Date: Sat, 5 May 2012 21:10:05 +0400 From: Gleb Smirnoff <glebius@FreeBSD.org> To: src-committers@FreeBSD.org, svn-src-all@FreeBSD.org, svn-src-stable@FreeBSD.org, svn-src-stable-8@FreeBSD.org Subject: Re: svn commit: r235053 - stable/8/sys/netinet Message-ID: <20120505171005.GP18777@FreeBSD.org> In-Reply-To: <201205051005.q45A5DTD050083@svn.freebsd.org> References: <201205051005.q45A5DTD050083@svn.freebsd.org>
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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> T> Log: 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> 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> 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> T> Reported by: az T> Reported by: Andrey Zonov <andrey zonov.org> T> Reviewed by: andre (previous version of patch) T> 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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