PM64610: ABENDU0780 RC205 AND OSAM WAITLCT WHEN IBFCRD (READ I/O) LEFT ON

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• U0780 RC205 was issued because the subpool latch (DBBP) was held
  when the dependent region was abnormally terminated with U0474.
  The DBBP latch was obtained at LCTSRCH prior to calling STEALBFR
  and held throughout DFSDBH20 during the OSAM READ I/O.  We won't
  release this subpool latch until the READ I/O is completed and
  we return to DFSDBH10. Therefore, when the U0474 was allowed to
  terminate the ODBA thread, IMS was left holding the DBBP latch
  in exclusive mode.  Additionally, the READ I/O IN PROGRESS flag
  (IBFCRD) was left ON.  This led to the U0780 RC205 latch abend.
  The second symptom was several dependent regions waiting (WLCT)
  for use of the same buffer, but prevented because IBFCRD was ON.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All IMS V11 Full Function OSAM users.        *
  ****************************************************************
  * PROBLEM DESCRIPTION: IMS dependent regions hang in DFSDBH20  *
  *                      waiting for use of a buffer when the    *
  *                      dependent region that owned the buffer  *
  *                      abnormally terminated with the IBFCRD   *
  *                      on indicating that read I/O is in       *
  *                      progress.   Also, ABENDU0780 RC205      *
  *                      occurs when the dependent region        *
  *                      abnormally terminated while holding the *
  *                      DBBP (OSAM buffer subpool) latch.       *
  ****************************************************************
  * RECOMMENDATION: INSTALL CORRECTIVE SERVICE FOR APAR/PTF      *
  ****************************************************************
  If a dependent region that was in the middle of OSAM READ I/O in
  module DFSDBH20 abnormally terminates, other dependent regions
  waiting for the use of the same buffer will hang in DFSDBH20.
  When doing OSAM read I/O, flag IBFCRD is set to prevent any
  other regions from accessing the buffer until the read has
  completed.  When the read is completed, PSTBFHLD flag is set to
  indicate that the region holds the buffer.  If the region doing
  the read I/O terminates abnormally, because PSTBFHLD has not yet
  been set, DFSFXC50 does not call DFSDBH10 to release the buffer
  and post the waiting dependent regions to pass ownership of the
  buffer to the next waiting region.  When this occurs dependent
  regions hang and threads may hang, forcing the user to restart
  IMS.
  
  A second problem can also occur.  When the region is doing the
  read I/O and terminates abnormally, it could terminate while
  holding the OSAM buffer subpool latch ( DBBP latch ).  If this
  occurs, the next attempt to get the latch may encounter an
  ABENDU0780 RC205.
  

Problem conclusion

• The following modules have been modified to correct the reported
  problem:
  
  ************
  * DFSFXC50 *
  ************
  Code has been modified to call DFSDBH10 with PSTFNCTN = PSTRELLR
  when PSTBFHLD is set or when IBFCRD is set even when PSTBFHLD is
  not set.
  
  ************
  * DFSDBH10 *
  ************
  Code has been added to call routine MKEMPTY to mark the buffer
  empty and post any waiting dependent region on the IBFWPST chain
  currently waiting for the buffer when DFSDBH10 is called with
  PSTFNCTN = PSTRELLR, PSTBFHLD is not set, IBFCRD is set, and
  IBFPSTLR indicates that the terminating region is the region
  that owns the buffer.
  

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:

  PM69681 UK80880

Modules/Macros

• DFSDBH10 DFSFXC50
  

Fix information

• Fixed component name

  IMS V11

• Fixed component ID

  5635A0200

Applicable component levels

• R100 PSY UK80880

     UP12/08/10 P F208

Fix is available

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