IT43696: Hang when MQ on AIX tries to write out the call stack after a heap-corruption SIGSEGV

APAR status

• Closed as program error.

Error description

• The hang that followed the SIGSEGV was due to MQ calling AIX
  service function mt__trce() to write out the call stack.
  
  This service function calls pthread_suspend_others_np, which
  itself calls malloc, and this is an unsafe call within an
  exception handler, because the heap might be corrupt.
  

Local fix

Problem summary

• ****************************************************************
  USERS AFFECTED:
  This only affects users running MQ on AIX in the extremely rare
  scenario where there has been corruption in the C runtime heap,
  resulting in a SIGSEGV exception that is handled by MQ's
  exception handler.
  
  
  Platforms affected:
  AIX
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  The AIX service function mt__trce() must not be used from an
  exception handler.
  

Problem conclusion

• The MQ code has been corrected on AIX, to avoid calling the
  service function mt__trce() from an exception handler.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.2 LTS   9.2.0.30
  v9.3 LTS   9.3.0.25
  v9.4 LTS   9.4.0.5
  v9.x CD    9.4.1
  
  The latest available maintenance can be obtained from
  'IBM MQ Recommended Fixes'
  https://www.ibm.com/support/pages/recommended-fixes-ibm-mq
  
  If the maintenance level is not yet available information on
  its planned availability can be found in 'IBM MQ
  Planned Maintenance Release Dates'
  https://ibm.biz/mqplannedmaintenance
  
  ---------------------------------------------------------------
  

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

  MQ BASE V9.2

• Fixed component ID

  5724H7281

Applicable component levels