--- old/src/hotspot/share/gc/z/zRootsIterator.cpp	2019-11-22 15:12:10.820584540 +0100
+++ new/src/hotspot/share/gc/z/zRootsIterator.cpp	2019-11-22 15:12:10.326568330 +0100
@@ -140,39 +140,46 @@
 
 class ZRootsIteratorCodeBlobClosure : public CodeBlobToOopClosure {
 private:
-  BarrierSetNMethod* _bs;
+  BarrierSetNMethod* const _bs;
+  const bool               _disarm_nmethods;
 
 public:
-  ZRootsIteratorCodeBlobClosure(OopClosure* cl) :
+  ZRootsIteratorCodeBlobClosure(OopClosure* cl, bool disarm_nmethods) :
     CodeBlobToOopClosure(cl, true /* fix_relocations */),
-    _bs(BarrierSet::barrier_set()->barrier_set_nmethod()) {}
+    _bs(BarrierSet::barrier_set()->barrier_set_nmethod()),
+    _disarm_nmethods(disarm_nmethods) {}
 
   virtual void do_code_blob(CodeBlob* cb) {
     nmethod* const nm = cb->as_nmethod_or_null();
     if (nm != NULL && nm->oops_do_try_claim()) {
       CodeBlobToOopClosure::do_code_blob(cb);
-      _bs->disarm(nm);
+      if (_disarm_nmethods) {
+        _bs->disarm(nm);
+      }
     }
   }
 };
 
 class ZRootsIteratorThreadClosure : public ThreadClosure {
 private:
-  ZRootsIteratorClosure* _cl;
+  ZRootsIteratorClosure* const _cl;
+  const bool                   _disarm_nmethods;
 
 public:
-  ZRootsIteratorThreadClosure(ZRootsIteratorClosure* cl) :
-      _cl(cl) {}
+  ZRootsIteratorThreadClosure(ZRootsIteratorClosure* cl, bool disarm_nmethods) :
+      _cl(cl),
+      _disarm_nmethods(disarm_nmethods) {}
 
   virtual void do_thread(Thread* thread) {
-    ZRootsIteratorCodeBlobClosure code_cl(_cl);
+    ZRootsIteratorCodeBlobClosure code_cl(_cl, _disarm_nmethods);
     thread->oops_do(_cl, ClassUnloading ? &code_cl : NULL);
     _cl->do_thread(thread);
   }
 };
 
-ZRootsIterator::ZRootsIterator(bool visit_jvmti_weak_export) :
+ZRootsIterator::ZRootsIterator(bool visit_jvmti_weak_export, bool disarm_nmethods) :
     _visit_jvmti_weak_export(visit_jvmti_weak_export),
+    _disarm_nmethods(disarm_nmethods),
     _universe(this),
     _object_synchronizer(this),
     _management(this),
@@ -240,7 +247,7 @@
 void ZRootsIterator::do_threads(ZRootsIteratorClosure* cl) {
   ZStatTimer timer(ZSubPhasePauseRootsThreads);
   ResourceMark rm;
-  ZRootsIteratorThreadClosure thread_cl(cl);
+  ZRootsIteratorThreadClosure thread_cl(cl, _disarm_nmethods);
   Threads::possibly_parallel_threads_do(true, &thread_cl);
 }