Fix weak consistency bug in cpumgr.

Change-Id: Ie0ba82a759afee2e4809924b32c7ef0fefcd0ad1
Reviewed-on: http://gfw160.austin.ibm.com:8080/gerrit/914
Tested-by: Jenkins Server
Reviewed-by: Douglas R. Gilbert <dgilbert@us.ibm.com>
Reviewed-by: Daniel M. Crowell <dcrowell@us.ibm.com>
Reviewed-by: A. Patrick Williams III <iawillia@us.ibm.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/src/kernel/cpumgr.C b/src/kernel/cpumgr.C
index eb1ad3ac2..33290ebf1 100644
--- a/src/kernel/cpumgr.C
+++ b/src/kernel/cpumgr.C
@@ -212,12 +212,14 @@ void CpuManager::executePeriodics(cpu_t * i_cpu)
         {
             // set up barrier based on # cpus cv_barrier;
             // TODO whatif other cpus become active?
-            isync();
-            cv_barrier.init(cv_cpuCount);
+            isync(); // Ensure all instructions complete before this point, so
+                     // we don't get a stale shutdown_requested.
             if(!cv_shutdown_requested)
             {
+                cv_barrier.init(cv_cpuCount);
+                lwsync();  // Ensure barrier init is globally visible before
+                           // setting defrag = true.
                 cv_defrag = true;
-                lwsync();
             }
         }
     }