8308181: Generational ZGC: Remove CLDG_lock from old gen root scanning

Reviewed-by: ayang, aboldtch

Author: fisk

src/hotspot/share/gc/z/zGeneration.cpp

@@ -1421,13 +1421,7 @@ class ZRemapYoungRootsTask : public ZTask {
       _cl_colored(),
       _cld_cl(&_cl_colored),
       _thread_cl(),
-      _nm_cl() {
-    ClassLoaderDataGraph_lock->lock();
-  }
-
-  ~ZRemapYoungRootsTask() {
-    ClassLoaderDataGraph_lock->unlock();
-  }
+      _nm_cl() {}
 
   virtual void work() {
     {

src/hotspot/share/gc/z/zMark.cpp

@@ -829,13 +829,7 @@ class ZMarkOldRootsTask : public ZTask {
       _cl_colored(),
       _cld_cl(&_cl_colored),
       _thread_cl(),
-      _nm_cl() {
-    ClassLoaderDataGraph_lock->lock();
-  }
-
-  ~ZMarkOldRootsTask() {
-    ClassLoaderDataGraph_lock->unlock();
-  }
+      _nm_cl() {}
 
   virtual void work() {
     {