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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-9676) Deadlock during canceling task and recycling exclusive buffer
Date Tue, 10 Jul 2018 09:23:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9676?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16538305#comment-16538305
] 

ASF GitHub Bot commented on FLINK-9676:
---------------------------------------

Github user NicoK commented on a diff in the pull request:

    https://github.com/apache/flink/pull/6254#discussion_r201273133
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/io/network/partition/consumer/RemoteInputChannel.java
---
    @@ -479,6 +508,9 @@ void onSenderBacklog(int backlog) throws IOException {
     
     			numRequiredBuffers = backlog + initialCredit;
     			while (bufferQueue.getAvailableBufferSize() < numRequiredBuffers && !isWaitingForFloatingBuffers)
{
    +				// TODO: this will take a lock in the LocalBufferPool as well and needs to be done
    +				// outside the synchronized block (which is a bit difficult trying to acquire the
    +				// lock only once!
     				Buffer buffer = inputGate.getBufferPool().requestBuffer();
    --- End diff --
    
    I'm not sure about this change since this may lead to lower-throughput channels being
starved by high-throughput channels, but we can discuss further with a broader audience in
the JIRA ticket once created (this is off-topic here)


> Deadlock during canceling task and recycling exclusive buffer
> -------------------------------------------------------------
>
>                 Key: FLINK-9676
>                 URL: https://issues.apache.org/jira/browse/FLINK-9676
>             Project: Flink
>          Issue Type: Bug
>          Components: Network
>    Affects Versions: 1.5.0
>            Reporter: zhijiang
>            Assignee: Nico Kruber
>            Priority: Critical
>              Labels: pull-request-available
>             Fix For: 1.5.1, 1.6.0
>
>
> It may cause deadlock between task canceler thread and task thread.
> The detail is as follows:
> {{Task canceler thread -> IC1#releaseAllResources -> recycle floating buffers -> {color:#d04437}lock{color}(LocalBufferPool#availableMemorySegments)
-> IC2#notifyBufferAvailable}} > {color:#d04437}try to lock{color}(IC2#bufferQueue)
> {{Task thread -> IC2#recycle -> {color:#d04437}lock{color}(IC2#bufferQueue) ->
bufferQueue#addExclusiveBuffer}} -> {{floatingBuffer#recycleBuffer}} -> {color:#d04437}try
to lock{color}(LocalBufferPool#availableMemorySegments)
> One solution is that {{listener#notifyBufferAvailable}} can be called outside the
{{synchronized(availableMemorySegments) in }}{{LocalBufferPool#recycle.}}
> The existing RemoteInputChannelTest#testConcurrentOnSenderBacklogAndRecycle can cover
this case but the deadlock probability is very low, so this UT is not stable.



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