PQ72228: CSA STORAGE EXHAUSTION - UNUSED DUCB'S (DUAT'S) NOT BEING FREED

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• System experiences a growth in ECSA usage, eventually resulting
  in allocation failures and ABENDs with associated loss of
  function.  Examination of the allocations will show a large
  number of x'000F6000' byte areas in SP241K6 with the following
  pattern at the start:
      xxxxxxxx xxxxxxxx 000F5FF0 06F1009F  |..........¬0.1..|
      C4E4C3C2 01000002 xxxxxxxx xxxxxxxx  |DUCB............|
  
  Running a TCPIPCS LOCK report will not show any unusual
  serializations (if any at all).  A TCPIPCS DUAF report will
  show a large number of DUCBs that have ABENDed and are not in
  use.  The chains of free DUCBs will be relatively empty.
  
  Systems that experience CSA shortages as a result of this
  problem will have had numerous ABENDs of applications that use
  TCPIP services, especially those that have a large number of
  sockets open (such as the web server).
  
  Other Keywords:
    JRNODUAVAILABLE x'F6000' F6000
    SQA ESQA SP239 filled with LSSD and SSRB for TCPIP asid.
  

Local fix

• Taking measures to avoid repetitive ABENDs in TCPIP applications
  will reduce the impact of this problem.  Recycling the TCPIP
  address space will free the affected storage areas.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the Communications Server for   *
  *                 z/OS Version 1 Release 2 & 4 IP              *
  ****************************************************************
  * PROBLEM DESCRIPTION: Orphaned DUCBs result in SP241 K6       *
  *                      storage growth.                         *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The TCPIP recovery routine places DUCBs that have abended on an
  abend queue to delay reuse.  The DUCBs on the abend queue are
  staged on a wait queue half way through the delay cycle.  The
  DUCBs are then made reusable and placed on the available queue.
  The DUCBs on the abend and wait queue are examined periodically
  to ensure they are not corrupted. When the check_ducb routine
  is called with an input value of 2, the wait queue is set to
  zero.  Any DUCBs that were chained on the wait queue will be
  orphaned when this occurs.
  The DUCB contraction logic identifies DUATs that may be
  contracted based on the DUCBs represented by a DUAT being on
  the available queue.  DUCBs that have been orphaned from the
  wait queue will never be placed back onto the available queue,
  thus preventing the associated DUAT from being eligible for
  contractions.
  Storage growth in SP241 K6 may occur as the number of DUCBs
  that are orphaned increase.
  +-------------------------------------------------------------+
  + Please check our Communications Server for OS/390 homepages +
  + for common networking tips and fixes.  The URL for these    +
  + homepages can be found in Informational APAR II11334.       +
  +-------------------------------------------------------------+
  

Problem conclusion

• The check_ducb routine has been amended to preserve the
  contents of the wait queue.
  
  * Cross Reference between External and Internal Names
  

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:

  UQ75660 UQ75661

Modules/Macros

• EZBITSCU
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R120 PSY UQ75660

     UP03/04/24 P F304

• R140 PSY UQ75661

     UP03/04/24 P F304

Fix is available

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