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https://issues.apache.org/jira/browse/HDFS-862?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Todd Lipcon updated HDFS-862:
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Attachment: cycle.png
Here's the graph of the lock cycle.
> Potential NN deadlock in processDistributedUpgradeCommand
> ---------------------------------------------------------
>
> Key: HDFS-862
> URL: https://issues.apache.org/jira/browse/HDFS-862
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: name-node
> Affects Versions: 0.22.0
> Reporter: Todd Lipcon
> Attachments: cycle.png
>
>
> Haven't seen this in practice, but the lock order is inconsistent.
> processReport locks FSNamesystem, then calls UpgradeManager.startUpgrade,
> getUpgradeState, and getUpgradeStatus (each of which locks the
> UpgradeManager). FSNameSystem.processDistributedUpgradeCommand calls
> upgradeManager.processUpgradeCommand which is synchronized on UpgradeManager,
> which can call FSNameSystem.leaveSafeMode which synchronizes on FSNamesystem.
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