PQ63152: TCPIP APPEARS HUNG AND DOES NOT ACCEPT COMMANDS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Customer experienced a hang condition in TCP/IP and did not
  accept any commands.
  CSM storage was constrained and EZBTCSND issued an unconditional
  storage request while holding the TCB lock.  Since storage
  was not available the task went into a wait on storage and
  continued to hold the lock.  Command processing needed the
  same lock and was suspended waiting for the lock to be freed.
  Verification Steps:
  1) Run TCPIPCS report and CSM Fixed will be CRITICAL
  2) Run the TCPIPCS LOCK report
     Look for a DUCB holding a TCB lock exclusive and for
     another DUCB waiting for the same TCB
  3) Run TCPIPCS DUAF report and the DUCB holding the TCB lock
     will have a module flow including EZBTCSND, EZBITSMT,
     EZBITSCS, and EZBITDSS.
  ADDITIONAL SYMPTOMS:
  

Local fix

• KEYWORDS: HANG NETSTAT CSM CRITICAL
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications Server   *
  *                 for z/OS Version 1 Release 4 IP              *
  ****************************************************************
  * PROBLEM DESCRIPTION: TCPIP stopped processing commands.  An  *
  *                      unconditional storage request was made  *
  *                      for CSM managed ECSA while holding the  *
  *                      TCB lock.  The storage request could    *
  *                      not be satisfied so the unit of work    *
  *                      was suspended.  A connection table      *
  *                      request was issued and was suspended    *
  *                      for the TCB lock while holding the IE   *
  *                      lock.                                   *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  An ECSA shortage occurred as a result of another problem.  TCP
  attempted to build an outbound packet with a send_reason of
  NEWDATA.  An unconditional ?skdki was issued to get the M_PROTO
  storage.  This request hung waiting on ECSA to become available
  while holding the TCB lock.
  A netstat command was issued that waited on the TCB lock while
  holding the IE lock.  Command processing stopped working at
  this point due to the IE lock being held by the DUCB waiting on
  the TCB lock.
  +-------------------------------------------------------------+
  + 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 storage request for the M_PROTO will be issued conditionally
  for outbound TCP packets.
  
  * Cross Reference between External and Internal Names
  

Temporary fix

Comments

APAR Information

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

  PQ60159

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

  UQ68432

Modules/Macros

• EZBTCFWR EZBTCSND TCSNDINT
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R140 PSY UQ68432

     UP02/08/20 P F208

Fix is available

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