diff -r cd496c5a3823 -r bffba8d6611a src/hotspot/share/runtime/thread.cpp
--- a/src/hotspot/share/runtime/thread.cpp	Sun Aug 25 19:09:22 2019 +0200
+++ b/src/hotspot/share/runtime/thread.cpp	Mon Aug 26 13:09:14 2019 +0200
@@ -3075,6 +3075,17 @@
 // if vm exit occurs during initialization). These cases can all be accounted
 // for such that this method never returns NULL.
 const char* JavaThread::get_thread_name() const {
+#ifdef ASSERT
+  // early safepoints can hit while current thread does not yet have TLS
+  if (!SafepointSynchronize::is_at_safepoint()) {
+    Thread *cur = Thread::current();
+    if (!(cur->is_Java_thread() && cur == this)) {
+      // Current JavaThreads are allowed to get their own name without
+      // the Threads_lock.
+      assert_locked_or_safepoint(Threads_lock);
+    }
+  }
+#endif // ASSERT
   return get_thread_name_string();
 }