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From "Rakesh R (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5832) Deadeadlock found in NN between SafeMode#canLeave and DatanodeManager#handleHeartbeat
Date Sat, 25 Jan 2014 15:43:38 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13881927#comment-13881927
] 

Rakesh R commented on HDFS-5832:
--------------------------------

Thanks Uma for the interest.
Looks like similar, but I could see still there is a chance of reverse locking in the code.


I'm seeing the following code flow like,
- In one side, when running SafeModeMonitor thread, it is invoking safeMode#canLeave() by
acquiring 'safeMode.this' lock and here it is asking for the DataNodeManger#getNumLiveDataNodes
by trying to acquire 'datanodeMap' lock.
- On the other side, DN heartbeat comes and DatanodeManager#handleHeartbeat() has acquired
'datanodeMap' lock and calling namesystem#isInSafeMode(), which inturn trying to acquire 'safeModeInfo.this'
lock

> Deadeadlock found in NN between SafeMode#canLeave and DatanodeManager#handleHeartbeat
> -------------------------------------------------------------------------------------
>
>                 Key: HDFS-5832
>                 URL: https://issues.apache.org/jira/browse/HDFS-5832
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 3.0.0
>            Reporter: Rakesh R
>            Assignee: Rakesh R
>            Priority: Blocker
>         Attachments: HDFS-5832.patch, jcarder_nn_deadlock.gif
>
>
> Found the deadlock during the Namenode startup. Attached jcarder report which shows the
cycles about the deadlock situation.



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