8251945: SIGSEGV in PackageEntry::purge_qualified_exports()

Reviewed-by: adinn

src/hotspot/share/classfile/classLoaderData.cpp

@@ -1,5 +1,5 @@
  /*
- * Copyright (c) 2012, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2021, 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
@@ -1041,22 +1041,24 @@ bool ClassLoaderDataGraph::_metaspace_oom = false;
 // Add a new class loader data node to the list.  Assign the newly created
 // ClassLoaderData into the java/lang/ClassLoader object as a hidden field
 ClassLoaderData* ClassLoaderDataGraph::add_to_graph(Handle loader, bool is_anonymous) {
-  NoSafepointVerifier no_safepoints; // we mustn't GC until we've installed the
-                                     // ClassLoaderData in the graph since the CLD
-                                     // contains oops in _handles that must be walked.
-
-  ClassLoaderData* cld = new ClassLoaderData(loader, is_anonymous);
+  ClassLoaderData* cld;
 
   if (!is_anonymous) {
-    // First, Atomically set it
-    ClassLoaderData* old = java_lang_ClassLoader::cmpxchg_loader_data(cld, loader(), NULL);
-    if (old != NULL) {
-      delete cld;
-      // Returns the data.
-      return old;
+    MutexLocker ml(ClassLoaderDataGraph_lock);
+    cld = java_lang_ClassLoader::loader_data_raw(loader());
+    if (cld != NULL) {
+      return cld;
     }
+    cld = new ClassLoaderData(loader, is_anonymous);
+    java_lang_ClassLoader::release_set_loader_data(loader(), cld);
+  } else {
+    cld = new ClassLoaderData(loader, is_anonymous);
   }
 
+  NoSafepointVerifier no_safepoints; // we mustn't GC until we've installed the
+                                     // ClassLoaderData in the graph since the CLD
+                                     // contains oops in _handles that must be walked.
+
   // We won the race, and therefore the task of adding the data to the list of
   // class loader data
   ClassLoaderData** list_head = &_head;

src/hotspot/share/classfile/classLoaderData.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2021, 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
@@ -45,7 +45,7 @@ inline ClassLoaderData* ClassLoaderData::class_loader_data_or_null(oop loader) {
   if (loader == NULL) {
     return ClassLoaderData::the_null_class_loader_data();
   }
-  return java_lang_ClassLoader::loader_data(loader);
+  return java_lang_ClassLoader::loader_data_acquire(loader);
 }
 
 inline ClassLoaderData* ClassLoaderData::class_loader_data(oop loader) {
@@ -59,7 +59,7 @@ inline ClassLoaderData *ClassLoaderDataGraph::find_or_create(Handle loader) {
   guarantee(loader() != NULL && oopDesc::is_oop(loader()), "Loader must be oop");
   // Gets the class loader data out of the java/lang/ClassLoader object, if non-null
   // it's already in the loader_data, so no need to add
-  ClassLoaderData* loader_data= java_lang_ClassLoader::loader_data(loader());
+  ClassLoaderData* loader_data= java_lang_ClassLoader::loader_data_acquire(loader());
   if (loader_data) {
      return loader_data;
   }

src/hotspot/share/classfile/classLoaderStats.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2021, 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
@@ -139,7 +139,7 @@ void ClassLoaderStatsClosure::print() {
 
 
 void ClassLoaderStatsClosure::addEmptyParents(oop cl) {
-  while (cl != NULL && java_lang_ClassLoader::loader_data(cl) == NULL) {
+  while (cl != NULL && java_lang_ClassLoader::loader_data_acquire(cl) == NULL) {
     // This classloader has not loaded any classes
     ClassLoaderStats** cls_ptr = _stats->get(cl);
     if (cls_ptr == NULL) {

src/hotspot/share/classfile/javaClasses.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2021, 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
@@ -4020,14 +4020,20 @@ int  java_lang_ClassLoader::name_offset = -1;
 int  java_lang_ClassLoader::nameAndId_offset = -1;
 int  java_lang_ClassLoader::unnamedModule_offset = -1;
 
-ClassLoaderData* java_lang_ClassLoader::loader_data(oop loader) {
+ClassLoaderData* java_lang_ClassLoader::loader_data_acquire(oop loader) {
   assert(loader != NULL && oopDesc::is_oop(loader), "loader must be oop");
-  return HeapAccess<>::load_at(loader, _loader_data_offset);
+  return HeapAccess<MO_ACQUIRE>::load_at(loader, _loader_data_offset);
 }
 
-ClassLoaderData* java_lang_ClassLoader::cmpxchg_loader_data(ClassLoaderData* new_data, oop loader, ClassLoaderData* expected_data) {
+ClassLoaderData* java_lang_ClassLoader::loader_data_raw(oop loader) {
   assert(loader != NULL && oopDesc::is_oop(loader), "loader must be oop");
-  return HeapAccess<>::atomic_cmpxchg_at(new_data, loader, _loader_data_offset, expected_data);
+  return RawAccess<>::load_at(loader, _loader_data_offset);
+}
+
+void java_lang_ClassLoader::release_set_loader_data(oop loader, ClassLoaderData* new_data) {
+  assert(loader != NULL, "loader must not be NULL");
+  assert(oopDesc::is_oop(loader), "loader must be oop");
+  HeapAccess<MO_RELEASE>::store_at(loader, _loader_data_offset, new_data);
 }
 
 #define CLASSLOADER_FIELDS_DO(macro) \

src/hotspot/share/classfile/javaClasses.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2021, 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
@@ -1320,8 +1320,9 @@ class java_lang_ClassLoader : AllStatic {
   static void compute_offsets();
   static void serialize_offsets(SerializeClosure* f) NOT_CDS_RETURN;
 
-  static ClassLoaderData* loader_data(oop loader);
-  static ClassLoaderData* cmpxchg_loader_data(ClassLoaderData* new_data, oop loader, ClassLoaderData* expected_data);
+  static ClassLoaderData* loader_data_acquire(oop loader);
+  static ClassLoaderData* loader_data_raw(oop loader);
+  static void release_set_loader_data(oop loader, ClassLoaderData* new_data);
 
   static oop parent(oop loader);
   static oop name(oop loader);

src/hotspot/share/gc/parallel/psCompactionManager.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2021, 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
@@ -183,7 +183,7 @@ void InstanceMirrorKlass::oop_pc_follow_contents(oop obj, ParCompactionManager*
 void InstanceClassLoaderKlass::oop_pc_follow_contents(oop obj, ParCompactionManager* cm) {
   InstanceKlass::oop_pc_follow_contents(obj, cm);
 
-  ClassLoaderData * const loader_data = java_lang_ClassLoader::loader_data(obj);
+  ClassLoaderData * const loader_data = java_lang_ClassLoader::loader_data_acquire(obj);
   if (loader_data != NULL) {
     cm->follow_class_loader(loader_data);
   }

src/hotspot/share/jfr/periodic/jfrPeriodic.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2021, 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
@@ -468,9 +468,9 @@ class JfrClassLoaderStatsClosure : public ClassLoaderStatsClosure {
 
   bool do_entry(oop const& key, ClassLoaderStats* const& cls) {
     const ClassLoaderData* this_cld = cls->_class_loader != NULL ?
-      java_lang_ClassLoader::loader_data(cls->_class_loader) : (ClassLoaderData*)NULL;
+      java_lang_ClassLoader::loader_data_acquire(cls->_class_loader) : (ClassLoaderData*)NULL;
     const ClassLoaderData* parent_cld = cls->_parent != NULL ?
-      java_lang_ClassLoader::loader_data(cls->_parent) : (ClassLoaderData*)NULL;
+      java_lang_ClassLoader::loader_data_acquire(cls->_parent) : (ClassLoaderData*)NULL;
     EventClassLoaderStatistics event;
     event.set_classLoader(this_cld);
     event.set_parentClassLoader(parent_cld);

src/hotspot/share/oops/instanceClassLoaderKlass.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2021, 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
@@ -39,7 +39,7 @@ inline void InstanceClassLoaderKlass::oop_oop_iterate(oop obj, OopClosureType* c
   InstanceKlass::oop_oop_iterate<T>(obj, closure);
 
   if (Devirtualizer::do_metadata(closure)) {
-    ClassLoaderData* cld = java_lang_ClassLoader::loader_data(obj);
+    ClassLoaderData* cld = java_lang_ClassLoader::loader_data_acquire(obj);
     // cld can be null if we have a non-registered class loader.
     if (cld != NULL) {
       Devirtualizer::do_cld(closure, cld);
@@ -61,7 +61,7 @@ inline void InstanceClassLoaderKlass::oop_oop_iterate_bounded(oop obj, OopClosur
 
   if (Devirtualizer::do_metadata(closure)) {
     if (mr.contains(obj)) {
-      ClassLoaderData* cld = java_lang_ClassLoader::loader_data(obj);
+      ClassLoaderData* cld = java_lang_ClassLoader::loader_data_acquire(obj);
       // cld can be null if we have a non-registered class loader.
       if (cld != NULL) {
         Devirtualizer::do_cld(closure, cld);

src/hotspot/share/prims/whitebox.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2021, 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
@@ -1550,7 +1550,7 @@ WB_ENTRY(jlong, WB_AllocateMetaspace(JNIEnv* env, jobject wb, jobject class_load
 
   oop class_loader_oop = JNIHandles::resolve(class_loader);
   ClassLoaderData* cld = class_loader_oop != NULL
-      ? java_lang_ClassLoader::loader_data(class_loader_oop)
+      ? java_lang_ClassLoader::loader_data_acquire(class_loader_oop)
       : ClassLoaderData::the_null_class_loader_data();
 
   void* metadata = MetadataFactory::new_array<u1>(cld, WhiteBox::array_bytes_to_length((size_t)size), thread);
@@ -1561,7 +1561,7 @@ WB_END
 WB_ENTRY(void, WB_FreeMetaspace(JNIEnv* env, jobject wb, jobject class_loader, jlong addr, jlong size))
   oop class_loader_oop = JNIHandles::resolve(class_loader);
   ClassLoaderData* cld = class_loader_oop != NULL
-      ? java_lang_ClassLoader::loader_data(class_loader_oop)
+      ? java_lang_ClassLoader::loader_data_acquire(class_loader_oop)
       : ClassLoaderData::the_null_class_loader_data();
 
   MetadataFactory::free_array(cld, (Array<u1>*)(uintptr_t)addr);

src/hotspot/share/runtime/mutexLocker.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2021, 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
@@ -148,6 +148,7 @@ Mutex*   UnsafeJlong_lock             = NULL;
 Monitor* CodeHeapStateAnalytics_lock  = NULL;
 
 Mutex*   MetaspaceExpand_lock         = NULL;
+Mutex*   ClassLoaderDataGraph_lock    = NULL;
 Mutex*   ThreadIdTableCreate_lock     = NULL;
 Monitor* ThreadsSMRDelete_lock       = NULL;
 Mutex*   SharedDecoder_lock           = NULL;
@@ -239,6 +240,7 @@ void mutex_init() {
   def(OopMapCacheAlloc_lock        , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_always);     // used for oop_map_cache allocation.
 
   def(MetaspaceExpand_lock         , PaddedMutex  , leaf-1,      true,  Monitor::_safepoint_check_never);
+  def(ClassLoaderDataGraph_lock    , PaddedMutex  , nonleaf,     true,  Monitor::_safepoint_check_always);
 
   def(Patching_lock                , PaddedMutex  , special,     true,  Monitor::_safepoint_check_never);      // used for safepointing and code patching.
   def(Service_lock                 , PaddedMonitor, special,     true,  Monitor::_safepoint_check_never);      // used for service thread operations

src/hotspot/share/runtime/mutexLocker.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2021, 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
@@ -151,7 +151,7 @@ extern Mutex*   UnsafeJlong_lock;                // provides Unsafe atomic updat
 #endif
 
 extern Mutex*   MetaspaceExpand_lock;            // protects Metaspace virtualspace and chunk expansions
-
+extern Mutex*   ClassLoaderDataGraph_lock;       // protects CLDG list, needed for concurrent unloading
 
 extern Monitor* CodeHeapStateAnalytics_lock;     // lock print functions against concurrent analyze functions.
                                                  // Only used locally in PrintCodeCacheLayout processing.