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https://issues.apache.org/jira/browse/HDFS-9137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14946085#comment-14946085
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Yi Liu commented on HDFS-9137:
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I think it's OK to do the fix using this approach and update the
{{BPOS#toString()}} in a follow-on.
The new patch looks good to me, +1 pending Jeninks, thanks Uma, Vinay, Colin.
How do you think [~vinayrpet], [~cmccabe]?
> 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,
> HDFS-9137.01-WithPreservingRootExceptions.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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