--- a/src/hotspot/share/classfile/classLoaderData.cpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/classfile/classLoaderData.cpp	Wed Aug 08 15:24:21 2018 -0400
@@ -95,7 +95,7 @@
   ClassLoaderDataGraph::_head = _the_null_class_loader_data;
   assert(_the_null_class_loader_data->is_the_null_class_loader_data(), "Must be");
 
-  LogTarget(Debug, class, loader, data) lt;
+  LogTarget(Trace, class, loader, data) lt;
   if (lt.is_enabled()) {
     ResourceMark rm;
     LogStream ls(lt);
@@ -595,7 +595,7 @@
 void ClassLoaderData::unload() {
   _unloading = true;
 
-  LogTarget(Debug, class, loader, data) lt;
+  LogTarget(Trace, class, loader, data) lt;
   if (lt.is_enabled()) {
     ResourceMark rm;
     LogStream ls(lt);
@@ -606,7 +606,7 @@
 
   // Some items on the _deallocate_list need to free their C heap structures
   // if they are not already on the _klasses list.
-  unload_deallocate_list();
+  free_deallocate_list_C_heap_structures();
 
   // Tell serviceability tools these classes are unloading
   // after erroneous classes are released.
@@ -849,7 +849,7 @@
 }
 
 // Add this metadata pointer to be freed when it's safe.  This is only during
-// class unloading because Handles might point to this metadata field.
+// a safepoint which checks if handles point to this metadata field.
 void ClassLoaderData::add_to_deallocate_list(Metadata* m) {
   // Metadata in shared region isn't deleted.
   if (!m->is_shared()) {
@@ -858,6 +858,8 @@
       _deallocate_list = new (ResourceObj::C_HEAP, mtClass) GrowableArray<Metadata*>(100, true);
     }
     _deallocate_list->append_if_missing(m);
+    log_debug(class, loader, data)("deallocate added for %s", m->print_value_string());
+    ClassLoaderDataGraph::set_should_clean_deallocate_lists();
   }
 }
 
@@ -891,8 +893,44 @@
       assert(!m->is_klass() || !((InstanceKlass*)m)->is_scratch_class(),
              "scratch classes on this list should be dead");
       // Also should assert that other metadata on the list was found in handles.
+      // Some cleaning remains.
+      ClassLoaderDataGraph::set_should_clean_deallocate_lists();
+    }
+  }
+}
+
+void ClassLoaderDataGraph::clean_deallocate_lists(bool walk_previous_versions) {
+  uint loaders_processed = 0;
+  for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {
+    // is_alive check will be necessary for concurrent class unloading.
+    if (cld->is_alive()) {
+      // clean metaspace
+      if (walk_previous_versions) {
+        cld->classes_do(InstanceKlass::purge_previous_versions);
+      }
+      cld->free_deallocate_list();
+      loaders_processed++;
     }
   }
+  log_debug(class, loader, data)("clean_deallocate_lists: loaders processed %u %s",
+                                 loaders_processed, walk_previous_versions ? "walk_previous_versions" : "");
+}
+
+void ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces() {
+  assert(SafepointSynchronize::is_at_safepoint(), "must only be called at safepoint");
+
+  _should_clean_deallocate_lists = false; // assume everything gets cleaned
+
+  // Mark metadata seen on the stack so we can delete unreferenced entries.
+  // Walk all metadata, including the expensive code cache walk, only for class redefinition.
+  // The MetadataOnStackMark walk during redefinition saves previous versions if it finds old methods
+  // on the stack or in the code cache, so we only have to repeat the full walk if
+  // they were found at that time.
+  // TODO: have redefinition clean old methods out of the code cache.  They still exist in some places.
+  bool walk_all_metadata = InstanceKlass::has_previous_versions_and_reset();
+
+  MetadataOnStackMark md_on_stack(walk_all_metadata);
+  clean_deallocate_lists(walk_all_metadata);
 }
 
 // This is distinct from free_deallocate_list.  For class loader data that are
@@ -900,7 +938,7 @@
 // scratch or error classes so that unloading events aren't triggered for these
 // classes. The metadata is removed with the unloading metaspace.
 // There isn't C heap memory allocated for methods, so nothing is done for them.
-void ClassLoaderData::unload_deallocate_list() {
+void ClassLoaderData::free_deallocate_list_C_heap_structures() {
   // Don't need lock, at safepoint
   assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");
   assert(is_unloading(), "only called for ClassLoaderData that are unloading");
@@ -910,7 +948,6 @@
   // Go backwards because this removes entries that are freed.
   for (int i = _deallocate_list->length() - 1; i >= 0; i--) {
     Metadata* m = _deallocate_list->at(i);
-    assert (!m->on_stack(), "wouldn't be unloading if this were so");
     _deallocate_list->remove_at(i);
     if (m->is_constantPool()) {
       ((ConstantPool*)m)->release_C_heap_structures();
@@ -1026,6 +1063,8 @@
 ClassLoaderData* ClassLoaderDataGraph::_saved_head = NULL;
 
 bool ClassLoaderDataGraph::_should_purge = false;
+bool ClassLoaderDataGraph::_should_clean_deallocate_lists = false;
+bool ClassLoaderDataGraph::_safepoint_cleanup_needed = false;
 bool ClassLoaderDataGraph::_metaspace_oom = false;
 
 // Add a new class loader data node to the list.  Assign the newly created
@@ -1056,7 +1095,7 @@
     cld->set_next(next);
     ClassLoaderData* exchanged = Atomic::cmpxchg(cld, list_head, next);
     if (exchanged == next) {
-      LogTarget(Debug, class, loader, data) lt;
+      LogTarget(Trace, class, loader, data) lt;
       if (lt.is_enabled()) {
         ResourceMark rm;
         LogStream ls(lt);
@@ -1337,7 +1376,10 @@
 
 // Move class loader data from main list to the unloaded list for unloading
 // and deallocation later.
-bool ClassLoaderDataGraph::do_unloading(bool clean_previous_versions) {
+bool ClassLoaderDataGraph::do_unloading(bool do_cleaning) {
+
+  // Indicate whether safepoint cleanup is needed.
+  _safepoint_cleanup_needed |= do_cleaning;
 
   ClassLoaderData* data = _head;
   ClassLoaderData* prev = NULL;
@@ -1345,15 +1387,6 @@
   uint loaders_processed = 0;
   uint loaders_removed = 0;
 
-  // Mark metadata seen on the stack only so we can delete unneeded entries.
-  // Only walk all metadata, including the expensive code cache walk, for Full GC
-  // and only if class redefinition and if there's previous versions of
-  // Klasses to delete.
-  bool walk_all_metadata = clean_previous_versions &&
-                           JvmtiExport::has_redefined_a_class() &&
-                           InstanceKlass::has_previous_versions_and_reset();
-  MetadataOnStackMark md_on_stack(walk_all_metadata);
-
   // Save previous _unloading pointer for CMS which may add to unloading list before
   // purging and we don't want to rewalk the previously unloaded class loader data.
   _saved_unloading = _unloading;
@@ -1361,11 +1394,6 @@
   data = _head;
   while (data != NULL) {
     if (data->is_alive()) {
-      // clean metaspace
-      if (walk_all_metadata) {
-        data->classes_do(InstanceKlass::purge_previous_versions);
-      }
-      data->free_deallocate_list();
       prev = data;
       data = data->next();
       loaders_processed++;

--- a/src/hotspot/share/classfile/classLoaderData.hpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/classfile/classLoaderData.hpp	Wed Aug 08 15:24:21 2018 -0400
@@ -79,6 +79,12 @@
   static ClassLoaderData* _saved_head;
   static ClassLoaderData* _saved_unloading;
   static bool _should_purge;
+
+  // Set if there's anything to purge in the deallocate lists or previous versions
+  // during a safepoint after class unloading in a full GC.
+  static bool _should_clean_deallocate_lists;
+  static bool _safepoint_cleanup_needed;
+
   // OOM has been seen in metaspace allocation. Used to prevent some
   // allocations until class unloading
   static bool _metaspace_oom;
@@ -88,6 +94,7 @@
 
   static ClassLoaderData* add_to_graph(Handle class_loader, bool anonymous);
   static ClassLoaderData* add(Handle class_loader, bool anonymous);
+
  public:
   static ClassLoaderData* find_or_create(Handle class_loader);
   static void purge();
@@ -116,7 +123,13 @@
   static void packages_unloading_do(void f(PackageEntry*));
   static void loaded_classes_do(KlassClosure* klass_closure);
   static void classes_unloading_do(void f(Klass* const));
-  static bool do_unloading(bool clean_previous_versions);
+  static bool do_unloading(bool do_cleaning);
+
+  // Expose state to avoid logging overhead in safepoint cleanup tasks.
+  static inline bool should_clean_metaspaces_and_reset();
+  static void set_should_clean_deallocate_lists() { _should_clean_deallocate_lists = true; }
+  static void clean_deallocate_lists(bool purge_previous_versions);
+  static void walk_metadata_and_clean_metaspaces();
 
   // dictionary do
   // Iterate over all klasses in dictionary, but
@@ -297,8 +310,8 @@
   void packages_do(void f(PackageEntry*));
 
   // Deallocate free list during class unloading.
-  void free_deallocate_list();      // for the classes that are not unloaded
-  void unload_deallocate_list();    // for the classes that are unloaded
+  void free_deallocate_list();                      // for the classes that are not unloaded
+  void free_deallocate_list_C_heap_structures();    // for the classes that are unloaded
 
   // Allocate out of this class loader data
   MetaWord* allocate(size_t size);

--- a/src/hotspot/share/classfile/classLoaderData.inline.hpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/classfile/classLoaderData.inline.hpp	Wed Aug 08 15:24:21 2018 -0400
@@ -27,6 +27,7 @@
 
 #include "classfile/classLoaderData.hpp"
 #include "classfile/javaClasses.hpp"
+#include "oops/instanceKlass.hpp"
 #include "oops/oop.inline.hpp"
 #include "oops/oopHandle.inline.hpp"
 #include "oops/weakHandle.inline.hpp"
@@ -92,4 +93,10 @@
   Atomic::sub(count, &_num_array_classes);
 }
 
+bool ClassLoaderDataGraph::should_clean_metaspaces_and_reset() {
+  bool do_cleaning = _safepoint_cleanup_needed;
+  _safepoint_cleanup_needed = false;  // reset
+  return (do_cleaning && _should_clean_deallocate_lists) || InstanceKlass::has_previous_versions();
+}
+
 #endif // SHARE_VM_CLASSFILE_CLASSLOADERDATA_INLINE_HPP

--- a/src/hotspot/share/code/nmethod.cpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/code/nmethod.cpp	Wed Aug 08 15:24:21 2018 -0400
@@ -1540,6 +1540,7 @@
         }
       } else if (iter.type() == relocInfo::virtual_call_type) {
         // Check compiledIC holders associated with this nmethod
+        ResourceMark rm;
         CompiledIC *ic = CompiledIC_at(&iter);
         if (ic->is_icholder_call()) {
           CompiledICHolder* cichk = ic->cached_icholder();

--- a/src/hotspot/share/oops/constantPool.cpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/oops/constantPool.cpp	Wed Aug 08 15:24:21 2018 -0400
@@ -2490,9 +2490,9 @@
   if (has_preresolution()) st->print("/preresolution");
   if (operands() != NULL)  st->print("/operands[%d]", operands()->length());
   print_address_on(st);
-  st->print(" for ");
-  pool_holder()->print_value_on(st);
   if (pool_holder() != NULL) {
+    st->print(" for ");
+    pool_holder()->print_value_on(st);
     bool extra = (pool_holder()->constants() != this);
     if (extra)  st->print(" (extra)");
   }

--- a/src/hotspot/share/oops/instanceKlass.cpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/oops/instanceKlass.cpp	Wed Aug 08 15:24:21 2018 -0400
@@ -3665,7 +3665,7 @@
 // unloading only. Also resets the flag to false. purge_previous_version
 // will set the flag to true if there are any left, i.e., if there's any
 // work to do for next time. This is to avoid the expensive code cache
-// walk in CLDG::do_unloading().
+// walk in CLDG::clean_deallocate_lists().
 bool InstanceKlass::has_previous_versions_and_reset() {
   bool ret = _has_previous_versions;
   log_trace(redefine, class, iklass, purge)("Class unloading: has_previous_versions = %s",

--- a/src/hotspot/share/oops/instanceKlass.hpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/oops/instanceKlass.hpp	Wed Aug 08 15:24:21 2018 -0400
@@ -839,6 +839,7 @@
   }
 
   static bool has_previous_versions_and_reset();
+  static bool has_previous_versions() { return _has_previous_versions; }
 
   // JVMTI: Support for caching a class file before it is modified by an agent that can do retransformation
   void set_cached_class_file(JvmtiCachedClassFileData *data) {

--- a/src/hotspot/share/prims/jvmtiRedefineClasses.cpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/prims/jvmtiRedefineClasses.cpp	Wed Aug 08 15:24:21 2018 -0400
@@ -237,6 +237,9 @@
 #ifdef PRODUCT
   }
 #endif
+
+  // Clean up any metadata now unreferenced while MetadataOnStackMark is set.
+  ClassLoaderDataGraph::clean_deallocate_lists(false);
 }
 
 void VM_RedefineClasses::doit_epilogue() {

--- a/src/hotspot/share/runtime/safepoint.cpp	Wed Aug 08 15:11:11 2018 -0400
+++ b/src/hotspot/share/runtime/safepoint.cpp	Wed Aug 08 15:24:21 2018 -0400
@@ -23,7 +23,7 @@
  */
 
 #include "precompiled.hpp"
-#include "classfile/classLoaderData.hpp"
+#include "classfile/classLoaderData.inline.hpp"
 #include "classfile/stringTable.hpp"
 #include "classfile/symbolTable.hpp"
 #include "classfile/systemDictionary.hpp"
@@ -719,6 +719,7 @@
         post_safepoint_cleanup_task_event(&event, name);
       }
     }
+
     _subtasks.all_tasks_completed(_num_workers);
   }
 };
@@ -748,8 +749,18 @@
     cleanup.work(0);
   }
 
+  // Needs to be done single threaded by the VMThread.  This walks
+  // the thread stacks looking for references to metadata before
+  // deciding to remove it from the metaspaces.
+  if (ClassLoaderDataGraph::should_clean_metaspaces_and_reset()) {
+    const char* name = "cleanup live ClassLoaderData metaspaces";
+    TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
+    ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces();
+  }
+
   // Finish monitor deflation.
   ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
+
 }
 
 

--- a/test/hotspot/jtreg/runtime/RedefineTests/RedefineRunningMethods.java	Wed Aug 08 15:11:11 2018 -0400
+++ b/test/hotspot/jtreg/runtime/RedefineTests/RedefineRunningMethods.java	Wed Aug 08 15:24:21 2018 -0400
@@ -31,9 +31,8 @@
  *          java.instrument
  *          jdk.jartool/sun.tools.jar
  * @run main RedefineClassHelper
- * @run main/othervm/timeout=180 -javaagent:redefineagent.jar -Xlog:redefine+class+iklass+add=trace,redefine+class+iklass+purge=trace,all=trace:file=all.log RedefineRunningMethods
+ * @run main/othervm/timeout=180 -javaagent:redefineagent.jar -Xlog:redefine+class+iklass+add=trace,redefine+class+iklass+purge=trace,class+loader+data=debug,safepoint+cleanup,gc+phases=debug:rt.log RedefineRunningMethods
  */
-// Test is executed with full trace logging redirected to a file to ensure there is no crash during logging anonymous classes - see JDK-8197901
 
 
 // package access top-level class to avoid problem with RedefineClassHelper