diff -r 8ff882030755 src/share/vm/runtime/thread.cpp
--- a/src/share/vm/runtime/thread.cpp	Wed Jan 28 16:45:35 2015 -0800
+++ b/src/share/vm/runtime/thread.cpp	Tue Feb 03 13:52:32 2015 -0500
@@ -1318,24 +1318,20 @@
 }
 
 void WatcherThread::stop() {
-  // Get the PeriodicTask_lock if we can. If we cannot, then the
-  // WatcherThread is using it and we don't want to block on that lock
-  // here because that might cause a safepoint deadlock depending on
-  // what the current WatcherThread tasks are doing.
-  bool have_lock = PeriodicTask_lock->try_lock();
-
   _should_terminate = true;
-  OrderAccess::fence();  // ensure WatcherThread sees update in main loop
-
-  if (have_lock) {
+  {
+    // Let safepoints happen to avoid the deadlock:
+    // The VM thread has Threads_lock and waits for Java threads to report back for a safepoint.
+    // The watcher thread has PeriodicTask_lock and tries to acquire Threads_lock.
+    // A Java thread executes WatcherThread::stop, tries to acquire PeriodicTask_lock,
+    // and holds up the VM thread by not reaching a safepoint.
+    MutexLocker mu(PeriodicTask_lock);
+
     WatcherThread* watcher = watcher_thread();
     if (watcher != NULL) {
-      // If we managed to get the lock, then we should unpark the
-      // WatcherThread so that it can see we want it to stop.
+      // Unpark the WatcherThread so that it can see that it should terminate.
       watcher->unpark();
     }
-
-    PeriodicTask_lock->unlock();
   }
 
   // it is ok to take late safepoints here, if needed