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https://issues.apache.org/jira/browse/HDFS-3860?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13443271#comment-13443271
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Aaron T. Myers commented on HDFS-3860:
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Oof, good catch, Jing. Fortunately this case seems like it would be pretty
tough to hit, since if the NN is in SM then HeartbeatManager#heartbeatCheck
will return early, so to hit this the NN would have to enter SM in a very short
window of time. Still certainly worth fixing, though.
The patch looks good to me. The findbugs warning is unrelated and
TestHftpDelegationToken is known to currently be failing.
+1, I'll commit this momentarily.
> 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
> 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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