int result = Atomic::cmpxchg(exchange_value, &_messages, current_msgs);
+    const int result = Atomic::cmpxchg(&_messages, current_msgs, exchange_value);
     if (result == current_msgs) {
       return;
     }
@@ -139,7 +139,7 @@
 
 int JfrPostBox::collect() {
   // get pending and reset to 0
-  const int messages = Atomic::xchg(0, &_messages);
+  const int messages = Atomic::xchg(&_messages, 0);
   if (check_waiters(messages)) {
     _has_waiters = true;
     assert(JfrMsg_lock->owned_by_self(), "incrementing _msg_read_serial is protected by JfrMsg_lock");