PH33215: DFHDS0004 A POSSIBLE LOOP HAS BEEN DETECTED AT OFFSET X'FFFF' IN MODULE DFHDSTCB.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Since migrating to CICS/TS 5.6, CICS regions are getting the
  following message:
  
  DFHDS0004 A possible loop has been detected at
    offset X'FFFF' in module DFHDSTCB.
  
  This problem is specific to the way DFHKETIX handles its work.
  When a STIMERM interval elapses (250ms elapsed timed) CICS will
  run DFHKETIX under an IRB.
  
  This checks to see if the running task should be abend U999 for
  runaway. There is specific code to detect whether the TCB for
  the task has entered an MVS wait (partition exit).
  This would be performed by the default task for the TCB.
  
  If so then we do not want to reestablish a STIMERM to run
  DFHKETIX again in 250ms as this could cause thrashing on quiet
  systems where TCBs are often in MVS waits.
  If we detect this scenario, we avoid further STIMERMs and
  have CICS set a new STIMERM for DFHKETIX when the TCB
  eventually wakes up.
  
  However the codepath at 5.6 reset a flag when taking this path,
  which meant that a subsequent invocation of DFHKETIX would
  believe it needed to perform initialisation work for this task.
  
  Default tasks (the code that runs in DFHDSTCB "between" user
  transactions) should not be eligible for U999 runaway abends,
  and normally are not treated as having been initialized for
  runaway, meaning DFHKETIX would not be interested in them.
  Because of the flag being reset, a subsequent invocation
  of DFHKETIX is activating runaway detection for the default
  task, and if it incurs sufficient CPU usage, CICS will abend
  the task with a U999 abend (captured by CICS and handled as a
  DFHDS0004 "possible loop" abend). Raising the ICVR value would
  make the problem less likely to happen.
  
  Because of the flag being reset in this particular case,
  a subsequent invocation of DFHKETIX would activate runaway
  detection for the default task, and should it incur
  sufficient CPU usage, abend the task with a U999 abend
  (captured by CICS and handled as a DFHDS0004 "possible loop"
  abend).
  

Local fix

• N/A
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All.                                         *
  ****************************************************************
  * PROBLEM DESCRIPTION: Abend DFHDS0004 issued.                 *
  ****************************************************************
  DFHKETIX should not be runaway abended for the CICS 'default
  task' ( which runs as DFHDSTCB between USER transactions ).
  However, a path exists in DFHKETIX where runaway can be
  activated for it.  This may present as a U999 abend followed
  by a DFHDS0004 - a possible loop has been detected.
  

Problem conclusion

• DFHKETIX has been modified to prevent runaway activation for the
  CICS 'default task'.
  

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:

  UI73848

Modules/Macros

• DFHKETIX
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R300 PSY UI73848

     UP21/02/09 P F102 ¢

Fix is available

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