PH44903: ABN=0C4-00000010,U=SYSOPR ,C=MQ900.9XX.ASMC-CSQVDISC,M=CSQVDISC,LOC=CSQVGEPL.CSQVDISC

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• ABEND0C4 occurred at CSQVDISC when removing the ACE from VLCA
  chain, but ACE address is x'C6D9C5C5' (FREE).
  
  The original problem was likely that an ACE was freed while
  still on a VLCAAACE chain, which may have been some time ago.
  There is no trace and the free ACE's SKB, which contains the
  stack storage, has been reused. The problem was only detected
  when the next time the VLCAAACE chain was ran.
  
  The abend may result in queue manager termination.
  
  This APAR is for diagnostic purposes so that IBM MQ
  Development: z/OS Service team can add extra diagnostics to
  earlier detect free ACE on VLCAAACE chains.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 1 Modification 0, Release 2          *
  *                 Modification 0 and Release 3 Modification 0. *
  ****************************************************************
  * PROBLEM DESCRIPTION: An MQ QMGR keeps track of active        *
  *                      threads by chaining ACE control blocks  *
  *                      onto VLCAAACE chains. If an ACE is      *
  *                      freed while on a VLCAAACE chain, then   *
  *                      this can lead to S0C4 abends or looping *
  *                      when running the chain.                 *
  ****************************************************************
  In the scenario where an ACE is freed while on a VLCAAACE chain,
  this can lead to S0C4 abends when running the chain because the
  chain address is EBCDIC 'FREE'. If the ACE is re-obtained and
  then chained to the same VLCAAACE chain, then this will result
  in the same ACE being on the chain twice, which will result in
  looping when running the chain.
  

Problem conclusion

• Diagnostic checks have been added to collect diagnostics if an
  ACE is freed while still on a VLCAAACE chain. If this scenario
  occurs, then an S5C6-00E50039 abend will occur and a dump will
  be taken. This APAR does not attempt to address the root cause
  of an ACE being freed while on a VLCAAACE chain.
  

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:

  UI93819 UI93820 UI93821

Modules/Macros

• CSQ3EC0X CSQ3ID30 CSQ3IDES CSQ3RRSF CSQ3RRSM CSQ3RRSX CSQAPRHX
  CSQARIB  CSQMCPRH CSQMCTXE CSQSCON2 CSQSFBK  CSQSFPL  CSQVCFRR
  CSQVCONN CSQVCRTH CSQVDISC CSQVGACE CSQVGEPL CSQVPDAC CSQVRMIM
  CSQVTFRR CSQVTRTH CSQVUTIL CSQYAGCS
  

Fix information

• Fixed component name

  IBM MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R100 PSY UI94294

     UP23/11/21 P F311 ¢

• R200 PSY UI94293

     UP23/11/16 P F311 ¢

• R300 PSY UI94292

     UP23/11/16 P F311 ¢

Fix is available

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