--- a/hotspot/src/share/vm/gc/g1/g1CodeCacheRemSet.cpp	Thu Jan 28 16:34:44 2016 +0100
+++ b/hotspot/src/share/vm/gc/g1/g1CodeCacheRemSet.cpp	Thu Jan 28 19:30:39 2016 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2016, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -74,10 +74,16 @@
   static size_t static_mem_size() {
     return sizeof(_purge_list);
   }
+
+  size_t mem_size();
 };
 
 CodeRootSetTable* volatile CodeRootSetTable::_purge_list = NULL;
 
+size_t CodeRootSetTable::mem_size() {
+  return sizeof(CodeRootSetTable) + (entry_size() * number_of_entries()) + (sizeof(HashtableBucket<mtGC>) * table_size());
+}
+
 CodeRootSetTable::Entry* CodeRootSetTable::new_entry(nmethod* nm) {
   unsigned int hash = compute_hash(nm);
   Entry* entry = (Entry*) new_entry_free_list();
@@ -232,7 +238,6 @@
   OrderAccess::release_store_ptr(&_table, temp);
 }
 
-
 void G1CodeRootSet::purge() {
   CodeRootSetTable::purge();
 }
@@ -247,12 +252,13 @@
     allocate_small_table();
   }
   added = _table->add(method);
-  if (_length == Threshold) {
-    move_to_large();
-  }
   if (added) {
+    if (_length == Threshold) {
+      move_to_large();
+    }
     ++_length;
   }
+  assert(_length == (size_t)_table->number_of_entries(), "sizes should match");
 }
 
 bool G1CodeRootSet::remove(nmethod* method) {
@@ -266,11 +272,13 @@
       clear();
     }
   }
+  assert((_length == 0 && _table == NULL) ||
+         (_length == (size_t)_table->number_of_entries()), "sizes should match");
   return removed;
 }
 
 bool G1CodeRootSet::contains(nmethod* method) {
-  CodeRootSetTable* table = load_acquire_table();
+  CodeRootSetTable* table = load_acquire_table(); // contains() may be called outside of lock, so ensure mem sync.
   if (table != NULL) {
     return table->contains(method);
   }
@@ -284,8 +292,7 @@
 }
 
 size_t G1CodeRootSet::mem_size() {
-  return sizeof(*this) +
-      (_table != NULL ? sizeof(CodeRootSetTable) + _table->entry_size() * _length : 0);
+  return sizeof(*this) + (_table != NULL ? _table->mem_size() : 0);
 }
 
 void G1CodeRootSet::nmethods_do(CodeBlobClosure* blk) const {

--- a/hotspot/src/share/vm/gc/g1/heapRegionRemSet.cpp	Thu Jan 28 16:34:44 2016 +0100
+++ b/hotspot/src/share/vm/gc/g1/heapRegionRemSet.cpp	Thu Jan 28 19:30:39 2016 +0100
@@ -789,6 +789,9 @@
 
 void HeapRegionRemSet::add_strong_code_root(nmethod* nm) {
   assert(nm != NULL, "sanity");
+  assert((!CodeCache_lock->owned_by_self() || SafepointSynchronize::is_at_safepoint()),
+          "should call add_strong_code_root_locked instead. CodeCache_lock->owned_by_self(): %s, is_at_safepoint(): %s",
+          BOOL_TO_STR(CodeCache_lock->owned_by_self()), BOOL_TO_STR(SafepointSynchronize::is_at_safepoint()));
   // Optimistic unlocked contains-check
   if (!_code_roots.contains(nm)) {
     MutexLockerEx ml(&_m, Mutex::_no_safepoint_check_flag);
@@ -798,6 +801,12 @@
 
 void HeapRegionRemSet::add_strong_code_root_locked(nmethod* nm) {
   assert(nm != NULL, "sanity");
+  assert((CodeCache_lock->owned_by_self() ||
+         (SafepointSynchronize::is_at_safepoint() &&
+          (_m.owned_by_self() || Thread::current()->is_VM_thread()))),
+          "not safely locked. CodeCache_lock->owned_by_self(): %s, is_at_safepoint(): %s, _m.owned_by_self(): %s, Thread::current()->is_VM_thread(): %s",
+          BOOL_TO_STR(CodeCache_lock->owned_by_self()), BOOL_TO_STR(SafepointSynchronize::is_at_safepoint()),
+          BOOL_TO_STR(_m.owned_by_self()), BOOL_TO_STR(Thread::current()->is_VM_thread()));
   _code_roots.add(nm);
 }