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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9137) DeadLock between DataNode#refreshVolumes and BPOfferService#registrationSucceeded
Date Thu, 08 Oct 2015 09:18:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14948350#comment-14948350

Hudson commented on HDFS-9137:

FAILURE: Integrated in Hadoop-Hdfs-trunk-Java8 #470 (See [https://builds.apache.org/job/Hadoop-Hdfs-trunk-Java8/470/])
HDFS-9137. DeadLock between DataNode#refreshVolumes and (yliu: rev 35affec38e17e3f9c21d36be111171476072c03f)
* hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
* hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

> 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
>             Fix For: 2.8.0
>         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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