From 9e355719653c5e7b48b601090634882e4f29a743 Mon Sep 17 00:00:00 2001
From: Kihwal Lee <kihwal@apache.org>
Date: Fri, 19 Sep 2014 17:07:06 -0500
Subject: [PATCH] HDFS-7046. HA NN can NPE upon transition to active.
 Contributed by Kihwal Lee.

---
 hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt                 | 2 ++
 .../apache/hadoop/hdfs/server/namenode/FSNamesystem.java    | 6 +++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 9d4d8edf129..8c45d699c08 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -782,6 +782,8 @@ Release 2.6.0 - UNRELEASED
     HDFS-7096. Fix TestRpcProgramNfs3 to use DFS_ENCRYPTION_KEY_PROVIDER_URI
     (clamb via cmccabe)
 
+    HDFS-7046. HA NN can NPE upon transition to active. (kihwal)
+
     BREAKDOWN OF HDFS-6134 AND HADOOP-10150 SUBTASKS AND RELATED JIRAS
   
       HDFS-6387. HDFS CLI admin tool for creating & deleting an
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
index 2b033628d04..4dc278667d1 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
@@ -1156,8 +1156,9 @@ void startActiveServices() throws IOException {
       cacheManager.startMonitorThread();
       blockManager.getDatanodeManager().setShouldSendCachingCommands(true);
     } finally {
-      writeUnlock();
       startingActiveService = false;
+      checkSafeMode();
+      writeUnlock();
     }
   }
 
@@ -5570,6 +5571,9 @@ private void checkMode() {
       // Have to have write-lock since leaving safemode initializes
       // repl queues, which requires write lock
       assert hasWriteLock();
+      if (inTransitionToActive()) {
+        return;
+      }
       // if smmthread is already running, the block threshold must have been 
       // reached before, there is no need to enter the safe mode again
       if (smmthread == null && needEnter()) {