8273505: runtime/cds/appcds/loaderConstraints/DynamicLoaderConstraintsTest.java#default-cl crashed with SIGSEGV in MetaspaceShared::link_shared_classes

Reviewed-by: iklam, minqi

src/hotspot/share/cds/metaspaceShared.cpp

@@ -584,18 +584,19 @@ void VM_PopulateDumpSharedSpace::doit() {
 
 class CollectCLDClosure : public CLDClosure {
   GrowableArray<ClassLoaderData*> _loaded_cld;
+  GrowableArray<Handle> _loaded_cld_handles; // keep the CLDs alive
+  Thread* _current_thread;
 public:
-  CollectCLDClosure() {}
+  CollectCLDClosure(Thread* thread) : _current_thread(thread) {}
   ~CollectCLDClosure() {
     for (int i = 0; i < _loaded_cld.length(); i++) {
       ClassLoaderData* cld = _loaded_cld.at(i);
-      cld->dec_keep_alive();
     }
   }
   void do_cld(ClassLoaderData* cld) {
     if (!cld->is_unloading()) {
-      cld->inc_keep_alive();
       _loaded_cld.append(cld);
+      _loaded_cld_handles.append(Handle(_current_thread, cld->holder_phantom()));
     }
   }
 
@@ -641,11 +642,10 @@ bool MetaspaceShared::link_class_for_cds(InstanceKlass* ik, TRAPS) {
 }
 
 void MetaspaceShared::link_shared_classes(TRAPS) {
-  // Collect all loaded ClassLoaderData.
-  ResourceMark rm;
-
   LambdaFormInvokers::regenerate_holder_classes(CHECK);
-  CollectCLDClosure collect_cld;
+
+  // Collect all loaded ClassLoaderData.
+  CollectCLDClosure collect_cld(THREAD);
   {
     // ClassLoaderDataGraph::loaded_cld_do requires ClassLoaderDataGraph_lock.
     // We cannot link the classes while holding this lock (or else we may run into deadlock).

src/hotspot/share/classfile/classLoaderData.cpp

@@ -302,9 +302,7 @@ bool ClassLoaderData::try_claim(int claim) {
 // it is being defined, therefore _keep_alive is not volatile or atomic.
 void ClassLoaderData::inc_keep_alive() {
   if (has_class_mirror_holder()) {
-    if (!Arguments::is_dumping_archive()) {
-      assert(_keep_alive > 0, "Invalid keep alive increment count");
-    }
+    assert(_keep_alive > 0, "Invalid keep alive increment count");
     _keep_alive++;
   }
 }