PH53151: DEADLY EMBRACE ON NQLOCK, XMLOCK AND DSITLOCK

APAR status

• Closed as program error.

Error description

• Three tasks were suspended in the region, and waiting for the
  lock. Looking at the lock manager, we can see:
  
  - Task 1 owns XMLOCK and waits for DSITLOCK
  - Task2 owns DSITLOCK and waits for NQLOCK
  - Task3 owns NQLOCK and waits for XMLOCK
  
  Therefore, the tasks deadly embraced, and the CICS region hangs
  up.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: Three tasks are waiting for locks       *
  *                      DSITLOCK, NQLOCK & XMLOCK in a          *
  *                      three-way deadly embrace. The CICS      *
  *                      region hangs.                           *
  ****************************************************************
  Three tasks were suspended in the region, each waiting for a
  different lock. Looking at the lock manager, we can see:
  
  - Task 1 owns XMLOCK and waits for DSITLOCK
  - Task2 owns DSITLOCK and waits for NQLOCK
  - Task3 owns NQLOCK and waits for XMLOCK
  
  Therefore, the tasks are in a deadly embrace, and the CICS
  region hangs.
  The XMLOCK is acquired before needed, and has contributed to
  this deadlock due to the rare timing issue.
  

Problem conclusion

• DFHXMTA has been changed to move the DFHDSITM call to before
  the XMLOCK is obtained by DFHXMTA. Thus the DFHDSITM call is
  made without the XMLOCK being held but the rest of the code is
  protected by the XMLOCK.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  PH53149

• APAR is sysrouted TO one or more of the following:

  UI91912

Modules/Macros

• DFHXMTA
  

Fix information

• Fixed component name

  CICS TS Z/OS V6

• Fixed component ID

  5655YA100

Applicable component levels

• R400 PSY UI91912

     UP23/05/23 P F305