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,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 7040CC47089 for ; Wed, 26 May 2021 06:42:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4FA2A613D2 for ; Wed, 26 May 2021 06:42:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232678AbhEZGny (ORCPT ); Wed, 26 May 2021 02:43:54 -0400 Received: from www62.your-server.de ([213.133.104.62]:44712 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232336AbhEZGnw (ORCPT ); Wed, 26 May 2021 02:43:52 -0400 Received: from sslproxy05.your-server.de ([78.46.172.2]) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1llnF7-00074V-5W; Wed, 26 May 2021 08:42:13 +0200 Received: from [85.7.101.30] (helo=linux.home) by sslproxy05.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1llnF6-000Rf8-SY; Wed, 26 May 2021 08:42:12 +0200 Subject: Re: [PATCH v7 bpf-next 00/11] Socket migration for SO_REUSEPORT. To: Kuniyuki Iwashima , "David S . Miller" , Jakub Kicinski , Eric Dumazet , Alexei Starovoitov , Andrii Nakryiko , Martin KaFai Lau Cc: Benjamin Herrenschmidt , Kuniyuki Iwashima , bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, ncardwell@google.com, ycheng@google.com References: <20210521182104.18273-1-kuniyu@amazon.co.jp> From: Daniel Borkmann Message-ID: Date: Wed, 26 May 2021 08:42:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20210521182104.18273-1-kuniyu@amazon.co.jp> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.103.2/26181/Tue May 25 13:17:38 2021) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/21/21 8:20 PM, Kuniyuki Iwashima wrote: > The SO_REUSEPORT option allows sockets to listen on the same port and to > accept connections evenly. However, there is a defect in the current > implementation [1]. When a SYN packet is received, the connection is tied > to a listening socket. Accordingly, when the listener is closed, in-flight > requests during the three-way handshake and child sockets in the accept > queue are dropped even if other listeners on the same port could accept > such connections. > > This situation can happen when various server management tools restart > server (such as nginx) processes. For instance, when we change nginx > configurations and restart it, it spins up new workers that respect the new > configuration and closes all listeners on the old workers, resulting in the > in-flight ACK of 3WHS is responded by RST. > > To avoid such a situation, users have to know deeply how the kernel handles > SYN packets and implement connection draining by eBPF [2]: > > 1. Stop routing SYN packets to the listener by eBPF. > 2. Wait for all timers to expire to complete requests > 3. Accept connections until EAGAIN, then close the listener. > > or > > 1. Start counting SYN packets and accept syscalls using the eBPF map. > 2. Stop routing SYN packets. > 3. Accept connections up to the count, then close the listener. > > In either way, we cannot close a listener immediately. However, ideally, > the application need not drain the not yet accepted sockets because 3WHS > and tying a connection to a listener are just the kernel behaviour. The > root cause is within the kernel, so the issue should be addressed in kernel > space and should not be visible to user space. This patchset fixes it so > that users need not take care of kernel implementation and connection > draining. With this patchset, the kernel redistributes requests and > connections from a listener to the others in the same reuseport group > at/after close or shutdown syscalls. > > Although some software does connection draining, there are still merits in > migration. For some security reasons, such as replacing TLS certificates, > we may want to apply new settings as soon as possible and/or we may not be > able to wait for connection draining. The sockets in the accept queue have > not started application sessions yet. So, if we do not drain such sockets, > they can be handled by the newer listeners and could have a longer > lifetime. It is difficult to drain all connections in every case, but we > can decrease such aborted connections by migration. In that sense, > migration is always better than draining. > > Moreover, auto-migration simplifies user space logic and also works well in > a case where we cannot modify and build a server program to implement the > workaround. > > Note that the source and destination listeners MUST have the same settings > at the socket API level; otherwise, applications may face inconsistency and > cause errors. In such a case, we have to use the eBPF program to select a > specific listener or to cancel migration. > > Special thanks to Martin KaFai Lau for bouncing ideas and exchanging code > snippets along the way. > > > Link: > [1] The SO_REUSEPORT socket option > https://lwn.net/Articles/542629/ > > [2] Re: [PATCH 1/1] net: Add SO_REUSEPORT_LISTEN_OFF socket option as drain mode > https://lore.kernel.org/netdev/1458828813.10868.65.camel@edumazet-glaptop3.roam.corp.google.com/ This series needs review/ACKs from TCP maintainers. Eric/Neal/Yuchung please take a look again. Thanks, Daniel