diff -r 13588c901957 -r 9cf78a70fa4f src/hotspot/share/oops/constantPool.cpp
--- a/src/hotspot/share/oops/constantPool.cpp	Thu Oct 17 20:27:44 2019 +0100
+++ b/src/hotspot/share/oops/constantPool.cpp	Thu Oct 17 20:53:35 2019 +0100
@@ -556,7 +556,8 @@
     Handle h_loader (thread, loader);
     Klass* k = SystemDictionary::find(name, h_loader, h_prot, thread);
 
-    if (k != NULL) {
+    // Avoid constant pool verification at a safepoint, which takes the Module_lock.
+    if (k != NULL && !SafepointSynchronize::is_at_safepoint()) {
       // Make sure that resolving is legal
       EXCEPTION_MARK;
       // return NULL if verification fails
@@ -760,6 +761,10 @@
     // return the method type signature in the error message
     message = this_cp->method_type_signature_at(which);
     break;
+  case JVM_CONSTANT_Dynamic:
+    // return the name of the condy in the error message
+    message = this_cp->uncached_name_ref_at(which);
+    break;
   default:
     ShouldNotReachHere();
   }
@@ -862,7 +867,7 @@
   if (cache_index >= 0) {
     result_oop = this_cp->resolved_references()->obj_at(cache_index);
     if (result_oop != NULL) {
-      if (oopDesc::equals(result_oop, Universe::the_null_sentinel())) {
+      if (result_oop == Universe::the_null_sentinel()) {
         DEBUG_ONLY(int temp_index = (index >= 0 ? index : this_cp->object_to_cp_index(cache_index)));
         assert(this_cp->tag_at(temp_index).is_dynamic_constant(), "only condy uses the null sentinel");
         result_oop = NULL;
@@ -1092,12 +1097,12 @@
     } else {
       // Return the winning thread's result.  This can be different than
       // the result here for MethodHandles.
-      if (oopDesc::equals(old_result, Universe::the_null_sentinel()))
+      if (old_result == Universe::the_null_sentinel())
         old_result = NULL;
       return old_result;
     }
   } else {
-    assert(!oopDesc::equals(result_oop, Universe::the_null_sentinel()), "");
+    assert(result_oop != Universe::the_null_sentinel(), "");
     return result_oop;
   }
 }
@@ -1150,7 +1155,7 @@
 oop ConstantPool::string_at_impl(const constantPoolHandle& this_cp, int which, int obj_index, TRAPS) {
   // If the string has already been interned, this entry will be non-null
   oop str = this_cp->resolved_references()->obj_at(obj_index);
-  assert(!oopDesc::equals(str, Universe::the_null_sentinel()), "");
+  assert(str != Universe::the_null_sentinel(), "");
   if (str != NULL) return str;
   Symbol* sym = this_cp->unresolved_string_at(which);
   str = StringTable::intern(sym, CHECK_(NULL));