PI92770: CICS REGION USING LIBERTY JVM CAN GET INTO A TIGHT LOOP SCANNING THE FREE T8 TCB CHAIN

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• You are running CICS Transaction server 5.3, using Liberty JVMs
  and notice the region becomes unresponsive.  A dump taken
  at this time shows the CICS QR TCB is in a tight loop in module
  DFHDSAT.  The loop is in code that is running down the chain of
  free open TCBs.  The occurs because a T8 TCB has been placed on
  the free chain twice.
  
  Additional Symptom(s) Search Keyword(s): KIXREVPAD
  hang hung high cpu FIND_VICTIM_DSTCB OPEN TCB
  May also see following symptoms:
  DFHDS0004 A possible loop has been detected at
            offset x'FFFF'in module DFHDSDS4.
  Loop occurs in a Java task, in module DFHDSDS4,
  routine ASSOCIATE_OPEN processing a CHANGE_MODE
  request.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: CICS may issue message DFHDS0004        *
  *                      and/or enter a tight loop under the     *
  *                      QR TCB.                                 *
  ****************************************************************
  When a pthread TCB (such as a T8) is created, it is possible
  that the tcb_address in the DS_TCB is not filled in. This
  occurs due to a concurrency race between the new thread and
  the thread which caused it to be attached.
  This corruption to the expected state of the DS_TCB can
  cause a Liberty servlet running on that TCB to prematurely
  release the T8 TCB and place its DS_TCB on the free chain
  for T8 TCBs (FREE_OPEN_BASESPACE_DS_TCBS).
  If the Liberty thread then terminates and releases the
  T8, it can be placed onto the free chain a second time,
  thereby creating a loop in the chain.
  Other processes in CICS attempting to remove a specific
  element from the chain may then enter a loop searching
  for the target element. This causes the TCB processing the
  chain (e.g. the QR TCB) to loop running a procedure
  such as ALLOCATE_OPEN, FIND_LRU_FREE_TCB, or
  TCB_POOL_MANAGEMENT.
  
  Additional keywords:
  msgDFHDS0004  DS0004
  

Problem conclusion

• DFHDSIT has been updated to avoid the race condition which
  led to the initial corruption of the DS_TCB. This ensures
  that the TCB_ADDRESS field is set correctly for new pthreads.
  

Temporary fix

Comments

• ×**** PE18/07/30 FIX IN ERROR. SEE APAR PH00938  FOR DESCRIPTION
  

APAR Information

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

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

  UI53791 UI53792

Modules/Macros

• DFHAPLJP DFHDSIT
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R000 PSY UI53791

     UP18/02/13 P F802 ¢

• R100 PSY UI53792

     UP18/02/13 P F802 ¢

Fix is available

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