--- a/src/share/vm/services/memBaseline.cpp	Wed Apr 24 09:00:04 2013 -0400
+++ b/src/share/vm/services/memBaseline.cpp	Wed Apr 24 14:55:04 2013 -0400
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2013, 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
@@ -23,9 +23,12 @@
  */
 #include "precompiled.hpp"
 #include "memory/allocation.hpp"
+#include "runtime/safepoint.hpp"
+#include "runtime/thread.inline.hpp"
 #include "services/memBaseline.hpp"
 #include "services/memTracker.hpp"
 
+
 MemType2Name MemBaseline::MemType2NameMap[NUMBER_OF_MEMORY_TYPE] = {
   {mtJavaHeap,   "Java Heap"},
   {mtClass,      "Class"},
@@ -149,6 +152,14 @@
   return true;
 }
 
+// check if there is a safepoint in progress, if so, block the thread
+// for the safepoint
+void MemBaseline::check_safepoint(JavaThread* thr) {
+  if (SafepointSynchronize::is_synchronizing()) {
+    SafepointSynchronize::block(thr);
+  }
+}
+
 // baseline mmap'd memory records, generate overall summary and summaries by
 // memory types
 bool MemBaseline::baseline_vm_summary(const MemPointerArray* vm_records) {
@@ -306,7 +317,7 @@
         committed_rec->pc() != vm_ptr->pc()) {
         if (!_vm_map->append(vm_ptr)) {
           return false;
-  }
+        }
         committed_rec = (VMMemRegionEx*)_vm_map->at(_vm_map->length() - 1);
     } else {
         committed_rec->expand_region(vm_ptr->addr(), vm_ptr->size());
@@ -344,16 +355,27 @@
 
 // baseline a snapshot. If summary_only = false, memory usages aggregated by
 // callsites are also baselined.
+// The method call can be lengthy, especially when detail tracking info is
+// requested. So the method checks for safepoint explicitly.
 bool MemBaseline::baseline(MemSnapshot& snapshot, bool summary_only) {
-  MutexLockerEx snapshot_locker(snapshot._lock, true);
+  Thread* THREAD = Thread::current();
+  assert(THREAD->is_Java_thread(), "must be a JavaThread");
+  MutexLocker snapshot_locker(snapshot._lock);
   reset();
-  _baselined = baseline_malloc_summary(snapshot._alloc_ptrs) &&
-               baseline_vm_summary(snapshot._vm_ptrs);
+  _baselined = baseline_malloc_summary(snapshot._alloc_ptrs);
+  if (_baselined) {
+    check_safepoint((JavaThread*)THREAD);
+    _baselined = baseline_vm_summary(snapshot._vm_ptrs);
+  }
   _number_of_classes = snapshot.number_of_classes();
 
   if (!summary_only && MemTracker::track_callsite() && _baselined) {
-    _baselined =  baseline_malloc_details(snapshot._alloc_ptrs) &&
-      baseline_vm_details(snapshot._vm_ptrs);
+    check_safepoint((JavaThread*)THREAD);
+    _baselined =  baseline_malloc_details(snapshot._alloc_ptrs);
+    if (_baselined) {
+      check_safepoint((JavaThread*)THREAD);
+      _baselined =  baseline_vm_details(snapshot._vm_ptrs);
+    }
   }
   return _baselined;
 }

--- a/src/share/vm/services/memBaseline.hpp	Wed Apr 24 09:00:04 2013 -0400
+++ b/src/share/vm/services/memBaseline.hpp	Wed Apr 24 14:55:04 2013 -0400
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2013, 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
@@ -330,6 +330,9 @@
   // should not use copy constructor
   MemBaseline(MemBaseline& copy) { ShouldNotReachHere(); }
 
+  // check and block at a safepoint
+  static inline void check_safepoint(JavaThread* thr);
+
  public:
   // create a memory baseline
   MemBaseline();

--- a/src/share/vm/services/memTracker.cpp	Wed Apr 24 09:00:04 2013 -0400
+++ b/src/share/vm/services/memTracker.cpp	Wed Apr 24 14:55:04 2013 -0400
@@ -573,7 +573,7 @@
 
 // baseline current memory snapshot
 bool MemTracker::baseline() {
-  MutexLockerEx lock(_query_lock, true);
+  MutexLocker lock(_query_lock);
   MemSnapshot* snapshot = get_snapshot();
   if (snapshot != NULL) {
     return _baseline.baseline(*snapshot, false);
@@ -584,7 +584,7 @@
 // print memory usage from current snapshot
 bool MemTracker::print_memory_usage(BaselineOutputer& out, size_t unit, bool summary_only) {
   MemBaseline  baseline;
-  MutexLockerEx lock(_query_lock, true);
+  MutexLocker  lock(_query_lock);
   MemSnapshot* snapshot = get_snapshot();
   if (snapshot != NULL && baseline.baseline(*snapshot, summary_only)) {
     BaselineReporter reporter(out, unit);
@@ -597,7 +597,7 @@
 // Whitebox API for blocking until the current generation of NMT data has been merged
 bool MemTracker::wbtest_wait_for_data_merge() {
   // NMT can't be shutdown while we're holding _query_lock
-  MutexLockerEx lock(_query_lock, true);
+  MutexLocker lock(_query_lock);
   assert(_worker_thread != NULL, "Invalid query");
   // the generation at query time, so NMT will spin till this generation is processed
   unsigned long generation_at_query_time = SequenceGenerator::current_generation();
@@ -641,7 +641,7 @@
 
 // compare memory usage between current snapshot and baseline
 bool MemTracker::compare_memory_usage(BaselineOutputer& out, size_t unit, bool summary_only) {
-  MutexLockerEx lock(_query_lock, true);
+  MutexLocker lock(_query_lock);
   if (_baseline.baselined()) {
     MemBaseline baseline;
     MemSnapshot* snapshot = get_snapshot();