From db54008b5f4bbf19f1a3a5dd93e33ec03ef28f56 Mon Sep 17 00:00:00 2001
From: jiefu <none@none>
Date: Wed, 7 Aug 2019 17:00:19 +0800
Subject: [PATCH] 8229169: False failure of GenericTaskQueue::pop_local on
 architectures with weak memory model Reviewed-by: mdoerr, kbarrett, tschatzl

---
 src/share/vm/utilities/taskqueue.hpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/share/vm/utilities/taskqueue.hpp b/src/share/vm/utilities/taskqueue.hpp
index d2b39c943..0a2af4cdb 100644
--- a/src/share/vm/utilities/taskqueue.hpp
+++ b/src/share/vm/utilities/taskqueue.hpp
@@ -714,6 +714,11 @@ GenericTaskQueue<E, F, N>::pop_local(volatile E& t) {
   } else {
     // Otherwise, the queue contained exactly one element; we take the slow
     // path.
+
+    // The barrier is required to prevent reordering the two reads of _age:
+    // one is the _age.get() below, and the other is _age.top() above the if-stmt.
+    // The algorithm may fail if _age.get() reads an older value than _age.top().
+    OrderAccess::loadload();
     return pop_local_slow(localBot, _age.get());
   }
 }
-- 
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