--- old/src/hotspot/share/runtime/synchronizer.cpp	2019-08-28 15:01:54.410961760 -0400
+++ new/src/hotspot/share/runtime/synchronizer.cpp	2019-08-28 15:01:54.238961766 -0400
@@ -1095,6 +1095,9 @@
 
 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
+  // The oops_do() phase does not overlap with monitor deflation
+  // so no need to update the ObjectMonitor's ref_count for this
+  // ObjectMonitor* use.
   ObjectMonitor* mid;
   for (mid = list; mid != NULL; mid = mid->_next_om) {
     if (mid->object() != NULL) {
@@ -2082,7 +2085,9 @@
     // mid is old (is not newly allocated and is not newly freed).
     if (mid->object() != NULL && mid->is_old() &&
         deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
-      // Deflation succeeded so update the in-use list.
+      // Deflation succeeded and already updated free_head_p and
+      // free_tail_p as needed. Finish the move to the local free list
+      // by unlinking mid from the global or per-thread in-use list.
       if (mid == *list_p) {
         *list_p = mid->_next_om;
       } else if (cur_mid_in_use != NULL) {
@@ -2250,7 +2255,7 @@
     deflated_count += local_deflated_count;
 
     if (free_head_p != NULL) {
-      // Move the scavenged ObjectMonitors to the global free list.
+      // Move the deflated ObjectMonitors to the global free list.
       guarantee(free_tail_p != NULL && local_deflated_count > 0, "free_tail_p=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(free_tail_p), local_deflated_count);
       assert(free_tail_p->_next_om == NULL, "invariant");