PH41022: ABEND0C4 IN DSNXERD ON A COMPARE INSTRUCTION ( 5910 F000 ) AT +X'286' LEADS TO ABENDAD2R

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Abend0C4 PIC11 on a Compare instruction ( 5910 F000  ) (   C
  R1,X'0'(,R15)  ) at +x'286' into DSNXERD because Reg15
  references a free page.
  
  The bottom half of Reg1 contains D7C24040 .
  The bottom half of Reg15 contains FD633B00.
  
  7D633B00 is supposed to be the address of a PB ( Performance
  Block).  The Compare instruction is validating that Reg15
  addresses a PB.  But 7D633B00 falls within a free page, causing
  the 0C4-11.
  
  This program check results in transaction abend AD2R abendAD2R .
  
  
  7D633B00 is the address of the PB that was used by the prior
  transaction to use this thread.  That PB was freed when that
  transaction ended.  The current transaction using this thread
  has a different PB.
  
  When a connection/thread is IDENtified to Db2, CICS passes to
  Db2 the address of csb_wlm_perf_token ( CSB +x'DC').  As
  multiple transactions use this thread, one at a time, Db2
  reloads the current PB from csb_wlm_perf_token when CICS calls
  Db2 to ASSOciate a new transaction to the thread.  But CICS is
  populating csb_wlm_perf_token with a new transaction's PB
  *after* calling Db2 for ASSOciate.  That is why Db2 uses the PB
  that belonged to the prior transaction.
  
  Getting the 0C4 in DSNXERD does not usually happen because CICS
  does not usually freemain a PB at the end of the transaction.
  CICS freemains the PB and the end of the transaction when there
  was a problem during CICS initialization that leaves the WLM
  Free Performance Block Array uninitialized. To check that in a
  dump of CICS, do verbx dfhpd730 'MN=3' and find on MNFPBA.  If
  the array is all binary zeroes and below that you see Current XM
  Notified MXT Value =     0, then this region had a problem
  during initialization and will be freemaining PBs at the end of
  each transaction.
  

Local fix

• Do CEMT INQ SYSTEM and scroll down to see MAXTASKS.  Overtype
  the MAXTASKS value to make it one more or one less than it is.
  That should cause the WLM PB Array to be initialized, and that
  should cause CICS to quit freeing PBs at the end of each
  transaction, and that should cause the 0C4 in DSNXERD to stop.
  You can put the MAXTASKS value back to what it was if you want.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS Users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: Abend 0C4 in DSNXERD and Abend AD2R in  *
  *                      CICS.                                   *
  ****************************************************************
  It is possible for a CICS Db2 transaction to issue a GETMAIN for
  a  WLM Performance Block. At transaction end the WLM PB is
  freed.
  However a field in the CSUB, csb_wlm_perf_token, still
  references the freed WLM PB and not the newly GETMAINed WLM PB.
  This freed WLM PB will now be used by Db2 to set up this
  connection.
  Using the freed WLM PB causes Db2 to abend 0C4 in DSNXERD and
  for CICS to take an AD2R.
  

Problem conclusion

• DFHD2D2 has been changed to use the correct WLM Performance
  Block for each 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:

  UI78227

Modules/Macros

• DFHD2D2
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R300 PSY UI78227

     UP21/11/24 P F111

Fix is available

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