8223177: Data race on JvmtiEnvBase::_tag_map in double-checked locking

Summary: Add memory fences on accesses to JvmtiEnvBase::_tag_map
Reviewed-by: dholmes, jcbeyler, sspitsyn

src/share/vm/prims/jvmtiEnvBase.hpp

@@ -32,6 +32,7 @@
 #include "runtime/fieldDescriptor.hpp"
 #include "runtime/frame.hpp"
 #include "runtime/handles.inline.hpp"
+#include "runtime/orderAccess.hpp"
 #include "runtime/thread.hpp"
 #include "runtime/vm_operations.hpp"
 #include "utilities/growableArray.hpp"
@@ -97,7 +98,7 @@ class JvmtiEnvBase : public CHeapObj<mtInternal> {
   const void *_env_local_storage;     // per env agent allocated data.
   jvmtiEventCallbacks _event_callbacks;
   jvmtiExtEventCallbacks _ext_event_callbacks;
-  JvmtiTagMap* _tag_map;
+  JvmtiTagMap* volatile _tag_map;
   JvmtiEnvEventEnable _env_event_enable;
   jvmtiCapabilities _current_capabilities;
   jvmtiCapabilities _prohibited_capabilities;
@@ -251,6 +252,13 @@ class JvmtiEnvBase : public CHeapObj<mtInternal> {
     return _tag_map;
   }
 
+  JvmtiTagMap* acquire_tag_map() {
+    return (JvmtiTagMap*)OrderAccess::load_ptr_acquire(&_tag_map);
+  }
+
+  void release_set_tag_map(JvmtiTagMap* tag_map) {
+    OrderAccess::release_store_ptr(&_tag_map, tag_map);
+  }
 
   // return true if event is enabled globally or for any thread
   // True only if there is a callback for it.

src/share/vm/prims/jvmtiTagMap.cpp

@@ -430,7 +430,7 @@ JvmtiTagMap::JvmtiTagMap(JvmtiEnv* env) :
   _hashmap = new JvmtiTagHashmap();
 
   // finally add us to the environment
-  ((JvmtiEnvBase *)env)->set_tag_map(this);
+  ((JvmtiEnvBase *)env)->release_set_tag_map(this);
 }
 
 
@@ -499,7 +499,7 @@ void JvmtiTagMap::destroy_entry(JvmtiTagHashmapEntry* entry) {
 // returns the tag map for the given environments. If the tag map
 // doesn't exist then it is created.
 JvmtiTagMap* JvmtiTagMap::tag_map_for(JvmtiEnv* env) {
-  JvmtiTagMap* tag_map = ((JvmtiEnvBase*)env)->tag_map();
+  JvmtiTagMap* tag_map = ((JvmtiEnvBase*)env)->acquire_tag_map();
   if (tag_map == NULL) {
     MutexLocker mu(JvmtiThreadState_lock);
     tag_map = ((JvmtiEnvBase*)env)->tag_map();
@@ -3282,7 +3282,7 @@ void JvmtiTagMap::weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f) {
   if (JvmtiEnv::environments_might_exist()) {
     JvmtiEnvIterator it;
     for (JvmtiEnvBase* env = it.first(); env != NULL; env = it.next(env)) {
-      JvmtiTagMap* tag_map = env->tag_map();
+      JvmtiTagMap* tag_map = env->acquire_tag_map();
       if (tag_map != NULL && !tag_map->is_empty()) {
         tag_map->do_weak_oops(is_alive, f);
       }