PK84370: CROSS SYSTEM DEADLOCK WHEN USING CICS DISTRIBUTED PROGRAM LINK ( DPL ) WITH DBCTL AND FASTPATH DEDB

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Customer encountered a deadlock condition resulting in system
  hangs when using CICS DPL in a DBTCL threads that access DEDBs.
  The deadlock is as follows
  Global Tran X IMS A component -> Phase I. Obtains DBFSYNL latch
  SHR. Waits for Phase II call.
  Global Tran Y IMS B component -> Phase I. Obtains DBFSYNL latch
  SHR. Waits for Phase II call.
  IMS A system checkpoint or Area command requests DBFSYNL EXCL
  and must wait, due to SHR ownership by Global Tran X IMS A
  component.
  Same on IMSB, must wait due to SHR ownership by Global Tran Y
  IMS B component
  CICS drives Phase I for Global Tran X IMS B component. Since
  there is EXCL waitor for DBFSYNL on IMSB, wait.
  Phase II for Global Tran X IMS B component cannot be driven
  on IMS A until Phase I on IMS B is complete.
  CICS drives Phase I for Global Tran Y IMS A component. Since
  there is EXCL waitor for DBFSYNL on IMSA, wait
  Phase II for Global Tran Y IMS A component cannot be driven
  on IMS B until Phase I on IMS A is complete.
  Both IMS A and IMS B are now deadlocked. Since there is an
  EXCL requestor for DBFSYNL, any syncpoint request ( DBCTL
  or otherwise ) that needs FastPath processing must wait for
  DBFSYNL and such syncpoints now wait ( forever ).
  

Local fix

• It is possible to break the deadlock with a /STO REG ABDUMP
  command against either transaction. It can be very difficult,
  however, to identify the DBFSYNL owner. Also, this will cause
  the thread to become INDOUBT, and require resolution by
  /CHA CCTL command.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: IMSFP V10 DEDB DBCTL user with CICS          *
  *                 Distributed Program Link ( DPL )             *
  *                 2 phase transaction may be effected.         *
  ****************************************************************
  * PROBLEM DESCRIPTION: CROSS SYSTEM DEADLOCK WHEN USING CICS   *
  *                      DISTRIBUTED PROGRAM LINK ( DPL )        *
  *                      WITH DBCTL AND FASTPATH DEDB.           *
  ****************************************************************
  * RECOMMENDATION: INSTALL CORRECTIVE SERVICE FOR APAR/PTF      *
  ****************************************************************
  Customer encountered a deadlock condition resulting in system
  hangs when using CICS DPL in a DBTCL threads that access DEDBs.
  The deadlock is as follows
  Global Tran X IMS A component -> Phase I. Obtains DBFSYNL latch
  SHR. Waits for Phase II call.
  Global Tran Y IMS B component -> Phase I. Obtains DBFSYNL latch
  SHR. Waits for Phase II call.
  IMS A system checkpoint or Area command requests DBFSYNL EXCL
  and must wait, due to SHR ownership by Global Tran X IMS A
  component.
  Same on IMSB, must wait due to SHR ownership by Global Tran Y
  IMS B component
  CICS drives Phase I for Global Tran X IMS B component. Since
  there is EXCL waiter for DBFSYNL on IMSB, wait.
  Phase II for Global Tran X IMS B component cannot be driven
  on IMS A until Phase I on IMS B is complete.
  CICS drives Phase I for Global Tran Y IMS A component. Since
  there is EXCL waiter for DBFSYNL on IMSA, wait
  Phase II for Global Tran Y IMS A component cannot be driven
  on IMS B until Phase I on IMS A is complete.
  Both IMS A and IMS B are now deadlocked. Since there is an
  EXCL requestor for DBFSYNL, any syncpoint request ( DBCTL
  or otherwise ) that needs FastPath processing must wait for
  DBFSYNL and such syncpoints will now wait forever.
  

Problem conclusion

• GEN:
  KEYWORDS:
  
  *** END IMS KEYWORDS ***
  The following changes have been made to correct the reported
  problem:
  
  DBFEPST:  Add new flag EPSTR4_CICSDPL to indicate CICS DPL
            transaction.
  
  DBFSYNL0: Modify code to allow CICS DPL transaction to obtain
            the DBFSYNL latch in shared mode, even if there is
            exclusive waiter.
  
  This service serves as a preconditioning code only.  Affected
  users need to contact IMS support to enable the code.
  

Temporary fix

• *********
  * HIPER *
  *********
  

Comments

APAR Information

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

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

  PK85351 UK46385

Modules/Macros

• DBFEPST  DBFSYNL0
  

Fix information

• Fixed component name

  IMS V10

• Fixed component ID

  5635A0100

Applicable component levels

• R010 PSY UK46385

     UP09/05/14 P F905 Ž

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.