diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 0a68720d60..48ebda3437 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -395,6 +395,9 @@ Release 2.1.1-beta - UNRELEASED
     HDFS-5124. DelegationTokenSecretManager#retrievePassword can cause deadlock 
     in NameNode. (Daryn Sharp via jing9)
 
+    HDFS-5132. Deadlock in NameNode between SafeModeMonitor#run and 
+    DatanodeManager#handleHeartbeat. (kihwal)
+
 Release 2.1.0-beta - 2013-08-22
 
   INCOMPATIBLE CHANGES
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 569f2165c7..178f3d9b08 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
@@ -4798,7 +4798,21 @@ class SafeModeMonitor implements Runnable {
      */
     @Override
     public void run() {
-      while (fsRunning && (safeMode != null && !safeMode.canLeave())) {
+      while (fsRunning) {
+        writeLock();
+        try {
+          if (safeMode == null) { // Not in safe mode.
+            break;
+          }
+          if (safeMode.canLeave()) {
+            // Leave safe mode.
+            safeMode.leave();
+            break;
+          }
+        } finally {
+          writeUnlock();
+        }
+
         try {
           Thread.sleep(recheckInterval);
         } catch (InterruptedException ie) {
@@ -4807,9 +4821,6 @@ public void run() {
       }
       if (!fsRunning) {
         LOG.info("NameNode is being shutdown, exit SafeModeMonitor thread");
-      } else {
-        // leave safe mode and stop the monitor
-        leaveSafeMode();
       }
       smmthread = null;
     }