--- a/hotspot/src/share/vm/gc_implementation/g1/heapRegionSet.cpp	Mon Mar 17 13:07:55 2014 +0100
+++ b/hotspot/src/share/vm/gc_implementation/g1/heapRegionSet.cpp	Mon Mar 17 13:42:16 2014 +0100
@@ -272,3 +272,108 @@
     }
   }
 }
+
+void FreeRegionList::verify_list() {
+  HeapRegion* curr = head();
+  HeapRegion* prev1 = NULL;
+  HeapRegion* prev0 = NULL;
+  uint count = 0;
+  size_t capacity = 0;
+  while (curr != NULL) {
+    verify_region(curr);
+
+    count++;
+    guarantee(count < _unrealistically_long_length,
+        hrs_err_msg("[%s] the calculated length: %u seems very long, is there maybe a cycle? curr: "PTR_FORMAT" prev0: "PTR_FORMAT" " "prev1: "PTR_FORMAT" length: %u", name(), count, curr, prev0, prev1, length()));
+
+    capacity += curr->capacity();
+
+    prev1 = prev0;
+    prev0 = curr;
+    curr = curr->next();
+  }
+
+  guarantee(tail() == prev0, err_msg("Expected %s to end with %u but it ended with %u.", name(), tail()->hrs_index(), prev0->hrs_index()));
+
+  guarantee(length() == count, err_msg("%s count mismatch. Expected %u, actual %u.", name(), length(), count));
+  guarantee(total_capacity_bytes() == capacity, err_msg("%s capacity mismatch. Expected " SIZE_FORMAT ", actual " SIZE_FORMAT,
+      name(), total_capacity_bytes(), capacity));
+}
+
+// Note on the check_mt_safety() methods below:
+//
+// Verification of the "master" heap region sets / lists that are
+// maintained by G1CollectedHeap is always done during a STW pause and
+// by the VM thread at the start / end of the pause. The standard
+// verification methods all assert check_mt_safety(). This is
+// important as it ensures that verification is done without
+// concurrent updates taking place at the same time. It follows, that,
+// for the "master" heap region sets / lists, the check_mt_safety()
+// method should include the VM thread / STW case.
+
+void MasterFreeRegionListMtSafeChecker::check() {
+  // Master Free List MT safety protocol:
+  // (a) If we're at a safepoint, operations on the master free list
+  // should be invoked by either the VM thread (which will serialize
+  // them) or by the GC workers while holding the
+  // FreeList_lock.
+  // (b) If we're not at a safepoint, operations on the master free
+  // list should be invoked while holding the Heap_lock.
+
+  if (SafepointSynchronize::is_at_safepoint()) {
+    guarantee(Thread::current()->is_VM_thread() ||
+              FreeList_lock->owned_by_self(), "master free list MT safety protocol at a safepoint");
+  } else {
+    guarantee(Heap_lock->owned_by_self(), "master free list MT safety protocol outside a safepoint");
+  }
+}
+
+void SecondaryFreeRegionListMtSafeChecker::check() {
+  // Secondary Free List MT safety protocol:
+  // Operations on the secondary free list should always be invoked
+  // while holding the SecondaryFreeList_lock.
+
+  guarantee(SecondaryFreeList_lock->owned_by_self(), "secondary free list MT safety protocol");
+}
+
+void OldRegionSetMtSafeChecker::check() {
+  // Master Old Set MT safety protocol:
+  // (a) If we're at a safepoint, operations on the master old set
+  // should be invoked:
+  // - by the VM thread (which will serialize them), or
+  // - by the GC workers while holding the FreeList_lock, if we're
+  //   at a safepoint for an evacuation pause (this lock is taken
+  //   anyway when an GC alloc region is retired so that a new one
+  //   is allocated from the free list), or
+  // - by the GC workers while holding the OldSets_lock, if we're at a
+  //   safepoint for a cleanup pause.
+  // (b) If we're not at a safepoint, operations on the master old set
+  // should be invoked while holding the Heap_lock.
+
+  if (SafepointSynchronize::is_at_safepoint()) {
+    guarantee(Thread::current()->is_VM_thread()
+        || FreeList_lock->owned_by_self() || OldSets_lock->owned_by_self(),
+        "master old set MT safety protocol at a safepoint");
+  } else {
+    guarantee(Heap_lock->owned_by_self(), "master old set MT safety protocol outside a safepoint");
+  }
+}
+
+void HumongousRegionSetMtSafeChecker::check() {
+  // Humongous Set MT safety protocol:
+  // (a) If we're at a safepoint, operations on the master humongous
+  // set should be invoked by either the VM thread (which will
+  // serialize them) or by the GC workers while holding the
+  // OldSets_lock.
+  // (b) If we're not at a safepoint, operations on the master
+  // humongous set should be invoked while holding the Heap_lock.
+
+  if (SafepointSynchronize::is_at_safepoint()) {
+    guarantee(Thread::current()->is_VM_thread() ||
+              OldSets_lock->owned_by_self(),
+              "master humongous set MT safety protocol at a safepoint");
+  } else {
+    guarantee(Heap_lock->owned_by_self(),
+              "master humongous set MT safety protocol outside a safepoint");
+  }
+}