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IT31225: IBM MQ Managed File Transfers from a SFTP server occasionally hang

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APAR status

  • Closed as program error.

Error description

  • An IBM MQ V9.1.0.3 Managed File Transfer protocol bridge agent
    connects to a file server using the SFTP protocol, and acts as
    the source agent for managed transfers.
    
    Intermittently, a managed transfer being processed by the agent
    starts and then appears to hang.
    
    A Javacore from the agent taken when the managed transfer is
    stuck shows that an internal FileIOWorker thread has become
    blocked. An example of the call stack for this thread, as seen
    in the Javacore, is shown below:
    
    3XMTHREADINFO      "FileIOWorker-0:6"
    J9VMThread:0x0000000001B73F00, omrthread_t:0x00007F47400422E8,
     java/lang/Thread:0x00000000820A4ED8, state:CW, prio=5
    (java/lang/Thread getId:0x4F5, isDaemon:true)
    (native thread ID:0x18D81, native  priority:0x5, native
    policy:UNKNOWN, vmstate:CW, vm thread flags:0x00080181)
    (native stack address range from:0x00007F475513E000,
    to:0x00007F475517E000, size:0x40000)
    CPU usage total: 1.805280309 secs, current
    category="Application"
    Waiting on:
      com/jcraft/jsch/Channel$MyPipedInputStream@0x0000000082096278
    Owned by: <unowned>
    Heap bytes allocated since last GC cycle=0 (0x0)
    Java callstack:
    at java/lang/Object.wait(Native Method)
    at java/lang/Object.wait(Object.java:218(Compiled Code))
    at
    java/io/PipedInputStream.read(PipedInputStream.java:337(Compiled
     Code))
    (entered lock:
    com/jcraft/jsch/Channel$MyPipedInputStream@0x0000000082096278,
    entry count: 2)
    at
    java/io/PipedInputStream.read(PipedInputStream.java:388(Compiled
     Code))
    (entered lock:
    com/jcraft/jsch/Channel$MyPipedInputStream@0x0000000082096278,
    entry count: 1)
    at java/io/InputStream.skip(InputStream.java:246)
    at com/jcraft/jsch/ChannelSftp.skip(ChannelSftp.java:2921)
    at com/jcraft/jsch/ChannelSftp.access$600(ChannelSftp.java:36)
    at
    com/jcraft/jsch/ChannelSftp$RequestQueue.cancel(ChannelSftp.java
    :1270)
    at com/jcraft/jsch/ChannelSftp$2.read(ChannelSftp.java:1429)
    at
    java/io/DataInputStream.readFully(DataInputStream.java:206(Compi
    led Code))
    at
    com/ibm/wmqfte/io/bridge/BridgeFileChannelImpl.read(BridgeFileCh
    annelImpl.java:798)
    at
    com/ibm/wmqfte/io/bridge/BridgeFileChannelImpl.read(BridgeFileCh
    annelImpl.java:734)
    at
    com/ibm/wmqfte/transfer/frame/impl/TransferFrameSenderImpl.reque
    stChunk(TransferFrameSenderImpl.java:697)
    at
    com/ibm/wmqfte/transfer/frame/impl/TransferFrameSenderImpl.acces
    s$000(TransferFrameSenderImpl.java:95)
    at
    com/ibm/wmqfte/transfer/frame/impl/TransferFrameSenderImpl$Chunk
    Requester.processFileIORequest(TransferFrameSenderImpl.java:137)
    at
    com/ibm/wmqfte/transfer/frame/impl/TransferFrameIOWorker.doWorkI
    mpl(TransferFrameIOWorker.java:318)
    (entered lock: java/lang/Object@0x0000000082096000, entry count:
    1)
    at
    com/ibm/wmqfte/io/impl/FTEFileIOWorker.doWork(FTEFileIOWorker.ja
    va:118)
    at
    com/ibm/wmqfte/io/impl/FTEFileIORequestQueue.run(FTEFileIOReques
    tQueue.java:244)
    at java/lang/Thread.run(Thread.java:812)
    at com/ibm/wmqfte/thread/FTEThread.run(FTEThread.java:70)
    

Local fix

Problem summary

  • ****************************************************************
    USERS AFFECTED:
    This issue affects users of IBM MQ Managed File Transfer who
    have protocol bridge agents that:
    
    - Connect to file servers using the SFTP protocol.
    - And act as the source agent for managed transfers.
    
    
    Platforms affected:
    MultiPlatform
    
    ****************************************************************
    PROBLEM DESCRIPTION:
    IBM MQ Managed File Transfer includes a fork of the third-party
    JSch library.  This library is used by protocol bridge agents
    (PBAs) when communicating to file servers using the SFTP
    protocol. If a PBA is acting as the source agent for a managed
    transfer, it will make use of functions provided by JSch to
    connect to the file server and receive the file data for the
    source file.
    
    When reading file data from a file server, JSch sends a number
    of requests to the file server, asking for data. Each of these
    requests contains a sequence number, After the requests have
    been sent, JSch starts receiving the responses from the file
    server. The responses also contain a sequence number,
    corresponding to the request that the response is for.  JSch
    uses the sequence number in the response to ensure that the
    responses are received in the correct order.  After all of the
    responses have been received, JSch passes the file data back to
    the PBA for processing.
    
    If JSch detected that a response had arrived out of sequence, it
    would attempt to skip over this response, and then receive the
    next one.  However, due to an issue within the JSch code, the
    out of sequence response was not processed correctly.
    
    This led to undefined behaviour when trying to process
    subsequent responses which had been returned from the SFTP
    server.  This typically resulted in waiting for more data from
    the SFTP server than had been sent.  This in turn resulted in an
    internal FileIOWorker thread associated with a managed transfer
    within the PBA to hang.
    

Problem conclusion

  • To resolve this issue, the fork of the JSch library included
    with IBM MQ Managed File Transfer has been updated to ensure
    that out of order responses are processed correctly.  After the
    responses have been dealt with, the JSch library will request
    the file data from the file server again.  Once the file data
    has been successfully received, JSch will pass it back to the
    protocol bridge agent for processing.
    
    ---------------------------------------------------------------
    The fix is targeted for delivery in the following PTFs:
    
    Version    Maintenance Level
    v9.1 LTS   9.1.0.7
    v9.2 LTS   9.2.0.1
    v9.x CD    9.2.1
    
    The latest available MQ maintenance can be obtained from
    'WebSphere MQ Recommended Fixes'
    http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
    
    If the maintenance level is not yet available information on
    its planned availability can be found in 'WebSphere MQ
    Planned Maintenance Release Dates'
    http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
    ---------------------------------------------------------------
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT31225

  • Reported component name

    IBM MQ MFT V9.1

  • Reported component ID

    5724H7272

  • Reported release

    910

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2019-12-10

  • Closed date

    2020-07-02

  • Last modified date

    2020-11-13

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

Fix information

  • Fixed component name

    IBM MQ MFT V9.1

  • Fixed component ID

    5724H7272

Applicable component levels

[{"Line of Business":{"code":"LOB36","label":"IBM Automation"},"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Product":{"code":"SSYHRD","label":"IBM MQ"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"910"}]

Document Information

Modified date:
16 November 2020