PH14488: IBM MQ V9 Z/OS: INCORRECT POSTING OF AC_SUSPENDECB WITH A POSTCODE OF 0 CAUSES A HIGH CPU

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Customer used MDB applications on zWAS in 2-way sysplex
  environment. An MQ MDB thread was consuming a lot of CPU in
  zWAS controller region. In that environment, they changed an MDB
  target queue as get(disabled) from one member (SYSTEM S1).
  Later zWAS CR on SYSTEM S1 started to consume a lot of CPU.
  The high CPU situation continued after that.
  
  IBM c/t lab now confirmed that the incorrect posting of
  AC_SuspendECB with a postcode of 0 can lead to a high
  cpu loop, and had recreated a scenario where this loop
  occurred.
  

Local fix

• n/a
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 1 Modification 0.                    *
  ****************************************************************
  * PROBLEM DESCRIPTION: 64 bit applications using asynchronous  *
  *                      consumption (MQCB/MQCTL), for example   *
  *                      MDBs,experience high cpu when the       *
  *                      consumer is suspended or stopped.       *
  ****************************************************************
  When a consumer task is posted to suspend and subsequently stop,
  an error occurs when posting the AC_ResumeECB causing it to
  be posted with an invalid postcode (either 0, or a residual
  suspend value).
  This postcode is unexpected, and causes the task requesting the
  consumer stops to loop.
  

Problem conclusion

• CSQBMCS2 is changed to prevent the residual postcode overriding
  the expected postcode when an MDB is requested to stop, and to
  pass the postcode correctly to CSQBMCSD when running in 64bit
  environments.
  

Temporary fix

Comments

APAR Information

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

  PH02556

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

  UI65102

Modules/Macros

• CSQBLB1  CSQBLB16 CSQBLB1X CSQBLB2  CSQBLB26 CSQBLB2X CSQBLB3
  CSQBLB36 CSQBLB3X CSQBLB46 CSQBLB4X CSQBLB56 CSQBLB5X
  

Fix information

• Fixed component name

  IBM MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R100 PSY UI65102

     UP19/09/26 P F909 ¢

Fix is available

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