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https://issues.apache.org/jira/browse/MAPREDUCE-1342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12797552#action_12797552
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Amar Kamat commented on MAPREDUCE-1342:
---------------------------------------
Had a brief discussion with Amareshwari on this. Looks like only
JobTracker.activeTaskTrackers() and JobTracker.blacklistedTaskTrackers() are
calling JobTracker.FaultyTrackerInfo.isBlacklisted() without the JobTracker
lock. So extending the comment
[here|https://issues.apache.org/jira/browse/MAPREDUCE-1342?focusedCommentId=12796996&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_12796996],
I think we can do something like
{code}
FaultyTrackersInfo {
getTaskTrackers(boolean blacklisted) {
synchronized (potentiallyFaultyTrackers) {
synchronized (taskTrackers) {
// code that we have today JobTracker.blacklistedTaskTrackers()
for (TaskTracker tt : taskTrackers.values()) {
if (isBlacklisted(tt) equals blacklisted) {
// add to return set
}
}
}
}
}
}
blacklistedTaskTrackers() {
return FaultyTrackersInfo.getTaskTrackers(true)
}
activeTaskTrackers() {
return FaultyTrackersInfo.getTaskTrackers(false)
}
{code}
Currently, activeTaskTrackers() and blacklistedTaskTrackers() differ only on
the condition whether the tasktracker is faulty or not. 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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