--- old/src/hotspot/share/runtime/sweeper.cpp	2018-09-23 20:45:25.744241981 +0200
+++ new/src/hotspot/share/runtime/sweeper.cpp	2018-09-23 20:45:25.442241998 +0200
@@ -247,6 +247,15 @@
 }
 
 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
+#ifdef ASSERT
+  if (ThreadLocalHandshakes) {
+    assert(Thread::current()->is_Code_cache_sweeper_thread(), "must be executed under CodeCache_lock and in sweeper thread");
+    assert_lock_strong(CodeCache_lock);
+  } else {
+    assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
+  }
+#endif
+
   // If we do not want to reclaim not-entrant or zombie methods there is no need
   // to scan stacks
   if (!MethodFlushing) {
@@ -295,7 +304,11 @@
   assert(!CodeCache_lock->owned_by_self(), "just checking");
   if (wait_for_stack_scanning()) {
     if (ThreadLocalHandshakes) {
-      CodeBlobClosure* code_cl = prepare_mark_active_nmethods();
+      CodeBlobClosure* code_cl;
+      {
+        MutexLockerEx ccl(CodeCache_lock, Mutex::_no_safepoint_check_flag);
+        code_cl = prepare_mark_active_nmethods();
+      }
       if (code_cl != NULL) {
         ThreadToCodeBlobClosure tcl(code_cl);
         Handshake::execute(&tcl);