HDFS-7884. Fix NullPointerException in BlockSender when the generation stamp provided by the client is larger than the one stored in the datanode. Contributed by Brahma Reddy Battula

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -1237,6 +1237,10 @@ Release 2.7.0 - UNRELEASED
 
     HDFS-7942. NFS: support regexp grouping in nfs.exports.allowed.hosts (brandonli)
 
+    HDFS-7884. Fix NullPointerException in BlockSender when the generation stamp
+    provided by the client is larger than the one stored in the datanode.
+    (Brahma Reddy Battula via szetszwo)
+
     BREAKDOWN OF HDFS-7584 SUBTASKS AND RELATED JIRAS
 
       HDFS-7720. Quota by Storage Type API, tools and ClientNameNode

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

@@ -246,6 +246,13 @@ class BlockSender implements java.io.Closeable {
       if (replica.getGenerationStamp() < block.getGenerationStamp()) {
         throw new IOException("Replica gen stamp < block genstamp, block="
             + block + ", replica=" + replica);
+      } else if (replica.getGenerationStamp() > block.getGenerationStamp()) {
+        if (DataNode.LOG.isDebugEnabled()) {
+          DataNode.LOG.debug("Bumping up the client provided"
+              + " block's genstamp to latest " + replica.getGenerationStamp()
+              + " for block " + block);
+        }
+        block.setGenerationStamp(replica.getGenerationStamp());
       }
       if (replicaVisibleLength < 0) {
         throw new IOException("Replica is not readable, block="