IBM Support

PQ06182: TCP/IP LOOP OR HIGH CPU USAGE FOR A WHILE

A fix is available

Subscribe

You can track all active APARs for this component.

 

APAR status

  • Closed as program error.

Error description

  • Loop occurred in EZACA03P(MVPVTAMP) VTMDIDIT routine(around offs
    et 49E) while processing VTRQ on GCBVQEL@ queue.  The VTRQ on
    GCBVQEL@ was already freed and on the Free_VTRQ chain.  More
    than 30000 VTRQs were on the Free_VTRQ queue and caused high
    CPU usage for half an hour.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All, Telnet users.                           *
    ****************************************************************
    * PROBLEM DESCRIPTION: A loop occurred in MVPVTAMP (VTMDIDIT)  *
    *                      while processing VTRQs on the GCBVQEL   *
    *                      queue.  The VTRQ was already freed and  *
    *                      on the Free_VTRQ chain.  When a VTRQ    *
    *                      for a Reply_Sent_Op_Code was dequeue    *
    *                      it brought with it more than 30,000     *
    *                      VTRQs resulting in high CPU usage.      *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
      The problem is timing related. While one procedure was in the
    process of dequeuing a work request(VTRQ), via a CS instruction.
    Another process was adding the VTRQ to the Freequeue chain.
    When this occurred all VTRQ's on the Free_Queue were moved by
    mistake to the GCBVQEL queue, thus causing the problem of
    running the long queue(loop). 90% of all VTRQs on the chain were
    for Reply_Sent_Op_Code requests.  There are two modules that
    can free the Reply_Sent VTRQs (MVPVIVSP and MVPVTAMP). Currently
    there is no way of knowing which module will free the request.
    Thus the possibility exists where, MVPVIVSP frees the request
    and the VTRQ may be re-used and placed on the top of the GCBVQEL
    LIFO queue.  When MVPVTAMP receives control it attempts to
    complete its processing of the original VTRQ by freeing it and
    placing it back on the free chain.
    

Problem conclusion

  • Modules MVPVTAMP(EZACA03P), MVPVIVSP(EZACA03s) and MVPVVECP
    (EZACA03T) were changed to verify if the VTRQ is on the VTRQ
    free chain before trying to use it.  The MVPVCOM control block
    was changed to add a new bit within the VTRQ mapping to indicate
    when the VTRQ is placed on the Free_Chain.
    
    * Cross Reference between External and Internal Names
    EZACA02S (MVPVIVSP)  EZACA03P (MVPVTAMP)  EZACA03T (MVPVVECP)
    EZADD01O (MVPVCOM )  EZACA02S (MVPVIVSP)  EZACA03P (MVPVTAMP)
    EZACA03T (MVPVVECP)  EZADD01O (MVPVCOM )
    

Temporary fix

Comments

APAR Information

  • APAR number

    PQ06182

  • Reported component name

    TCP/IP V3 MVS

  • Reported component ID

    5655HAL00

  • Reported release

    310

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    1997-07-07

  • Closed date

    1997-10-10

  • Last modified date

    1997-11-02

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

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

    UQ10229 UQ10230

Modules/Macros

  • EZACA02S EZACA03P EZACA03T EZADD01O
    

Fix information

  • Fixed component name

    TCP/IP V3 MVS

  • Fixed component ID

    5655HAL00

Applicable component levels

  • R310 PSY UQ10229

       UP97/10/31 P F710

  • R320 PSY UQ10230

       UP97/10/31 P F710

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.

[{"Business Unit":{"code":"BU054","label":"Systems w\/TPS"},"Product":{"code":"SG19M","label":"APARs - z\/OS environment"},"Component":"","ARM Category":[],"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"310","Edition":"","Line of Business":{"code":"","label":""}},{"Business Unit":{"code":"BU054","label":"Systems w\/TPS"},"Product":{"code":"SSCY4DZ","label":"DO NOT USE"},"Component":"","ARM Category":[],"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"310","Edition":"","Line of Business":{"code":"","label":""}}]

Document Information

Modified date:
02 November 1997