9.0-RC1 panic in tcp_input: negative winow.

[John Baldwin]

On Thursday, December 29, 2011 3:25:02 pm Pawel Jakub Dawidek wrote:
> On Thu, Dec 29, 2011 at 11:12:59AM -0500, John Baldwin wrote:
> > On Sunday, December 25, 2011 11:01:33 am Коньков Евгений wrote:
> > > Здравствуйте, John.
> > > 
> > > Вы писали 20 декабря 2011 г., 16:52:44:
> > > 
> > > JB> On Saturday, December 17, 2011 6:21:27 pm Pawel Jakub Dawidek wrote:
> > > >> On Mon, Dec 12, 2011 at 11:00:23AM -0500, John Baldwin wrote:
> > > >> > An update.  I've sent Pawel a testing patch to see if my hypothesis is correct
> > > >> > (www.freebsd.org/~jhb/patches/tcp_negwin_test.patch).  If it is then I intend
> > > >> > to commit www.freebsd.org/~jhb/patches/tcp_negwin2.patch as the fix.
> > > >> 
> > > >> Unfortunately it paniced today. Take a look at:
> > > >> 
> > > >>       http://people.freebsd.org/~pjd/misc/tcp_panic.jpg
> > > 
> > > JB> Ok, the one use case I was worried about is happening regularly before your
> > > JB> panic, so that is good.  Can you use gdb to figure out which call to
> > > JB> tcp_output() is actually panic'ing?  I wonder if it is this case:
> > > 
> > > JB>         /*
> > > JB>          * Return any desired output.
> > > JB>          */
> > > JB>         if (needoutput || (tp->t_flags & TF_ACKNOW)) {
> > > JB>                 (void) tcp_output(tp);
> > > JB>                 /* XXX: Debug */
> > > JB>                 KASSERT(SEQ_GEQ(tp->rcv_adv, tp->rcv_nxt),
> > > JB>                     ("tcp_input: negative window after ACK"));
> > > 
> > > JB> And if 'needoutput' is true, but TF_ACKNOW is not set, and tcp_output() decides
> > > JB> to not do anything.  I've updated tcp_negwin_test.patch to not panic if that call
> > > JB> to tcp_output() doesn't actually send a packet.  Please re-test.
> > > 
> > > 
> > > # uname -a
> > > FreeBSD meta-up 9.0-PRERELEASE FreeBSD 9.0-PRERELEASE #4: Sat Dec 24 13:59:20 EET 2011     @:/usr/obj/usr/src/sys/KES_KERN_v10  i386
> > > 
> > > rebooting once per day. Now I compile kernel with debug options.
> > > Can you advice me which and where I find debug info when it will
> > > reboting next time? so I can help to debug problem
> > 
> > Are you using the patch at the URL above (tcp_negwin_test.patch)?  If not,
> > can you try applying that patch and seeing if you still get any panics?
> 
> I applied 1.5 days ago, so far now panics and no other messages.
> I modified the patch a bit to not panic, but print a message when panic
> was suppose to happen. This box is too valuable for me to panic it too
> often. Because there were no debug messages I understand that the
> scenerio didn't happen yet and not that the problem is fixed, right?

Yes.  It would be best to see the messages logged to be safe.  Thanks.

-- 
John Baldwin