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From "Tao Yang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-6029) CapacityScheduler deadlock when ParentQueue#getQueueUserAclInfo is called by Thread_A at the moment that Thread_B calls LeafQueue#assignContainers to release a reserved container
Date Wed, 28 Dec 2016 03:51:58 GMT

    [ https://issues.apache.org/jira/browse/YARN-6029?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15781969#comment-15781969
] 

Tao Yang commented on YARN-6029:
--------------------------------

Thanks [~Naganarasimha] [~djp] [~leftnoteasy] for your suggestions. 
[~Naganarasimha] I think there maybe have a problem when iterating childQueues and at the
same time ParentQueue#setChildQueues is called.
[~leftnoteasy] I agree your solution solves the problem. But I still think synchronized modifier
of LeafQueue#getQueueUserAclInfo is not required. In my opinion, This method doesn't affect
the data structure of LeafQueue instance (check permissions of the given user, create new
QueueUserACLInfo instance then return.), and it's only called by ParentQueue#getQueueUserAclInfo.
By the way, take FairScheduler as a reference, FSLeafQueue#getQueueUserAclInfo is not synchronized.
Maybe I haven't realized the potential problem, Please correct me if I am wrong.

> CapacityScheduler deadlock when ParentQueue#getQueueUserAclInfo is called by Thread_A
at the moment that Thread_B calls LeafQueue#assignContainers to release a reserved container
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: YARN-6029
>                 URL: https://issues.apache.org/jira/browse/YARN-6029
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: capacityscheduler
>    Affects Versions: 2.8.0
>            Reporter: Tao Yang
>            Assignee: Tao Yang
>            Priority: Blocker
>         Attachments: YARN-6029.001.patch, deadlock.jstack
>
>
> When ParentQueue#getQueueUserAclInfo is called (e.g. a client calls YarnClient#getQueueAclsInfo)
just at the moment that LeafQueue#assignContainers is called and before notifying parent queue
to release resource (should release a reserved container), then ResourceManager can deadlock.
I found this problem on our testing environment for hadoop2.8.
> Reproduce the deadlock in chronological order
> * 1. Thread A (ResourceManager Event Processor) calls synchronized LeafQueue#assignContainers
(got LeafQueue instance lock of queue root.a)
> * 2. Thread B (IPC Server handler) calls synchronized ParentQueue#getQueueUserAclInfo
(got ParentQueue instance lock of queue root), iterates over children queue acls and is blocked
when calling synchronized LeafQueue#getQueueUserAclInfo (the LeafQueue instance lock of queue
root.a is hold by Thread A)
> * 3. Thread A wants to inform the parent queue that a container is being completed and
is blocked when invoking synchronized ParentQueue#internalReleaseResource method (the ParentQueue
instance lock of queue root is hold by Thread B)
> I think the synchronized modifier of LeafQueue#getQueueUserAclInfo can be removed to
solve this problem, since this method appears to not affect fields of LeafQueue instance.
> Attach patch with UT for review.



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