IT39506: FDC with probe ID XC006001 with xcsFreeMemFn and XECS_I_PRIVATE_MEMORY_ERROR

APAR status

• Closed as program error.

Error description

• MQ queue manager generates a failure data capture (FDC) record
  with:
    probe:     XC006001
    component: xcsFreeMemFn
    error:     xecS_I_PRIVATE_MEMORY_ERROR
  
  In the detailed FFST backtrace it can be seen that during the
  call to ccxReceiveThreadCleanup, the memory is being double
  freed (in this case identified by memory address 0x01f474a0)...
  
  { ccxReceiveThreadCleanup
  -{ ccxPoolFree
  --{ xcsFreeMemFn
  Data: 0x00000000 0x02dd4ad0
  --} xcsFreeMemFn rc=OK
  --{ xcsFreeMemFn
  Data: 0x00000000 0x01f474a0			<<< FIRST FREE
  --} xcsFreeMemFn rc=OK
  ...
  ... < SEVERAL LINES OF TRACE ENTRIES REMOVED FOR CLARITY > ...
  ...
  ------} zstMQBACK rc=OK
  -----} MQBACK rc=OK
  ----} rriRollback rc=OK
  ----{ ccxStageFree
  -----{ xcsFreeMemFn
  Data: 0x00000000 0x01f474a0			<<< SECOND FREE
  ------{ xcsBuildDumpPtr						<<< ERROR
  IS TRAPPED
  

Local fix

Problem summary

• ****************************************************************
  USERS AFFECTED:
  MQ Client or Channel applications with SHARECONV >= 1, that may
  experience network interruptions.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  During cleanup processing whilst a client connection closes, an
  attempt to free a dangling pointer referencing fragmented
  message staging memory, that had already been freed caused MQ's
  internal memory checks to capture the condition with an FDC.
  
  Previous similar APARs IT34004 and IT36729 failed to identify
  the additional possible double freeing of a pointer in this code
  area.
  

Problem conclusion

• Additional logic has been added to erase the reference pointer
  when the memory block is freed.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.1 LTS   9.1.0.11
  v9.2 LTS   9.2.0.6
  v9.x CD    9.3.0.0
  
  The latest available maintenance can be obtained from
  'WebSphere MQ Recommended Fixes'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
  
  If the maintenance level is not yet available information on
  its planned availability can be found in 'WebSphere MQ
  Planned Maintenance Release Dates'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
  ---------------------------------------------------------------
  

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:

Fix information

• Fixed component name

  IBM MQ BASE MP

• Fixed component ID

  5724H7271

Applicable component levels