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PH25576: MQ Z/OS: A SMALL STORAGE LEAK OCCURS IN SP0 WHEN A CLIENT CONNECTS TO A GROUP LISTENER AND IS REJECTED DUE TO MAXINST

A fix is available

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APAR status

  • Closed as program error.

Error description

  • A small storage leak occurs when a client channel connects to a
    group listener and is then rejected because the channel has
    reached its MAXINST value:
      CSQX489E Maximum instance limit limit exceeded, channel
               <channel-name> connection <conn-id>
    
    As part of the set-up of the channel connection, a 240 byte
    (xF0) area of storage is allocated to hold information about
    the shared channel status (XSCS control block). When the CHIN
    determines that the channel cannot start due to MAXINST, it
    frees the resources allocated for the channel, but it does not
    release the XSCS storage.
    
    The storage is in Subpool 0 Key 8 (SP0 KEY8 K8).
    

Local fix

  • N/A
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
    *                 Release 0 Modification 0, Release 1          *
    *                 Modification 0 and Release 2 Modification 0. *
    ****************************************************************
    * PROBLEM DESCRIPTION: If a shared channel is prevented from   *
    *                      starting due to exceeding MAXINST,      *
    *                      MAXINSTC or MAXCHL, then a 240 byte     *
    *                      memory leak may occur in the CHINIT.    *
    *                                                              *
    *                      This will be accompanied by messages    *
    *                      CSQX489E, CSQX490E and CSQX513E for     *
    *                      MAXINST, MAXINSTC and MAXCHL            *
    *                      respectively.                           *
    ****************************************************************
    When starting a shared channel, a shared status entry is written
    to DB2 to provides status information about the connection
    throughout the QSG. If the connection is ultimately rejected due
    to exceeding MAXINST, MAXINSTC or MAXCHL, then the shared status
    entry is subsequently deleted from DB2. The code then attempts
    to free the in-memory copy, but does this incorrectly resulting
    in the storage being leaked.
    

Problem conclusion

  • The faulty logic has been corrected to free the shared status
    entry correctly.
    

Temporary fix

Comments

APAR Information

  • APAR number

    PH25576

  • 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

    2020-05-19

  • Closed date

    2021-05-13

  • Last modified date

    2021-06-02

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

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

    UI75377 UI75379 UI75380

Modules/Macros

  • CMQXRMSA CSQXRMSS
    

Fix information

  • Fixed component name

    IBM MQ Z/OS V9

  • Fixed component ID

    5655MQ900

Applicable component levels

  • R000 PSY UI75380

       UP21/05/29 P F105 ¢

  • R100 PSY UI75379

       UP21/05/29 P F105 ¢

  • R200 PSY UI75377

       UP21/05/29 P F105 ¢

Fix is available

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Document Information

Modified date:
03 June 2021