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https://issues.apache.org/jira/browse/HDFS-10512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15324552#comment-15324552
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Wei-Chiu Chuang commented on HDFS-10512:
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Thanks [~linyiqun] The check in the patch looks good to me.
I think that if the volume is null for some reason and can't report the bad
block to the NN, it should throw an IOException so that this not ignored. At
this point, I am not sure if it's some race condition in a bug somewhere.
> VolumeScanner may terminate to due NPE in DataNode.reportBadBlocks
> ------------------------------------------------------------------
>
> Key: HDFS-10512
> URL: https://issues.apache.org/jira/browse/HDFS-10512
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Wei-Chiu Chuang
> Assignee: Yiqun Lin
> Attachments: HDFS-10512.001.patch
>
>
> VolumeScanner may terminate due to unexpected NullPointerException thrown in
> {{DataNode.reportBadBlocks()}}. This is different from HDFS-8850/HDFS-9190
> I observed this bug in a production CDH 5.5.1 cluster and the same bug still
> persist in upstream trunk.
> {noformat}
> 2016-04-07 20:30:53,830 WARN
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner: Reporting bad
> BP-1800173197-10.204.68.5-1444425156296:blk_1170134484_96468685 on /dfs/dn
> 2016-04-07 20:30:53,831 ERROR
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner: VolumeScanner(/dfs/dn,
> DS-89b72832-2a8c-48f3-8235-48e6c5eb5ab3) exiting because of exception
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.datanode.DataNode.reportBadBlocks(DataNode.java:1018)
> at
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner$ScanResultHandler.handle(VolumeScanner.java:287)
> at
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner.scanBlock(VolumeScanner.java:443)
> at
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner.runLoop(VolumeScanner.java:547)
> at
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner.run(VolumeScanner.java:621)
> 2016-04-07 20:30:53,832 INFO
> org.apache.hadoop.hdfs.server.datanode.VolumeScanner: VolumeScanner(/dfs/dn,
> DS-89b72832-2a8c-48f3-8235-48e6c5eb5ab3) exiting.
> {noformat}
> I think the NPE comes from the volume variable in the following code snippet.
> Somehow the volume scanner know the volume, but the datanode can not lookup
> the volume using the block.
> {code}
> public void reportBadBlocks(ExtendedBlock block) throws IOException{
> BPOfferService bpos = getBPOSForBlock(block);
> FsVolumeSpi volume = getFSDataset().getVolume(block);
> bpos.reportBadBlocks(
> block, volume.getStorageID(), volume.getStorageType());
> }
> {code}
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