PH26488: DFHDS0001 ABEND CODE 0C4/AKEA OCCURRED IN DFHDSTCB R8 SHOULD POINT TO DFHXMTXN FOR TASK BUT IT WAS FREEMAINED

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Running CICS TS 5.3 you receive the following message and
  then the region crashes.
  
  DFHDS0001 applid An abend (code 0C4/AKEA) has occurred at
            offset X'0DF8' in module DFHDSTCB.
  
  A dump at the time of the program check showed the failing
  instruction was:
  
  9201 5041 | MVI X'41'(R5),X'01'
  
  R5 contained a bad value, causing the ABEND0C4.
  
  R5 was loaded from R2 which also contained the bad value.
  Backing up in the code found R2 was loaded from R8+130.
  R8 should be point to the task's DFHXMTxn - the transaction
  manager transaction control block, but the area did
  not have the correct eye catcher:   >dfhxmtxn
  at the beginning of it.
  
  Trace was active in this dump, and we were able to
  learn the transaction was actually in the process
  of terminating. Transaction manager- XM was cleaning up
  the task when it was suspended requesting the SMLOCK.
  ..
  This was after a time where it had already freemained the
  DFHXMTxn control block for the task.
  This allowed storage manager to free up the entire page of
  storage it belonged on, allowing another task to allocate
  the storage.
  
  When the terminating task was attempted to be resumed, DFHDSTCB
  referenced this DFHXMTxn address from the task's DTA
  control block, which still had a pointer to it, leading to
  program check since it no longer reflected a DFHXMTxn.
  
  Here are the modules in the kernel stack for the task in the
  process of terminating:
  NAME
  
  DFHKETA
  DFHDSKE
  DFHXMTA
  DFHXMLD
  DFHXMQD
  DELETE_INSTANCE
  DFHAPDN
  APDN_TRANDEF_NOTIFY
  FREE_TRANDEF_STG
  DFHSMGF
  SMLOCK_GET
  DFHLMLM
  LOCK
  LOCK_EXCLUSIVE
  ADD_TO_LOCK_QUEUE
  SUSPEND
  DFHDSSR
  POP_TASK
  Additional Symptoms: KIXREVRJL
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users                               *
  ****************************************************************
  * PROBLEM DESCRIPTION: DFHDS0001 abend 0C4 /AKEA in            *
  *                      DFHDSTCB.                               *
  ****************************************************************
  A transaction completed, and DFHXMTA was called to free the
  XMT storage for it. However, DFHXMTA did not clear the address
  of the XMT from the DTA, held in field DTA_XM_TKN.
    Having freemained the XMT, the transaction then continued and
  suspended on the SMLOCK within routine unlock_trandef_inline.
  This allowed another transaction to run. The storage that had
  been used for the XMT was reused for another subpool.
    When the first transaction was redispatched, DFHDSTCB ran and
  tried to update the WLM performance block, addressed from the
  XMT via the DTA. Since DTA_XM_TXN was not null, DFHDSTCB used
  this pointer to address what it believed was still a valid XMT.
  Since the DS_PB_TOKEN was not valid within the reused storage,
  this led to an 0C4/AKEA abend and CICS terminated.
  KEYWORDS: DSTCB PUSH_TASK
  

Problem conclusion

• DFHXMTA has been changed to clear DTA_XM_TXN when the XMTXN
  is freemained within free_transaction.
  

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:

  UI70741 UI70742 UI70743 UI70744

Modules/Macros

• DFHXMTA
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R000 PSY UI70741

     UP20/07/28 P F007 ¢

• R100 PSY UI70742

     UP20/07/25 P F007 ¢

• R200 PSY UI70744

     UP20/07/25 P F007 ¢

• R300 PSY UI70743

     UP20/07/25 P F007 ¢

Fix is available

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