PM14602: TCP/IP LOOPING IN IUTLLCDQ

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• TCP/IP loops in IUTLLCDQ after a force,arm was issued to
  terminate the address space. The loop occurs while tcpip tasks
  are dispatchable in task termination and inbound packets arrive
  from OSA. Vtam schedules SRB in TCPIP, the SRB is retruned to
  VTAM, but enough inbound SRB work caused TCPIP task related
  termination processing to be overwhelmed by this work. This
  caused TCPIP task level processing related to notifying VTAM
  that termination is occuring to not be done, thus the loop
  processing inbound SRB work.
  
  NOTE that force,arm is not the normal method of stopping TCP/IP,
  for most normal cases use the stop command.
  

Local fix

• once the loop is detected after the force,arm issue a force
  command to terminate TCPIP.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications Server   *
  *                 for z/OS Version 1 Release(s) 11 and 12 IP   *
  ****************************************************************
  * PROBLEM DESCRIPTION: TCPIP looping in IUTLLCDQ following     *
  *                      a FORCE,ARM                             *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  TCPIP looping in IUTLLCDQ following a FORCE,ARM to terminate the
  address space.
  Recovery processing is driven for the FORCE,ARM and TCPIP sets a
  control flag that rejects new units of work entering the main
  code path.  If VTAM schedules an SRB into IUTLLCDQ to process
  inbound packets from an OSA device, TCPIP will reject the
  request and set an indicator that causes IUTLLCDQ to schedule a
  new SRB.  The newly scheduled SRB will get rejected in the same
  manner causing a new SRB to be scheduled.  This loop will
  continue until the TCPIP address space goes through memory
  termination.
  The number of looping SRBs is related to the number of active
  OSA devices with inbound data packets.  The TCPIP address
  space may never terminate if the number of looping SRBs exceeds
  the general purpose CPs defined to the LPAR.  The SRB mode work
  is dispatched prior to the task mode work which can prevent task
  level recovery processing and termination from completing.
  Issuing a FORCE command without the ARM parameter makes the
  address space non-dispatchable and immediately terminates the
  loop.
  +-------------------------------------------------------------+
  + 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

• EZBIFRC0 has been amended to set an indicator when the TCP/IP
  stack is terminating so that IUTLLCDQ does not schedule a new
  SRB to continue the initial work request.
  
  * 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:

  UK57424 UK57425

Modules/Macros

•    EZBIFRC0
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R1B0 PSY UK57424

     UP10/07/02 P F007

• R1C0 PSY UK57425

     UP10/07/02 P F007

Fix is available

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