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IV14211: ASSERT IN TCP_OUTPUT DUE TO VERY SMALL MSS APPLIES TO AIX 7100-01

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APAR status

  • Closed as program error.

Error description

  • When the tcp maxseg (t_maxseg) goes below 6 and largesend
is
enabled, system would assert in tcp_output.
By default mss is 1460, but due to pmtu discovery if the
mtu
drops to 68, it is possible to have a low mss.

The stack would be similar to,
0)> f
pvthread+281400 STACK:
[0494F7A8]tcp_output+0019C8 (0000000000000008 [??])
[0494C870]tcp_usrreq+001550 (??, ??, ??, ??, ??)
[00474D18]soesend+001738 (??, ??, ??, ??, ??, ??, ??)
[0048E43C]_esend+0004DC (??, ??, ??, ??, ??)
[00003850]ovlya_addr_sc_flih_main+000130 ()
[kdb_get_virtual_memory] no real storage @ 319EC298
[D022E7CC]D022E7CC ()
[kdb_read_mem] no real storage @ FFFFFFFFFFF93D0

Local fix

  • The assert will be modified to have a graceful behavior
and care will be taken to avoid very small mss due to any
possible code flaws.

Problem summary

  • When the tcp maxseg (t_maxseg) goes below 6 and largesend
is enabled, system would assert in tcp_output.
By default mss is 1460, but due to pmtu discovery if the
mtu drops to 68, it is possible to have a low mss.

The stack would be similar to,
0)> f
pvthread+281400 STACK:
 0494F7A8 tcp_output+0019C8 (0000000000000008  ?? )
 0494C870 tcp_usrreq+001550 (??, ??, ??, ??, ??)
 00474D18 soesend+001738 (??, ??, ??, ??, ??, ??, ??)
 0048E43C _esend+0004DC (??, ??, ??, ??, ??)
 00003850 ovlya_addr_sc_flih_main+000130 ()
 kdb_get_virtual_memory  no real storage @ 319EC298
 D022E7CC D022E7CC ()
 kdb_read_mem  no real storage @ FFFFFFFFFFF93D0

Problem conclusion

  • The assert will be modified to have a graceful behavior
and care will be taken to avoid very small mss due to any
possible code flaws.

Temporary fix

  • 



Comments


    

  • 



APAR Information




    

  • APAR number
    IV14211
    • 

  • Reported component name
    AIX V7.1
    • 

  • Reported component ID
    5765H4000
    • 

  • Reported release
    710
    • 

  • Status
    CLOSED  PER
    • 

  • PE
    NoPE
    • 

  • HIPER
    NoHIPER
    • 

  • Submitted date
    2012-01-26
    • 

  • Closed date
    2012-02-01
    • 

  • Last modified date
    2013-04-13
    • 





    

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

    
IV13751
    

    • 

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

    • 



Fix information


    

  • Fixed component name
    AIX V7.1
    • 

  • Fixed component ID
    5765H4000
    • 



Applicable component levels


    

  • R710  PSY  U843468
       UP12/05/11  I  1000
    • 



PTF to Fileset Mapping








      
              
                            

              

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Document Information


            

            


                        

            Modified date:
            

            13 April 2013
            

            
                      

        


        

        


      

    

  



    

  

  
    
            

          
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