A fix is available
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
IV13827
Reported component name
AIX 5.3
Reported component ID
5765G0300
Reported release
530
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Submitted date
2012-01-23
Closed date
2012-02-01
Last modified date
2013-04-13
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
Fix information
Fixed component name
AIX 5.3
Fixed component ID
5765G0300
Applicable component levels
R530 PSY U846347
UP12/04/18 I 1000
PTF to Fileset Mapping
U846347 bos.net.tcp.client 5.3.12.6
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Document Information
Modified date:
13 April 2013