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From NicoK <...@git.apache.org>
Subject [GitHub] flink pull request #6254: [FLINK-9676][network] clarify contracts of BufferL...
Date Wed, 04 Jul 2018 14:48:17 GMT
GitHub user NicoK opened a pull request:

    https://github.com/apache/flink/pull/6254

    [FLINK-9676][network] clarify contracts of BufferListener#notifyBufferAvailable() and
fix a deadlock

    ## What is the purpose of the change
    
    When recycling exclusive buffers of a `RemoteInputChannel` and recycling (other/floating)
buffers to the buffer pool concurrently while the `RemoteInputChannel` is registered as a
listener to the buffer pool and adding the exclusive buffer triggers a floating buffer to
be recycled back to the same
    buffer pool, a deadlock would occur holding locks on `LocalBufferPool#availableMemorySegments`
and `RemoteInputChannel#bufferQueue` but acquiring them in reverse order.
    
    One such instance would be (thanks @zhijiangW for finding this):
    
    ```
    Task canceler thread -> RemoteInputChannel1#releaseAllResources -> recycle floating
buffers
     -> lock(LocalBufferPool#availableMemorySegments) -> RemoteInputChannel2#notifyBufferAvailable
     -> try to lock(RemoteInputChannel2#bufferQueue)
    ```
    ```
    Task thread -> RemoteInputChannel2#recycle
     -> lock(RemoteInputChannel2#bufferQueue) -> bufferQueue#addExclusiveBuffer ->
floatingBuffer#recycleBuffer
     -> try to lock(LocalBufferPool#availableMemorySegments)
    ```
    
    @pnowojski and @tillrohrmann can you also have a quick look so that this can get into
1.5.1?
    
    ## Brief change log
    
    - clarify the contract of `BufferListener#notifyBufferAvailable()` (see in the code)
    - make sure that none of the places in `RemoteInputChannel` break this contract, i.e.
wherever a lock on `bufferQueue` is taken, we may not recycle any buffer under this lock
    
    ## Verifying this change
    
    This change added tests and can be verified as follows:
    
    - added `RemoteInputChannelTest#testConcurrentRecycleAndRelease2` which catches this deadlock
quite quickly
    
    ## Does this pull request potentially affect one of the following parts:
    
      - Dependencies (does it add or upgrade a dependency): **no**
      - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: **no**
      - The serializers: **no**
      - The runtime per-record code paths (performance sensitive): **no** (per buffer, but
we're only moving recycling out of the synchronized block so if there's any effect, it should
be positive)
      - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing,
Yarn/Mesos, ZooKeeper: **no**
      - The S3 file system connector: **no**
    
    ## Documentation
    
      - Does this pull request introduce a new feature? **no**
      - If yes, how is the feature documented? **JavaDocs**


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/NicoK/flink flink-9676

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/flink/pull/6254.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #6254
    
----
commit 14000788b71910f6026a448c9cb5b2f35e4b33dd
Author: Nico Kruber <nico@...>
Date:   2018-07-04T14:32:11Z

    [FLINK-9676][network] clarify contracts of BufferListener#notifyBufferAvailable() and
fix a deadlock
    
    When recycling exclusive buffers of a RemoteInputChannel and recycling
    (other/floating) buffers to the buffer pool concurrently while the
    RemoteInputChannel is registered as a listener to the buffer pool and adding the
    exclusive buffer triggers a floating buffer to be recycled back to the same
    buffer pool, a deadlock would occur holding locks on
    LocalBufferPool#availableMemorySegments and RemoteInputChannel#bufferQueue but
    acquiring them in reverse order.
    
    One such instance would be:
    
    Task canceler thread -> IC1#releaseAllResources -> recycle floating buffers
     -> lock(LocalBufferPool#availableMemorySegments) -> IC2#notifyBufferAvailable
     -> try to lock(IC2#bufferQueue)
    
    Task thread -> IC2#recycle
     -> lock(IC2#bufferQueue) -> bufferQueue#addExclusiveBuffer -> floatingBuffer#recycleBuffer
     -> try to lock(LocalBufferPool#availableMemorySegments)

----


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