PH34286: CORRECTS A DEADLOCK SITUATION, BETWEEN A CICS TCB, AND MQ END-OF-TASK PROCESSING

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When a CICS MQ connection is disabled, CSQCECTX schedules an
  IRB for each CICS TCB that is connected to MQ.
  At the same time, a CICS TCB may be ending. MQ's end-of-task
  routine, CSQ3EOT0 is invoked to disconnect the TCB from MQ.
  It is possible for the IRB to interrupt CSQ3EOT0's processing
  while it holds the AMGSLTCH latch.
  The IRB attempts to disconnect the TCB from MQ, which also
  requires the AMGSLTCH.
  This results in a deadlock, with the IRB waiting on the latch
  which is held by the code that it interrupted.
  This problem can also result in a TCB waiting indefinitely in
  CSQ3SSI2 while holding the 'CSQYALLI' resource. This will result
  in CICS shutdown hanging.
  
  This is a sister APAR to:  PH32757
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 1 Modification 0 and Release 2       *
  *                 Modification 0.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: When a CICS MQ connection is disabled,  *
  *                      an IRB is scheduled for each CICS TCB   *
  *                      that is connected to MQ. Concurrently,  *
  *                      a CICS TCB may be ending and the IRB    *
  *                      may interrupt this processing whilst    *
  *                      it is holding the latch. The IRB        *
  *                      attempts to disconnect, requiring the   *
  *                      latch. This results in a situation      *
  *                      where the TCB is deadlocked with        *
  *                      itself.                                 *
  ****************************************************************
  The code that attempts to to terminate the TCBs connection to
  MQ requires the latch, however the latch is already held so the
  AMGSLTCH latch request suspends from CSQ3EOT0 and the TCB
  becomes deadlocked with itself.
  

Problem conclusion

• The code has been changed to avoid a scenario where the TCB
  is deadlocked with itself.
  

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:

  UI77015 UI77167

Modules/Macros

• CSQCECTX CSQCEOTE
  

Fix information

• Fixed component name

  IBM MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R100 PSY UI77167

     UP21/09/29 P F109 ¢

• R200 PSY UI77015

     UP21/09/29 P F109 ¢

Fix is available

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