On Saturday, May 14, 2011 1:07:18 pm Mikolaj Golub wrote:
>
> On Sat, 14 May 2011 10:37:51 -0400 John Baldwin wrote:
>
> JB> Can you capture a tcpdump (probably easiest to do from the other host)?
>
> I replaced the asserts with log statements to make the host not panic and the
> captured dump survive.
Please try this change. What is happening is that you have a remaining
window that is smaller than the window scale. You are receiving zero
window updates that are received ok (becuase the socket buffer isn't
completely empty), and that advance rcv_nxt. However, tcp_output() is
not advancing rcv_adv because 'recwin' is calculated as zero. My
invariants had assumed that the ACK that gets forced out for a reply
to a zero window probe would move rcv_adv, but that isn't happening.
This patch will allow rcv_adv to advance when a zero window probe is
ACK'd. I'm not sure if this is the best way to fix this, but I think
it will fix it:
Index: tcp_output.c
===================================================================
--- tcp_output.c (revision 222565)
+++ tcp_output.c (working copy)
@@ -1331,7 +1331,7 @@ out:
* then remember the size of the advertised window.
* Any pending ACK has now been sent.
*/
- if (recwin > 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
+ if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
tp->rcv_adv = tp->rcv_nxt + recwin;
tp->last_ack_sent = tp->rcv_nxt;
tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
--
John Baldwin
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