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https://issues.apache.org/jira/browse/MAPREDUCE-1342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12797560#action_12797560
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Arun C Murthy commented on MAPREDUCE-1342:
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Hmm... first I think it's clear that this is a critical bug to be fixed asap.
Given the extremely fragile nature of the locking structure in the JobTracker
I'm very, very scared to make much changes here...
How about a simpler proposal: Let's make JobTracker.activeTaskTrackers() and
JobTracker.blacklistedTaskTrackers() synchronized methods. First these are
called only from the jsps, second this will sweep the inverted locking order
under the carpet of having to lock the JobTracker itself - thus solving the
deadlock.
I realize this is very ugly and I'm cringing as I suggest this, but I do value
the fact that this will do away with the need for more significant changes -
changes I'm very leery of!
Thoughts?
> Potential JT deadlock in faulty TT tracking
> -------------------------------------------
>
> Key: MAPREDUCE-1342
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1342
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: jobtracker
> Affects Versions: 0.22.0
> Reporter: Todd Lipcon
> Attachments: cycle0.png, mapreduce-1342-1.patch,
> mapreduce-1342-2.patch
>
>
> JT$FaultyTrackersInfo.incrementFaults first locks potentiallyFaultyTrackers,
> and then calls blackListTracker, which calls removeHostCapacity, which locks
> JT.taskTrackers
> On the other hand, JT.blacklistedTaskTrackers() locks taskTrackers, then
> calls faultyTrackers.isBlacklisted() which goes on to lock
> potentiallyFaultyTrackers.
> I haven't produced such a deadlock, but the lock ordering here is inverted
> and therefore could deadlock.
> Not sure if this goes back to 0.21 or just in trunk.
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