PH58961: CICS DEADLOCK BETWEEN 2 TASKS FOR THE XMLOCK AND DUSYSDMP LOCK. TASKS IN LMQUEUE SUSPENDS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Hung CICS regions due to a deadlock with tasks hung in LMQUEUE
  suspends. There is a deadlock between 2 tasks waiting on the
  XMLOCK and DUSYSDMP locks.
  
  A CEMT task is processing a SET SYDUMPCODE(xxxxxx) REMOVE
  request and owns the system dump dataset lock, DUSYSDMP. The
  task is trying to issue message DFHDU0106 DUMPCODE xxxxxx has
  been discarded. This causes module DFHXMIQM to need the XMLOCK,
  but the task has to wait because the TCP task owns it.
  
  The TCP task is attaching a user task and owns the XMLOCK.
  TCP is trying to put out a DFHXM0212 message for the new
  transaction since the transaction was defined with an unknown
  TCLASS.
  
  DFHXM0212 Transaction TTTT has been attached with unknown
  TRANCLASS TCLASS.
  
  But the call to DFHMEME causes TCP to try to get the DUSYSDMP
  lock which is owned by CEMT, so the deadlock occurs. Other tasks
  then back up in LMQUEUE suspends.
  

Local fix

• Define and install the needed TCLASS definition.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: CEMT or EXEC CICS SET SYDUMPCODE        *
  *                      can cause CICS to stall with two        *
  *                      tasks in a deadly embrace.              *
  ****************************************************************
  A CICS task is processing CEMT or EXEC CICS SET SYDUMPCODE when
  another task causes a message to be issued.
  CICS suffers a locking problem between the two tasks.
  Each task contends for the XMLOCK and DUSYSDMP locks.
  The CICS tasks stall in SUSPENDs for the locks.
  If a dump is taken then it will show two tasks in a deadly
  embrace. One of then will have issued a SET SYDUMPCODE
  command.
  

Problem conclusion

• CICS SET SYDUMPCODE processing has been changed to prevent the
  need for the XMLOCK to be used.
  

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:

  UI96196

Modules/Macros

• DFHDUTM
  

Fix information

• Fixed component name

  CICS TS Z/OS V6

• Fixed component ID

  5655YA100

Applicable component levels

• R400 PSY UI96196

     UP24/03/23 P F403

Fix is available

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