diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index 793ce5b8e65..a781e320495 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -348,6 +348,9 @@ Release 2.3.0 - UNRELEASED
 
   BUG FIXES
 
+    HADOOP-9964. Fix deadlocks in TestHttpServer by synchronize
+    ReflectionUtils.printThreadInfo. (Junping Du via llu)
+
     HADOOP-9582. Non-existent file to "hadoop fs -conf" doesn't throw error
     (Ashwin Shankar via jlowe)
 
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/ReflectionUtils.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/ReflectionUtils.java
index 4fee5f4f952..be63c816201 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/ReflectionUtils.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/ReflectionUtils.java
@@ -154,7 +154,7 @@ public class ReflectionUtils {
    * @param stream the stream to
    * @param title a string title for the stack trace
    */
-  public static void printThreadInfo(PrintWriter stream,
+  public synchronized static void printThreadInfo(PrintWriter stream,
                                      String title) {
     final int STACK_DEPTH = 20;
     boolean contention = threadBean.isThreadContentionMonitoringEnabled();