IV13751: ASSERT IN TCP_OUTPUT DUE TO VERY SMALL MSS APPLIES TO AIX 6100-05

A fix is available

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You can track all active APARs for this component.

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

    IV13751

  • Reported component name

    AIX 610 STD EDI

  • Reported component ID

    5765G6200

  • Reported release

    610

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Submitted date

    2012-01-20

  • Closed date

    2012-01-30

  • Last modified date

    2013-04-13

Fix information

  • Fixed component name

    AIX 610 STD EDI

  • Fixed component ID

    5765G6200

Applicable component levels

  • R610 PSY U849815

       UP12/04/18 I 1000

PTF to Fileset Mapping



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Document information


More support for:

AIX Enterprise Edition

Software version:

610

Operating system(s):

AIX

Reference #:

IV13751

Modified date:

2013-04-13

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