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PH19716: Abend S0C4 in IGVCPOOL when called from CSQPMTRM

A fix is available

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APAR status

  • Closed as program error.

Error description

  • MSTR goes down intermittently due to abend 0C4-11 in IGVCPOOL.
    
    The error relates to MQ attempting to free storage in a z/OS
    cell pool.
    
    From the registers at the time of the abend, the z/OS function
    receives the 0C4 because the value it is using for the cellpool
    ID is invalid (in each case, the error value is x80000000). The
    Cell pool ID is passed by the calling MQ module, so from the
    z/OS perspective it looks like MQ has passed an invalid value
    for the cell pool ID.
    
    In the dump, however, the control blocks that MQ would have
    used to establish the cellpool ID all look valid, and the ID
    value is correct, so it is not clear where the bad value came
    from or how it ended up being used.
    
    The dump gotten is not captured at the time of the original
    0C4, so analysis of the contents is subject to the possibility
    that the content may have changed between the 0C4 and the dump
    being captured.
    
    The issue occurs in logic which is performing I/O to pagesets.
    This means it is likely to be related to the profile of work
    being done.
    
    The qmgr seeing the error was being used for QREP processing.
    This drives a particularly heavy usage pattern on individual
    queues, and also tends to drive read-ahead of pages from the
    pageset.
    
    The problem appears to be highly intermittent, it is likely to
    be a timing issue and the current evidence suggests that the
    necessary conditions are more likely to occur with the QREP
    workload.
    
    An alternative implementation could be written which would not
    require cell pools for the problem code. This logic change was
    made in the MQ V9.1 version, which removes the failing cell
    pool call and avoids the possibility of this abend occurring.
    
    This APAR was raised to investigate the feasibility of
    back-porting the V9.1 logic to V9.0.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
    *                 Release 0 Modification 0                     *
    ****************************************************************
    * PROBLEM DESCRIPTION: Abend 0C4 occurs in cpool processing    *
    *                      (IGVCPOOL) due to an invalid cpoolid    *
    *                      being passed by CSQPMTRM.               *
    *                      The abend is followed by abnormal       *
    *                      queue manager termination 6C6.          *
    ****************************************************************
    When an IO request to read a page due to readahead processing
    completes, and the buffer is above the bar, and pageable,
    CSQPMTRM calls IARV64 to unfix the buffer. As part of this
    processing storage is obtained from and freed to a CPOOL.
    An error in locating the cpool id can result in an invalid
    id being passed to CPOOL under certain timing conditions,
    resulting in the reported abend.
    

Problem conclusion

  • CSQPMTRM is changed to locate the cpool id correctly.
    

Temporary fix

Comments

APAR Information

  • APAR number

    PH19716

  • Reported component name

    IBM MQ Z/OS V9

  • Reported component ID

    5655MQ900

  • Reported release

    000

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2019-11-27

  • Closed date

    2020-01-03

  • Last modified date

    2020-02-04

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

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

    UI67227

Modules/Macros

  • CSQPMTRM
    

Fix information

  • Fixed component name

    IBM MQ Z/OS V9

  • Fixed component ID

    5655MQ900

Applicable component levels

  • R000 PSY UI67227

       UP20/01/25 P F001 ¢

Fix is available

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Document Information

Modified date:
04 February 2020