svn merge -c 1378228 FIXES: HDFS-3860. HeartbeatManager#Monitor may wrongly hold the writelock of namesystem. Contributed by Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1390632 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -12,6 +12,9 @@ Release 0.23.4 - UNRELEASED
 
   BUG FIXES
 
+    HDFS-3860. HeartbeatManager#Monitor may wrongly hold the writelock of
+    namesystem. (Jing Zhao via atm)
+
 Release 0.23.3 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/HeartbeatManager.java

@@ -223,10 +223,10 @@ class HeartbeatManager implements DatanodeStatistics {
       if (!allAlive) {
         // acquire the fsnamesystem lock, and then remove the dead node.
         namesystem.writeLock();
-        if (namesystem.isInSafeMode()) {
-          return;
-        }
         try {
+          if (namesystem.isInSafeMode()) {
+            return;
+          }
           synchronized(this) {
             dm.removeDeadDatanode(dead);
           }