PH40702: WMQ ABN=0C4-00000011 CSQISLOG

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• MQ Development finds that the abend occurred in CSQISLOG when
  attempting to get a free ISLH control block from the ISLH QPHB.
  After loading the head of the freechain, the task was
  undispatched and in the interval where it was not dispatched
  storage contraction ran for this QPHB, freeing the extent
  containing the ISLH that had been at the head of the free
  chain. When the original task was redispatched it attempted to
  reference the ISLH as part of removing it from the freechain,
  and as the storage had now been freemained, this led to the
  reported abend.
  *
  Additional keywords:
  ABEND0C4 ABENDS0C4
  .
  ABN=0C4-00000011,C=MQ900.910.DMC -CSQISLOG,M=CSQGFRCV,
  LOC=CSQILPLM.CSQISLOG+00000584
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 1 Modification 0 and Release 2       *
  *                 Modification 0.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: A timing window exists where a task is  *
  *                      un-dispatched while getting storage for *
  *                      an ISLH control block, and local        *
  *                      storage compression subsequently        *
  *                      occurs. If storage compression frees    *
  *                      the underlying QuickCell block, then a  *
  *                      subsequent reference to the block by    *
  *                      the task may result in an ABEND0C4.     *
  ****************************************************************
  Free QuickCell blocks are maintained on a linked list free
  chain, and blocks are got and freed to the head of the chain. A
  timing window exists between reading the head pointer, and
  reading the block forward pointer. If the task is un-dispatched
  between reading the head pointer and reading the pointer to the
  next block on the chain, then the QuickCell block may be freed
  by storage compression before the task is re-dispatched. A
  subsequent attempt to read the pointer to the next block may
  result in an 0C4 abend.
  

Problem conclusion

• The logic for getting an ISLH has been changed to reduce the
  timing window.
  

Temporary fix

Comments

APAR Information

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

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

  UI78846 UI78847

Modules/Macros

• CSQILCHG CSQILINS CSQILVAL CSQIMPU2 CSQISLOG
  

Fix information

• Fixed component name

  IBM MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R100 PSY UI78847

     UP22/02/10 P F202

• R200 PSY UI78846

     UP22/02/10 P F202

Fix is available

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