diff --git a/hadoop-mapreduce-project/CHANGES.txt b/hadoop-mapreduce-project/CHANGES.txt
index c579981c8e..e357080245 100644
--- a/hadoop-mapreduce-project/CHANGES.txt
+++ b/hadoop-mapreduce-project/CHANGES.txt
@@ -89,6 +89,9 @@ Release 0.23.1 - Unreleased
     MAPREDUCE-3342. Fixed JobHistoryServer to also show the job's queue
     name. (Jonathan Eagles via vinodkv)
 
+    MAPREDUCE-3345. Fixed a race condition in ResourceManager that was causing
+    TestContainerManagerSecurity to fail sometimes. (Hitesh Shah via vinodkv)
+
 Release 0.23.0 - 2011-11-01 
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/rmapp/attempt/RMAppAttemptImpl.java b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/rmapp/attempt/RMAppAttemptImpl.java
index 0d81f80121..71dd982b60 100644
--- a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/rmapp/attempt/RMAppAttemptImpl.java
+++ b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/rmapp/attempt/RMAppAttemptImpl.java
@@ -595,8 +595,13 @@ public void transition(RMAppAttemptImpl appAttempt,
           AM_CONTAINER_PRIORITY, "*", appAttempt.submissionContext
               .getAMContainerSpec().getResource(), 1);
 
-      appAttempt.scheduler.allocate(appAttempt.applicationAttemptId,
-          Collections.singletonList(request), EMPTY_CONTAINER_RELEASE_LIST);
+      Allocation amContainerAllocation = 
+          appAttempt.scheduler.allocate(appAttempt.applicationAttemptId,
+              Collections.singletonList(request), EMPTY_CONTAINER_RELEASE_LIST);
+      if (amContainerAllocation != null
+          && amContainerAllocation.getContainers() != null) {
+        assert(amContainerAllocation.getContainers().size() == 0);
+      }
     }
   }
 
diff --git a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/FifoScheduler.java b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/FifoScheduler.java
index c61c7ab89f..977150520a 100644
--- a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/FifoScheduler.java
+++ b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/FifoScheduler.java
@@ -236,28 +236,30 @@ public Allocation allocate(
           RMContainerEventType.RELEASED);
     }
 
-    if (!ask.isEmpty()) {
-      LOG.debug("allocate: pre-update" +
-          " applicationId=" + applicationAttemptId + 
-          " application=" + application);
-      application.showRequests();
+    synchronized (application) {
+      if (!ask.isEmpty()) {
+        LOG.debug("allocate: pre-update" +
+            " applicationId=" + applicationAttemptId + 
+            " application=" + application);
+        application.showRequests();
 
-      // Update application requests
-      application.updateResourceRequests(ask);
+        // Update application requests
+        application.updateResourceRequests(ask);
 
-      LOG.debug("allocate: post-update" +
-          " applicationId=" + applicationAttemptId + 
-          " application=" + application);
-      application.showRequests();
+        LOG.debug("allocate: post-update" +
+            " applicationId=" + applicationAttemptId + 
+            " application=" + application);
+        application.showRequests();
 
-      LOG.debug("allocate:" +
-          " applicationId=" + applicationAttemptId + 
-          " #ask=" + ask.size());
+        LOG.debug("allocate:" +
+            " applicationId=" + applicationAttemptId + 
+            " #ask=" + ask.size());
+      }
+
+      return new Allocation(
+          application.pullNewlyAllocatedContainers(), 
+          application.getHeadroom());
     }
-
-    return new Allocation(
-        application.pullNewlyAllocatedContainers(), 
-        application.getHeadroom());
   }
 
   private SchedulerApp getApplication(