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From "Kuhu Shukla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9958) BlockManager#createLocatedBlocks can throw NPE for corruptBlocks on failed storages.
Date Tue, 19 Apr 2016 13:25:25 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9958?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15247743#comment-15247743

Kuhu Shukla commented on HDFS-9958:

Thanks [~walter.k.su]. I looked at the test failure. I think the use of 'corruptReplicas'
for numMachines may have been a wrong choice. In a case where something leads to the inconsistent
state , for eg. {{findAndMarkBlockAsCorrupt}} adds the replica to the corruptsReplica Map
whether or not it is present in the blocksMap, the WARN log shows up but should not cause
the out of bounds exception. IMHO , we should use only blocksMap as much as possible to decide
the size of the array, which would mean that we fix {{countNodes().corruptReplicas()}} to
return the number after going thru all storages( irrespective of their state) that have the
corruptNodes (in this case), since {{numNodes()}} is storage state agnostic.

Would appreciate your comments on this and please correct me if I am missing something here.
Thanks a lot!

> BlockManager#createLocatedBlocks can throw NPE for corruptBlocks on failed storages.
> ------------------------------------------------------------------------------------
>                 Key: HDFS-9958
>                 URL: https://issues.apache.org/jira/browse/HDFS-9958
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.7.2
>            Reporter: Kuhu Shukla
>            Assignee: Kuhu Shukla
>         Attachments: HDFS-9958-Test-v1.txt, HDFS-9958.001.patch, HDFS-9958.002.patch
> In a scenario where the corrupt replica is on a failed storage, before it is taken out
of blocksMap, there is a race which causes the creation of LocatedBlock on a {{machines}}
array element that is not populated. 
> Following is the root cause,
> {code}
> final int numCorruptNodes = countNodes(blk).corruptReplicas();
> {code}
> countNodes only looks at nodes with storage state as NORMAL, which in the case where
corrupt replica is on failed storage will amount to numCorruptNodes being zero. 
> {code}
> final int numNodes = blocksMap.numNodes(blk);
> {code}
> However, numNodes will count all nodes/storages irrespective of the state of the storage.
Therefore numMachines will include such (failed) nodes. The assert would fail only if the
system is enabled to catch Assertion errors, otherwise it goes ahead and tries to create LocatedBlock
object for that is not put in the {{machines}} array.
> Here is the stack trace:
> {code}
> java.lang.NullPointerException
> 	at org.apache.hadoop.hdfs.server.blockmanagement.DatanodeStorageInfo.toDatanodeInfos(DatanodeStorageInfo.java:45)
> 	at org.apache.hadoop.hdfs.server.blockmanagement.DatanodeStorageInfo.toDatanodeInfos(DatanodeStorageInfo.java:40)
> 	at org.apache.hadoop.hdfs.protocol.LocatedBlock.<init>(LocatedBlock.java:84)
> 	at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.createLocatedBlock(BlockManager.java:878)
> 	at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.createLocatedBlock(BlockManager.java:826)
> 	at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.createLocatedBlockList(BlockManager.java:799)
> 	at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.createLocatedBlocks(BlockManager.java:899)
> 	at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getBlockLocationsInt(FSNamesystem.java:1849)
> 	at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getBlockLocations(FSNamesystem.java:1799)
> 	at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getBlockLocations(FSNamesystem.java:1712)
> 	at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.getBlockLocations(NameNodeRpcServer.java:588)
> 	at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.getBlockLocations(ClientNamenodeProtocolServerSideTranslatorPB.java:365)
> 	at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
> 	at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:616)
> 	at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:982)
> 	at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2049)
> 	at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2045)
> 	at java.security.AccessController.doPrivileged(Native Method)
> 	at javax.security.auth.Subject.doAs(Subject.java:415)
> 	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1657)
> 	at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2043)
> {code}

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