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From "Uma Maheswara Rao G (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-4482) ReplicationMonitor thread can exit with NPE due to the race between delete and replication of same file.
Date Fri, 08 Feb 2013 09:59:13 GMT
Uma Maheswara Rao G created HDFS-4482:

             Summary: ReplicationMonitor thread can exit with NPE due to the race between
delete and replication of same file.
                 Key: HDFS-4482
                 URL: https://issues.apache.org/jira/browse/HDFS-4482
             Project: Hadoop HDFS
          Issue Type: Bug
            Reporter: Uma Maheswara Rao G
            Priority: Blocker


	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) Lat replication start.
 // 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.

Between this 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.


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