svn commit: r235053 - stable/8/sys/netinet
glebius at FreeBSD.org
Sat May 5 17:10:18 UTC 2012
On Sat, May 05, 2012 at 10:05:13AM +0000, Gleb Smirnoff wrote:
T> Author: glebius
T> Date: Sat May 5 10:05:13 2012
T> New Revision: 235053
T> URL: http://svn.freebsd.org/changeset/base/235053
T> Merge 234342 from head:
T> When we receive an ICMP unreach need fragmentation datagram, we take
T> proposed MTU value from it and update the TCP host cache. Then
T> tcp_mss_update() is called on the corresponding tcpcb. It finds the
T> just allocated entry in the TCP host cache and updates MSS on the
T> tcpcb. And then we do a fast retransmit of what we have in the tcp
T> send buffer.
T> This sequence gets broken if the TCP host cache is exausted. In this
T> case allocation fails, and later called tcp_mss_update() finds nothing
T> in cache. The fast retransmit is done with not reduced MSS and is
T> immidiately replied by remote host with new ICMP datagrams and the
T> cycle repeats. This ping-pong can go up to wirespeed.
T> To fix this:
T> - tcp_mss_update() gets new parameter - mtuoffer, that is like
T> offer, but needs to have min_protoh subtracted.
T> - tcp_mtudisc() as notification method renamed to tcp_mtudisc_notify().
T> - tcp_mtudisc() now accepts not a useless error argument, but proposed
T> MTU value, that is passed to tcp_mss_update() as mtuoffer.
T> Reported by: az
T> Reported by: Andrey Zonov <andrey zonov.org>
T> Reviewed by: andre (previous version of patch)
T> Tested by: Andrey Zonov <andrey zonov.org>
Sorry, should have been: tested by az.
Andrej Zverev did extensive testing on stable/8.
Totus tuus, Glebius.
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