Hello, David, Jan. В Сбт, 13/10/2007 в 19:59 +0100, David пишет: > Try > > echo 0 > /proc/sys/net/ipv4/tcp_window_scaling > > I bet you have broken router(s) between your machine and the problem > site(s). Thank you for your help, but it occurs that the problem comes from IMQ patch. I've reported that on imqlinux mailing list, but seems that it's closed for those who do not have yahoo ID so I copy my report there and answer here. ===========my investigation of the problem================= This bug was reported in our bugzilla ( bugs.gentoo.org/195731 ) but as I found that IMQ is the root of problems I wanted to share my experience here. Starting with 2.6.21 (or may be 2.6.20 as I have not tried it) kernel I have problem that most tcp based services freeze at some point of operation. I've noticed this first on ssh but then found out that at lease one other service became similarly. The problem sites somewhere in the kernel as I've compiled 2.6.19, 2.6.21, and 2.6.22 with the similar .config options (of course not exact, as some options does not exist in some kernels, but seems that enabled options are all the same) but I have this problem only with the 21 and 22. I've tried to debug the problem a bit, but not a lot as that is production box working as linux based firewall/router. First I took tcpdump. Although ssh connection to the router is not always possible as it often hangs before I get into router, after some attempts ssh connection was established. On client computer I've started tcpdump and worked a bit until hang. tcpdump output showed me that when I press any keys the packets are sent to the server and proper ack are received. Later I found that all commands I enter blindly are executed on router but I receive no reply packets with some data in them (pure ack). That's why nothing happens on the screen and it looks like hanging. Now I've got to the router started ssh connection from router to some other server. It hanged too. I attached strace and found that ssh receive keyboard pressings (read() calls in the output) and writes them further to the kernel (write() calls) but tcpdump on the router shows no packets. So packets enter kernel and lost somewhere inside. This problem was reproduced both on single core amd64 system and on x86 system with hyper threading. So I suspect everybody could reproduce this problem. Just start `yes` which produce a lot of output and then press Ctrl+C to interupt. It hanged here somewhere at this moment. Suggestion "echo 0 > /proc/sys/net/ipv4/tcp_window_scaling" does not helped here. The end of the story is that if I localized that the problem sites in this http://www.linuximq.net/patchs/linux-2.6.21-img2.diff IMQ patch. If I install clean gentoo sources then connection does not freeze and with this patch I have problems. BTW. This patch http://www.actusa.net/~linuximq/linux-2.6.23-imq.diff does not have this problem here too. Thank you for your attention. I think may be it's good idea to mark that patch as questionable on site? =========================================================== ======== vlad031 answer on linuximq mailing list=========== Re: regression(?): starting with 2.6.21 sending packets became broken We allready know that ... almost everybody does ... that's why we have uploaded the good patches here: http://www.actusa.net/~linuximq/ Andree isn't seem to take care of this project anymore... Please note that 2.6.23 kernel has a lot of bugs and we don't recommend using it yet as we had some imq problems related too (however, it doesnt seem to be from imq patch) Cheers! =========================================================== -- Peter.
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