8316711: SEGV in LoaderConstraintTable::find_loader_constraint after JDK-8310874

Reviewed-by: dcubed, iklam

Author: coleenp

src/hotspot/share/classfile/loaderConstraints.cpp

@@ -448,6 +448,7 @@ InstanceKlass* LoaderConstraintTable::find_constrained_klass(Symbol* name,
 void LoaderConstraintTable::remove_failed_loaded_klass(InstanceKlass* klass,
                                                        ClassLoaderData* loader) {
 
+  MutexLocker ml(SystemDictionary_lock);
   Symbol* name = klass->name();
   LoaderConstraint *p = find_loader_constraint(name, loader);
   if (p != nullptr && p->klass() != nullptr && p->klass() == klass) {

src/hotspot/share/classfile/systemDictionary.cpp

@@ -1524,12 +1524,10 @@ InstanceKlass* SystemDictionary::find_or_define_instance_class(Symbol* class_nam
     assert(defined_k != nullptr, "Should have a klass if there's no exception");
     k->class_loader_data()->add_to_deallocate_list(k);
   } else if (HAS_PENDING_EXCEPTION) {
+    // Remove this InstanceKlass from the LoaderConstraintTable if added.
+    LoaderConstraintTable::remove_failed_loaded_klass(k, class_loader_data(class_loader));
     assert(defined_k == nullptr, "Should not have a klass if there's an exception");
     k->class_loader_data()->add_to_deallocate_list(k);
-
-    // Also remove this InstanceKlass from the LoaderConstraintTable if added.
-    MutexLocker ml(SystemDictionary_lock);
-    LoaderConstraintTable::remove_failed_loaded_klass(k, class_loader_data(class_loader));
   }
   return defined_k;
 }