Uma Maheswara Rao G created HDFS-4482:
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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
Trace:
{noformat}
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)
{noformat}
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.
Info:
{code}
// 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());
{code}
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.
2)
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