From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A360C2D0A3 for ; Mon, 9 Nov 2020 16:26:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 03E1E206CB for ; Mon, 9 Nov 2020 16:26:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730185AbgKIQ0q (ORCPT ); Mon, 9 Nov 2020 11:26:46 -0500 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:45871 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729791AbgKIQ0p (ORCPT ); Mon, 9 Nov 2020 11:26:45 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04400;MF=wenan.mao@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0UEmInaP_1604939200; Received: from B-44NBMD6M-0121.local(mailfrom:wenan.mao@linux.alibaba.com fp:SMTPD_---0UEmInaP_1604939200) by smtp.aliyun-inc.com(127.0.0.1); Tue, 10 Nov 2020 00:26:40 +0800 Subject: Re: [PATCH net v2] net: Update window_clamp if SOCK_RCVBUF is set To: Eric Dumazet Cc: David Miller , Alexey Kuznetsov , Hideaki YOSHIFUJI , Jakub Kicinski , netdev , LKML , kernel-janitors@vger.kernel.org References: <1604913614-19432-1-git-send-email-wenan.mao@linux.alibaba.com> <1604914417-24578-1-git-send-email-wenan.mao@linux.alibaba.com> <3b92167c-201c-e85d-822d-06f0c9ac508c@linux.alibaba.com> From: Mao Wenan Message-ID: <302ad089-9e82-1856-0652-b92251c14e37@linux.alibaba.com> Date: Tue, 10 Nov 2020 00:26:40 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.3.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2020/11/9 下午10:01, Eric Dumazet 写道: > On Mon, Nov 9, 2020 at 12:41 PM Eric Dumazet wrote: >> >> Packetdrill test would be : >> >> // Force syncookies >> `sysctl -q net.ipv4.tcp_syncookies=2` >> >> 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 >> +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 >> +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [2048], 4) = 0 >> +0 bind(3, ..., ...) = 0 >> +0 listen(3, 1) = 0 >> >> +0 < S 0:0(0) win 32792 >> +0 > S. 0:0(0) ack 1 >> +.1 < . 1:1(0) ack 1 win 1024 >> +0 accept(3, ..., ...) = 4 >> +0 %{ assert tcpi_snd_wscale == 0, tcpi_snd_wscale }% >> > > Also, please add to your next submission an appropriate Fixes: tag : > > Fixes: e88c64f0a425 ("tcp: allow effective reduction of TCP's > rcv-buffer via setsockopt") OK, thanks, I can reproduce wscale=0 with your packetdrill, and I will send v3 with the fixes tag. > >> On Mon, Nov 9, 2020 at 12:02 PM Eric Dumazet wrote: >>> >>> On Mon, Nov 9, 2020 at 11:12 AM Mao Wenan wrote: >>>> >>>> >>>> >>>> 在 2020/11/9 下午5:56, Eric Dumazet 写道: >>>>> On Mon, Nov 9, 2020 at 10:33 AM Mao Wenan wrote: >>>>>> >>>>>> When net.ipv4.tcp_syncookies=1 and syn flood is happened, >>>>>> cookie_v4_check or cookie_v6_check tries to redo what >>>>>> tcp_v4_send_synack or tcp_v6_send_synack did, >>>>>> rsk_window_clamp will be changed if SOCK_RCVBUF is set, >>>>>> which will make rcv_wscale is different, the client >>>>>> still operates with initial window scale and can overshot >>>>>> granted window, the client use the initial scale but local >>>>>> server use new scale to advertise window value, and session >>>>>> work abnormally. >>>>> >>>>> What is not working exactly ? >>>>> >>>>> Sending a 'big wscale' should not really matter, unless perhaps there >>>>> is a buggy stack at the remote end ? >>>> 1)in tcp_v4_send_synack, if SO_RCVBUF is set and >>>> tcp_full_space(sk)=65535, pass req->rsk_window_clamp=65535 to >>>> tcp_select_initial_window, rcv_wscale will be zero, and send to client, >>>> the client consider wscale is 0; >>>> 2)when ack is back from client, if there is no this patch, >>>> req->rsk_window_clamp is 0, and pass to tcp_select_initial_window, >>>> wscale will be 7, this new rcv_wscale is no way to advertise to client. >>>> 3)if server send rcv_wind to client with window=63, it consider the real >>>> window is 63*2^7=8064, but client consider the server window is only >>>> 63*2^0=63, it can't send big packet to server, and the send-q of client >>>> is full. >>>> >>> >>> I see, please change your patches so that tcp_full_space() is used _once_ >>> >>> listener sk_rcvbuf can change under us. >>> >>> I really have no idea how window can be set to 63, so please send us >>> the packetdrill test once you have it.