PI85691: WMQ 900 RESILIENCY IMPROVEMENT TO DETECT LOOPING WITHIN STORAGEMANAGEMENT FOR MQ

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• WMQ 900 RESILIENCY IMPROVEMENT TO DETECT LOOPING WITHIN
  STORAGE MANAGEMENT for MQ
  .
  Additional Symptom(s) Search Keyword(s):
  Csect CSQSCON2 Lmod CSQSLD1 storage contraction loop
  Performance High CPU
  Thread 006.SMFACL02 SMFACL02 Latch SMCPVT SMCPHB
  Other threads hang hung hanging wait waiting
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 0 Modification 0.                    *
  ****************************************************************
  * PROBLEM DESCRIPTION: Following an overlay of MQ owned common *
  *                      storage, CSQSCON2 loops running a SHB   *
  *                      chain while holding the PHB latch.      *
  *                      As the latch is never released, this    *
  *                      causes other MQ tasks to hang waiting   *
  *                      on the latch, leading to application    *
  *                      hangs and timeouts.                     *
  ****************************************************************
  An overlay of MQ owned common storage occurred due to an error
  in another product/application running on the same system,
  leading to a loop being introduced in one of MQ's SHB chains for
  control blocks in common storage.
  
  When storage contraction was invoked (this occurs every 10
  minutes for common storage) to free any ECSA no longer required
  by the queue manager, CSQSCON2 obtained the PHB latch, and
  evaluated each SHB for control blocks in common storage.
  While evaluating the overlaid SHB, the loop that the overlay
  had introduced resulted in CSQSCON2 looping continually while
  still holding the latch.
  As this latch is commonly required by other MQ tasks (both
  internal, and for applications connected to MQ), this
  resulted in MQ and application hangs and timeouts occurring.
  This continued until the queue manager was identified as the
  source of the hanging tasks and canceled by an operator.
  

Problem conclusion

• CSQSCON2 is changed to be more resilient to storage overlays
  that would currently cause indefinite loops. While contracting
  storage, CSQSCON2 will now detect chains that are looping, and
  if found, will terminate the queue manager with REASON=00E2000E.
  

Temporary fix

Comments

APAR Information

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

  PI85379

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

  UI50701

Modules/Macros

• CSQSCON2
  

Fix information

• Fixed component name

  MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R000 PSY UI50701

     UP17/10/12 P F710 ¢

Fix is available

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