8267842: SIGSEGV in get_current_contended_monitor

Reviewed-by: stefank, dcubed, ysuenaga, dholmes

Author: TheRealMDoerr

src/hotspot/share/runtime/thread.hpp

@@ -746,18 +746,21 @@ class JavaThread: public Thread {
   // elided card-marks for performance along the fast-path.
   MemRegion     _deferred_card_mark;
 
-  ObjectMonitor* _current_pending_monitor;              // ObjectMonitor this thread is waiting to lock
+  ObjectMonitor* volatile _current_pending_monitor;     // ObjectMonitor this thread is waiting to lock
   bool           _current_pending_monitor_is_from_java; // locking is from Java code
-  ObjectMonitor* _current_waiting_monitor;              // ObjectMonitor on which this thread called Object.wait()
+  ObjectMonitor* volatile _current_waiting_monitor;     // ObjectMonitor on which this thread called Object.wait()
  public:
   volatile intptr_t _Stalled;
 
   // For tracking the heavyweight monitor the thread is pending on.
   ObjectMonitor* current_pending_monitor() {
-    return _current_pending_monitor;
+    // Use Atomic::load() to prevent data race between concurrent modification and
+    // concurrent readers, e.g. ThreadService::get_current_contended_monitor().
+    // Especially, reloading pointer from thread after NULL check must be prevented.
+    return Atomic::load(&_current_pending_monitor);
   }
   void set_current_pending_monitor(ObjectMonitor* monitor) {
-    _current_pending_monitor = monitor;
+    Atomic::store(&_current_pending_monitor, monitor);
   }
   void set_current_pending_monitor_is_from_java(bool from_java) {
     _current_pending_monitor_is_from_java = from_java;
@@ -766,10 +769,11 @@ class JavaThread: public Thread {
     return _current_pending_monitor_is_from_java;
   }
   ObjectMonitor* current_waiting_monitor() {
-    return _current_waiting_monitor;
+    // See the comment in current_pending_monitor() above.
+    return Atomic::load(&_current_waiting_monitor);
   }
   void set_current_waiting_monitor(ObjectMonitor* monitor) {
-    _current_waiting_monitor = monitor;
+    Atomic::store(&_current_waiting_monitor, monitor);
   }
 
  private:

src/hotspot/share/runtime/vmStructs.cpp

@@ -740,9 +740,9 @@ typedef HashtableEntry<InstanceKlass*, mtClass>  KlassHashtableEntry;
   nonstatic_field(JavaThread,                  _anchor,                                       JavaFrameAnchor)                       \
   nonstatic_field(JavaThread,                  _vm_result,                                    oop)                                   \
   nonstatic_field(JavaThread,                  _vm_result_2,                                  Metadata*)                             \
-  nonstatic_field(JavaThread,                  _current_pending_monitor,                      ObjectMonitor*)                        \
+  volatile_nonstatic_field(JavaThread,         _current_pending_monitor,                      ObjectMonitor*)                        \
   nonstatic_field(JavaThread,                  _current_pending_monitor_is_from_java,         bool)                                  \
-  nonstatic_field(JavaThread,                  _current_waiting_monitor,                      ObjectMonitor*)                        \
+  volatile_nonstatic_field(JavaThread,         _current_waiting_monitor,                      ObjectMonitor*)                        \
   volatile_nonstatic_field(JavaThread,         _suspend_flags,                                uint32_t)                              \
   nonstatic_field(JavaThread,                  _async_exception_condition,                    JavaThread::AsyncExceptionCondition)   \
   nonstatic_field(JavaThread,                  _pending_async_exception,                      oop)                                   \