HDFS-13721. NPE in DataNode due to uninitialized DiskBalancer.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

@@ -3132,7 +3132,7 @@ public class DataNode extends ReconfigurableBase
   @Override // DataNodeMXBean
   public String getDiskBalancerStatus() {
     try {
-      return this.diskBalancer.queryWorkStatus().toJsonString();
+      return getDiskBalancer().queryWorkStatus().toJsonString();
     } catch (IOException ex) {
       LOG.debug("Reading diskbalancer Status failed. ex:{}", ex);
       return "";
@@ -3510,7 +3510,7 @@ public class DataNode extends ReconfigurableBase
           DiskBalancerException.Result.DATANODE_STATUS_NOT_REGULAR);
     }
 
-    this.diskBalancer.submitPlan(planID, planVersion, planFile, planData,
+    getDiskBalancer().submitPlan(planID, planVersion, planFile, planData,
             skipDateCheck);
   }
 
@@ -3522,7 +3522,7 @@ public class DataNode extends ReconfigurableBase
   public void cancelDiskBalancePlan(String planID) throws
       IOException {
     checkSuperuserPrivilege();
-    this.diskBalancer.cancelPlan(planID);
+    getDiskBalancer().cancelPlan(planID);
   }
 
   /**
@@ -3533,7 +3533,7 @@ public class DataNode extends ReconfigurableBase
   @Override
   public DiskBalancerWorkStatus queryDiskBalancerPlan() throws IOException {
     checkSuperuserPrivilege();
-    return this.diskBalancer.queryWorkStatus();
+    return getDiskBalancer().queryWorkStatus();
   }
 
   /**
@@ -3550,9 +3550,9 @@ public class DataNode extends ReconfigurableBase
     Preconditions.checkNotNull(key);
     switch (key) {
     case DiskBalancerConstants.DISKBALANCER_VOLUME_NAME:
-      return this.diskBalancer.getVolumeNames();
+      return getDiskBalancer().getVolumeNames();
     case DiskBalancerConstants.DISKBALANCER_BANDWIDTH :
-      return Long.toString(this.diskBalancer.getBandwidth());
+      return Long.toString(getDiskBalancer().getBandwidth());
     default:
       LOG.error("Disk Balancer - Unknown key in get balancer setting. Key: {}",
           key);
@@ -3606,4 +3606,11 @@ public class DataNode extends ReconfigurableBase
     }
     return volumeInfoList;
   }
+
+  private DiskBalancer getDiskBalancer() throws IOException {
+    if (this.diskBalancer == null) {
+      throw new IOException("DiskBalancer is not initialized");
+    }
+    return this.diskBalancer;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/diskbalancer/TestDiskBalancer.java

@@ -109,6 +109,11 @@ public class TestDiskBalancer {
           .getFsVolumeReferences()) {
         assertEquals(ref.size(), dbDnNode.getVolumeCount());
       }
+
+      // Shutdown the DN first, to verify that calling diskbalancer APIs on
+      // uninitialized DN doesn't NPE
+      dnNode.shutdown();
+      assertEquals("", dnNode.getDiskBalancerStatus());
     } finally {
       cluster.shutdown();
     }