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
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