IBM Support

PH27505: WLM CAN GET IN A LOOP WHEN RECEIVING COMPRESSED DATA RUNNING ON Z15 HARDWARE

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APAR status

  • Closed as program error.

Error description

  • When WLM is decompressing data received it can get in a loop,
    the following stack can be seen in javacore:
    
    at java/util/Arrays.copyOf(Arrays.java:3580(Compiled Code))
    at
    java/io/ByteArrayOutputStream.grow(ByteArrayOutputStream.java:12
    9(Compiled Code))
    at
    java/io/ByteArrayOutputStream.ensureCapacity(ByteArrayOutputStre
    am.java:104(Compiled Code))
    at
    java/io/ByteArrayOutputStream.write(ByteArrayOutputStream.java:1
    64(Compiled Code))
    (entered lock: java/io/ByteArrayOutputStream@0x000000002A454E50,
    entry count: 1)
    at
    com/ibm/ws/cluster/Compressor.decompress(Compressor.java:219(Com
    piled Code))
    (entered lock: java/util/zip/Inflater@0x0000000019BA5000, entry
    count: 1)
    

Local fix

  • N/A
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:  Users of IBM WebSphere Application Server   *
    *                  Network Deployment using Linux on z15       *
    *                  hardware                                    *
    *                  with hardware compression enabled           *
    ****************************************************************
    * PROBLEM DESCRIPTION: An apparent hang occurs in the server,  *
    *                      with high CPU consumption and steady    *
    *                      memory growth                           *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    A defect (IJ26478) exists in Linux on zSeries Java levels prior
    to 8.0.6.16 wherein, when hardware compression is enabled on z15
    systems, the compressed data is invalid in a way that can
    prevent decompression processes from detecting that the
    decompression has actually finished.
    In this specific case, the Work Load Manager component
    compresses cluster description data to send to other processes.
    When that data is decompressed, the failure to read the end of
    the compressed data results in an endless loop that also adds
    bytes to a data structure. In that case, the process will hang
    until eventually running out memory.
    

Problem conclusion

  • Mitigation was added to the Work Load Manager component to avoid
    the endless loop. Note that there are other potential issues
    caused by the faulty data compression, and for that reason
    IJ26478 should be applied even if this APAR is present.
    
    The fix for this APAR is targeted for inclusion in fix packs
    8.5.5.19 and 9.0.5.7. For more information, see 'Recommended
    Updates for WebSphere Application Server':
    https://www.ibm.com/support/pages/node/715553
    

Temporary fix

Comments

APAR Information

  • APAR number

    PH27505

  • Reported component name

    WEBS APP SERV N

  • Reported component ID

    5724H8800

  • Reported release

    900

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2020-07-16

  • Closed date

    2020-10-15

  • Last modified date

    2020-10-15

  • 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

    WEBS APP SERV N

  • Fixed component ID

    5724H8800

Applicable component levels

[{"Line of Business":{"code":"LOB36","label":"IBM Automation"},"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Product":{"code":"SSEQTP","label":"WebSphere Application Server"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"900"}]

Document Information

Modified date:
16 October 2020