PH53427: TCP CONNECTION USING SMCR OR SMCD RETURNS 0 ON SEND REQUEST CAUSING APPLICATION TO LOOP ISSUING SENDS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• An unknown error occurs in the SMC layer for a TCP connection
  using SMCR or SMCD.  The SMC layer of the connection becomes
  unusable.  The application issues a socket send request and
  receives a return code 0 indicating no bytes were sent.  The
  application is designed to loop issuing send requests and
  decrementing the return code until the residual count becomes 0.
  The return code of 0 instead of a -1 with an error code results
  in the application looping indefinitely.
  
  SYMPTOMS
  Application suddently consumed a lot of CPU
  
  VERIFICATION STEPS
  Dump of TCPIP will show the following exception records in the
  SYSTCPIP component trace
  !Send error - SMCL conn not foun
  !SMC_Send update failed
     write completed
        +0000  00000000
     SMC_errno
       +0000  0000008C
     SMC_errnojr
        +0000  745B0446
  
  KEYWORDS
  loop looping
  high cpu
  unresponsive
  stalled connection
  

Local fix

• Drop the TCP connection.
  Recycle the application.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All users of the IBM Communications Server for z/OS 2.4, 2.5 *
  * and 3.1 IP: SMC                                              *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * The caller application program goes into a loop after        *
  * issuing a send() API call and receiving a return value of 0. *
  * The application then loops                                   *
  * attempting to send all the data after subtracting the amount *
  * returned in return value.                                    *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Apply the PTF                                                *
  ****************************************************************
  An unknown error occurs in the SMC layer for a TCP connection
  using SMCR or SMCD.  The SMC layer of the connection becomes
  unusable.  The application issues a socket send request and
  receives a return code 0 indicating no bytes were sent.  The
  application is designed to loop issuing send requests and
  decrementing the return code until the residual count becomes 0.
  The return code of 0 instead of a -1 with an error code results
  in the application looping indefinitely.
  

Problem conclusion

• The TCP send routine, ezbtsfwr, has been updated to copy and
  return to the calling application
  the return and reason codes when the send request fails using
  SMC (SMCR or SMCD). The return
  value will also be set to -1. This will allow the calling
  application to terminate.
  

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:

  UI92080 UI92081 UI92082

Modules/Macros

• EZBTSFWR
  

Fix information

• Fixed component name

  TCP/IP MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R240 PSY UI92080

     UP23/08/04 P F308

• R250 PSY UI92081

     UP23/08/04 P F308

• R310 PSY UI92082

     UP23/08/04 P F308

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.