From a669d665b72689dcabb60805c92507776ed4aef9 Mon Sep 17 00:00:00 2001
From: johnc <unknown>
Date: Tue, 7 Dec 2010 16:18:45 -0800
Subject: [PATCH] 6994628: G1: Test gc/gctests/FinalizeTest05 fails (one live
 object is finalized) Summary: The Solaris Studio 12 update 1 C++ compiler was
 incorrectly re-ordering the reads of an object's mark word in
 oopDesc::forward_to_atomic(). This opened a small window where one thread
 could execute the successful CAS path even though another thread had already
 successfully forwarded the object. This could result in an object being
 copied twice. The code in oopDesc::forward_to_atomic() was changed to read
 the mark word once. Reviewed-by: ysr, tonyp

---
 src/share/vm/oops/oop.pcgc.inline.hpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/share/vm/oops/oop.pcgc.inline.hpp b/src/share/vm/oops/oop.pcgc.inline.hpp
index 22f290f43..fc969970c 100644
--- a/src/share/vm/oops/oop.pcgc.inline.hpp
+++ b/src/share/vm/oops/oop.pcgc.inline.hpp
@@ -118,12 +118,15 @@ inline oop oopDesc::forward_to_atomic(oop p) {
   assert(forwardPtrMark->decode_pointer() == p, "encoding must be reversable");
   assert(sizeof(markOop) == sizeof(intptr_t), "CAS below requires this.");
 
-  while (!is_forwarded()) {
+  while (!oldMark->is_marked()) {
     curMark = (markOop)Atomic::cmpxchg_ptr(forwardPtrMark, &_mark, oldMark);
+    assert(is_forwarded(), "object should have been forwarded");
     if (curMark == oldMark) {
-      assert(is_forwarded(), "the CAS should have succeeded.");
       return NULL;
     }
+    // If the CAS was unsuccessful then curMark->is_marked()
+    // should return true as another thread has CAS'd in another
+    // forwarding pointer.
     oldMark = curMark;
   }
   return forwardee();
-- 
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