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https://issues.apache.org/jira/browse/HDFS-9137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14943128#comment-14943128
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Vinayakumar B commented on HDFS-9137:
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I agree with [~hitliuyi], exception could be thrown directly. I think Uma
trying not to hide the original exception, in case triggerBlockReport throws
any exception.
And I see, triggering block reports may not be required in case of unchanged
configurations. Currently w/ or w/o patch, blockreports are getting triggered
when there is nothing changed.
This also could be considered, to reduce the load on NameNode on unnecessary
block report processing?
> DeadLock between DataNode#refreshVolumes and
> BPOfferService#registrationSucceeded
> ----------------------------------------------------------------------------------
>
> Key: HDFS-9137
> URL: https://issues.apache.org/jira/browse/HDFS-9137
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 3.0.0, 2.7.1
> Reporter: Uma Maheswara Rao G
> Assignee: Uma Maheswara Rao G
> Attachments: HDFS-9137.00.patch
>
>
> I can see this code flows between DataNode#refreshVolumes and
> BPOfferService#registrationSucceeded could cause deadLock.
> In practice situation may be rare as user calling refreshVolumes at the time
> DN registration with NN. But seems like issue can happen.
> Reason for deadLock:
> 1) refreshVolumes will be called with DN lock and after at the end it will
> also trigger Block report. In the Block report call,
> BPServiceActor#triggerBlockReport calls toString on bpos. Here it takes
> readLock on bpos.
> DN lock then boos lock
> 2) BPOfferSetrvice#registrationSucceeded call is taking writeLock on bpos and
> calling dn.bpRegistrationSucceeded which is again synchronized call on DN.
> bpos lock and then DN lock.
> So, this can clearly create dead lock.
> I think simple fix could be to move triggerBlockReport call outside out DN
> lock and I feel that call may not be really needed inside DN lock.
> Thoughts?
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