HADOOP-3520. TestDFSUpgradeFromImage triggers a race condition in the

Upgrade Manager. Fixed. (dhruba)
svn merge -c 669258 from trunk



git-svn-id: https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.18@669260 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -611,6 +611,9 @@ Release 0.18.0 - Unreleased
     HADOOP-3539.  Fix the tool path in the bin/hadoop script under
     cygwin. (Tsz Wo (Nicholas), Sze via omalley)
 
+    HADOOP-3520.  TestDFSUpgradeFromImage triggers a race condition in the
+    Upgrade Manager. Fixed. (dhruba)
+
 Release 0.17.1 - Unreleased
 
   INCOMPATIBLE CHANGES

src/hdfs/org/apache/hadoop/dfs/UpgradeManagerDatanode.java

@@ -18,7 +18,6 @@
 package org.apache.hadoop.dfs;
 
 import java.io.IOException;
-import java.net.SocketTimeoutException;
 
 import org.apache.hadoop.util.Daemon;
 
@@ -44,7 +43,7 @@ class UpgradeManagerDatanode extends UpgradeManager {
     return FSConstants.NodeType.DATA_NODE;
   }
 
-  void initializeUpgrade(NamespaceInfo nsInfo) throws IOException {
+  synchronized void initializeUpgrade(NamespaceInfo nsInfo) throws IOException {
     if( ! super.initializeUpgrade())
       return; // distr upgrade is not needed
     DataNode.LOG.info("\n   Distributed upgrade for DataNode "