odd TCP rtt/retransmit timeout issue...

[John-Mark Gurney]

Dan Nelson wrote this message on Mon, Sep 25, 2006 at 10:46 -0500:
> In the last episode (Sep 25), John-Mark Gurney said:
> > I was brining up another interface that I just added to /etc/rc.conf
> > and ran the command /etc/rc.d/netif start to initalize it...  But
> > then my connection never came back.... I found that the shell was
> > still active as I could type commands like sleep 5, and another
> > session's w would see sleep 5 run on the session...  even filling up
> > the send-q w/ 32k of data didn't get the HEAD box to send any data to
> > the client...
> > 
> > With the help of silby, I managed to find that the t_rxtcur value in
> > the tcpcb was getting a very large value.  The session that hung had
> > a retransmit timeout of 19 days...  This led us to find that the
> > TCPT_RANGESET macro was letting very large tvmin values override the
> > more sane tvmax values due to an extra else.  I have added that so we
> > shouldn't see any more multi day timeouts, but we still apparently
> > have a problem where the rtt value calculated is wildly incorrect...
> > 
> > It appears that each connection will get a different "random" rtt
> > values...  From a few connections to my machine:
> > (kgdb) print ((struct tcpcb *)0xc3a34af8)->t_rxtcur
> > $3 = 64000
> > (kgdb) print ((struct tcpcb *)0xc3a3457c)->t_rxtcur
> > $6 = 1662654093
> > (kgdb) print ((struct tcpcb *)0xc3a343a8)->t_rxtcur
> > $12 = 1358
> > (kgdb) print ((struct tcpcb *)0xc3a9e1d4)->t_rxtcur
> > $17 = 203
> > (kgdb) print ((struct tcpcb *)0xc3a9e000)->t_rxtcur
> > $19 = 284155863
> 
> Do you have net.inet.tcp.inflight.enable=1 ?  You might be hitting

Yes.

> something related to kern/75122.  You'll want to pull the raw gnats
> repository file to read it; the query-pr.cgi web interface doesn't
> parse the file right and it loses all the replies.

Doesn't look like it... I just disabled inflight, and my first connection
got:
(kgdb) print ((struct tcpcb *)0xc3a4857c)->t_rxtcur 
$1 = 921479340

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."