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https://issues.apache.org/jira/browse/HDFS-3860?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13443292#comment-13443292
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Jing Zhao commented on HDFS-3860:
---------------------------------

I just checked all the invocation of namesystem#writelock / writeunlock, and 
did not find similar problems. I will check other similar code too.
                
> HeartbeatManager#Monitor may wrongly hold the writelock of namesystem
> ---------------------------------------------------------------------
>
>                 Key: HDFS-3860
>                 URL: https://issues.apache.org/jira/browse/HDFS-3860
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 3.0.0
>            Reporter: Jing Zhao
>            Assignee: Jing Zhao
>             Fix For: 2.2.0-alpha
>
>         Attachments: HDFS-3860.patch, HDFS-heartbeat-testcase.patch
>
>
> In HeartbeatManager#heartbeatCheck, if some dead datanode is found, the 
> monitor thread will acquire the write lock of namesystem, and recheck the 
> safemode. If it is in safemode, the monitor thread will return from the 
> heartbeatCheck function without release the write lock. This may cause the 
> monitor thread wrongly holding the write lock forever.
> The attached test case tries to simulate this bad scenario.

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