On Fri, Oct 28, 2011 at 11:29:34AM +1100, Lawrence Stewart wrote: > On 10/26/11 22:53, John Baldwin wrote: > > The assertion would be triggered when the next packet arrives (as I said > > above). Try modifying your debugging output to also log if the ACK is > > delayed. I suspect it is not delayed until the last one. (Pushing out an > > ACK will reset rcv_adv to be beyond rcv_nxt in tcp_output(), so in the case > > of an immediate ACK, rcv_nxt> rcv_adv is only a transient condition all > > under a single lock invocation so never visible to other consumers of the > > protocol control block.) If that is what you see, then that confirms what > > I guessed above and I will likely just remove the assertion in tcp_input() > > and patch the timewait code to handle this case. > > > > Pawel, have you been able to confirm John's hypothesis? [...]
Yeah, sorry. I moved the debug to the points where we drop the t_inpcb
lock and I still see rcv_nxt being greater than rcv_adv:
tcp_do_segment:2970 negative window: tp 0xfffffe00685ee3d0 rcv_nxt
1312878324 rcv_adv 1312878187
This is just before the INP_WUNLOCK(tp->t_inpcb) under 'check_delack'
label. I see this a lot (it was logged 545 times for 11 different tp
pointers during 24h period).
tcp_do_segment:3009 negative window: tp 0xfffffe005cfc6000 rcv_nxt
1442546453 rcv_adv 1442545722
This is just before calling tcp_output(). This one was logged 65 times
for 3 different tp pointers.
I placed a debug also after tcp_output() call, but it is not logged, so
once we return from tcp_output() everything is fine.
The panic would be triggered 115 times for 5 different tp pointers
during that time.
I write 'tp pointers' as I'm not 100% sure if the same pointer always
represents the same connection or if it is reused.
> [...] What I don't
> quite get is why we haven't had a lot more reports of this issue...
Maybe because my TCP/IP stack is heavly modified? ...not:)
No idea to be honest. Ask Ken to turn on INVARIANTS in 9.0-RC2 and we
will see:)
--
Pawel Jakub Dawidek http://www.wheelsystems.com
FreeBSD committer http://www.FreeBSD.org
Am I Evil? Yes, I Am! http://yomoli.com
pgpN4xRhoFGYE.pgp
Description: PGP signature
