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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 596CCC2D0DB for ; Fri, 31 Jan 2020 14:00:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3739020705 for ; Fri, 31 Jan 2020 14:00:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728770AbgAaOAc convert rfc822-to-8bit (ORCPT ); Fri, 31 Jan 2020 09:00:32 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:45944 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728752AbgAaOAb (ORCPT ); Fri, 31 Jan 2020 09:00:31 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-242-JHDjgXV-PJqc_fZ2W4bcWg-1; Fri, 31 Jan 2020 14:00:28 +0000 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 31 Jan 2020 14:00:27 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 31 Jan 2020 14:00:27 +0000 From: David Laight To: "'sjpark@amazon.com'" , "edumazet@google.com" , "davem@davemloft.net" CC: "shuah@kernel.org" , "netdev@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "sj38.park@gmail.com" , "aams@amazon.com" , SeongJae Park Subject: RE: [PATCH 0/3] Fix reconnection latency caused by FIN/ACK handling race Thread-Topic: [PATCH 0/3] Fix reconnection latency caused by FIN/ACK handling race Thread-Index: AQHV2DFvc3pd6ARlHUK3D8H5esqW/agEyn3w Date: Fri, 31 Jan 2020 14:00:27 +0000 Message-ID: References: <20200131122421.23286-1-sjpark@amazon.com> In-Reply-To: <20200131122421.23286-1-sjpark@amazon.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: JHDjgXV-PJqc_fZ2W4bcWg-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org From: sjpark@amazon.com > Sent: 31 January 2020 12:24 ... > The acks in lines 6 and 8 are the acks. If the line 8 packet is > processed before the line 6 packet, it will be just ignored as it is not > a expected packet, and the later process of the line 6 packet will > change the status of Process A to FIN_WAIT_2, but as it has already > handled line 8 packet, it will not go to TIME_WAIT and thus will not > send the line 10 packet to Process B. Thus, Process B will left in > CLOSE_WAIT status, as below. > > 00 (Process A) (Process B) > 01 ESTABLISHED ESTABLISHED > 02 close() > 03 FIN_WAIT_1 > 04 ---FIN--> > 05 CLOSE_WAIT > 06 (<--ACK---) > 07 (<--FIN/ACK---) > 08 (fired in right order) > 09 <--FIN/ACK--- > 10 <--ACK--- > 11 (processed in reverse order) > 12 FIN_WAIT_2 Why doesn't A treat the FIN/ACK (09) as valid (as if the ACK had got lost) and then ignore the ACK (10) because it refers to a closed socket? I presume that B sends two ACKs (06 and 07) because it can sit in an intermediate state and the first ACK stops the FIN being resent? I've implemented lots of protocols in my time, but not TCP. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)