[HDFS-4482] ReplicationMonitor thread can exit with NPE due to the race between delete and replication of same file.

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 2.0.1-alpha, 3.0.0-alpha1
• Fix Version/s: 2.0.5-alpha, 0.23.10
• Component/s: namenode
• Target Version/s: 2.1.0-beta
• Hadoop Flags: Reviewed
• Assignee: Uma Maheswara Rao G
• Reporter: Uma Maheswara Rao G
• Created: 08/Feb/13 09:58
• Updated: 12/May/16 18:17
• Resolved: 21/Feb/13 16:52

Description

Trace:

java.lang.NullPointerException
	at org.apache.hadoop.hdfs.server.namenode.FSDirectory.getFullPathName(FSDirectory.java:1442)
	at org.apache.hadoop.hdfs.server.namenode.INode.getFullPathName(INode.java:269)
	at org.apache.hadoop.hdfs.server.namenode.INodeFile.getName(INodeFile.java:163)
	at org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy.chooseTarget(BlockPlacementPolicy.java:131)
	at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWorkForBlocks(BlockManager.java:1157)
	at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWork(BlockManager.java:1063)
	at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeDatanodeWork(BlockManager.java:3085)
	at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$ReplicationMonitor.run(BlockManager.java:3047)
	at java.lang.Thread.run(Thread.java:619)

What I am seeing here is:

1) create a file and write with 2 DNS
2) Close the file.
3) Kill one DN
4) Let replication start.
Info:

 // choose replication targets: NOT HOLDING THE GLOBAL LOCK
      // It is costly to extract the filename for which chooseTargets is called,
      // so for now we pass in the block collection itself.
      rw.targets = blockplacement.chooseTarget(rw.bc,
          rw.additionalReplRequired, rw.srcNode, rw.liveReplicaNodes,
          excludedNodes, rw.block.getNumBytes());

Here we are choosing target outside the global lock. Inside we will try to get the src path from blockCollection(nothing but INodeFile here).

see the code for FSDirectory#getFullPathName
Here it is incrementing the depth until it has parent. and Later it will iterate and access parent again in next loop.

5) before going to secnd loop in FSDirectory#getFullPathName, if file is deleted by client then that parent would have been set as null. So, here accessing the parent can cause NPE because it is not under lock.

brahmareddy reported this issue.

Issue Links

• duplicates: HDFS-5142 Namenode crashes with NPE in ReplicationMonitor