diff -r a6deb69743d4 -r 4cbfa5077d68 src/hotspot/os/posix/os_posix.cpp
--- a/src/hotspot/os/posix/os_posix.cpp	Mon Nov 25 12:32:07 2019 +0100
+++ b/src/hotspot/os/posix/os_posix.cpp	Mon Nov 25 12:32:40 2019 +0100
@@ -1998,7 +1998,7 @@
   // but only in the correctly written condition checking loops of ObjectMonitor,
   // Mutex/Monitor, Thread::muxAcquire and JavaThread::sleep
 
-  if (Atomic::xchg(1, &_event) >= 0) return;
+  if (Atomic::xchg(&_event, 1) >= 0) return;
 
   int status = pthread_mutex_lock(_mutex);
   assert_status(status == 0, status, "mutex_lock");
@@ -2046,7 +2046,7 @@
   // Return immediately if a permit is available.
   // We depend on Atomic::xchg() having full barrier semantics
   // since we are doing a lock-free update to _counter.
-  if (Atomic::xchg(0, &_counter) > 0) return;
+  if (Atomic::xchg(&_counter, 0) > 0) return;
 
   Thread* thread = Thread::current();
   assert(thread->is_Java_thread(), "Must be JavaThread");