diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 6063ba51f0..af5d1fdd0e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -241,6 +241,9 @@ Trunk (Unreleased)
     HDFS-4115. TestHDFSCLI.testAll fails one test due to number format.
     (Trevor Robinson via suresh)
 
+    HDFS-4106. BPServiceActor#lastHeartbeat, lastBlockReport and
+    lastDeletedReport should be volatile. (Jing Zhao via suresh)
+
   BREAKDOWN OF HDFS-3077 SUBTASKS
 
     HDFS-3077. Quorum-based protocol for reading and writing edit logs.
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BPServiceActor.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BPServiceActor.java
index 4f00daaef5..4bbada2c02 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BPServiceActor.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BPServiceActor.java
@@ -75,14 +75,18 @@ class BPServiceActor implements Runnable {
 
   BPOfferService bpos;
   
-  long lastBlockReport = 0;
-  long lastDeletedReport = 0;
+  // lastBlockReport, lastDeletedReport and lastHeartbeat may be assigned/read
+  // by testing threads (through BPServiceActor#triggerXXX), while also 
+  // assigned/read by the actor thread. Thus they should be declared as volatile
+  // to make sure the "happens-before" consistency.
+  volatile long lastBlockReport = 0;
+  volatile long lastDeletedReport = 0;
 
   boolean resetBlockReportTime = true;
 
   Thread bpThread;
   DatanodeProtocolClientSideTranslatorPB bpNamenode;
-  private long lastHeartbeat = 0;
+  private volatile long lastHeartbeat = 0;
   private volatile boolean initialized = false;
   
   /**