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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 4B2AFCA9EAF for ; Thu, 24 Oct 2019 15:20:42 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1668B20679 for ; Thu, 24 Oct 2019 15:20:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OxSWAlCH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1668B20679 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45276 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iNeum-0002b2-5y for qemu-devel@archiver.kernel.org; Thu, 24 Oct 2019 11:20:40 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:46521) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iNesK-0008MY-W0 for qemu-devel@nongnu.org; Thu, 24 Oct 2019 11:18:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iNesJ-0002If-Iw for qemu-devel@nongnu.org; Thu, 24 Oct 2019 11:18:08 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:20334 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iNesJ-0002AD-CH for qemu-devel@nongnu.org; Thu, 24 Oct 2019 11:18:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1571930200; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Aj2fw3kqMhaYujJmwNQfIp4SzI0JZ/mxRbbJUYOMzuc=; b=OxSWAlCHRDVqDSPGkWDtiy06GAr3siYeFotEaxc2N/wwOsyYEWNNHyg2H4N5qJTVyypOWN MKEE6s0lm7y0gDhURGVPpMnu9Xfk+lCgqailoxazAd6EpRf870RH2rZEpcZrLjRIpeC5BF VmuUj61XLT45WTzWsd5fLgLrO02TETM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-94-2WHtewz8NxSOqUEFzulKwQ-1; Thu, 24 Oct 2019 11:05:43 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 62EF985EE90; Thu, 24 Oct 2019 14:34:56 +0000 (UTC) Received: from redhat.com (unknown [10.42.16.231]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 61FB13DB4; Thu, 24 Oct 2019 14:34:52 +0000 (UTC) Date: Thu, 24 Oct 2019 15:34:50 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: cenjiahui Subject: Re: [PATCH 3/3] migration/multifd: fix potential wrong acception order of IOChannel Message-ID: <20191024143450.GF8381@redhat.com> References: <20191023033214.31592-1-cenjiahui@huawei.com> <20191023033214.31592-3-cenjiahui@huawei.com> <20191024095227.GC3700@redhat.com> <1356aa1a-346d-29a7-8064-ac1e572b6512@huawei.com> MIME-Version: 1.0 In-Reply-To: <1356aa1a-346d-29a7-8064-ac1e572b6512@huawei.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: 2WHtewz8NxSOqUEFzulKwQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: quintela@redhat.com, qemu-devel@nongnu.org, zhouyibo3@huawei.com, dgilbert@redhat.com, peterx@redhat.com, fangying1@huawei.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Oct 24, 2019 at 09:53:24PM +0800, cenjiahui wrote: > On 2019/10/24 17:52, Daniel P. Berrang=C3=A9 wrote: > > On Wed, Oct 23, 2019 at 11:32:14AM +0800, cenjiahui wrote: > >> From: Jiahui Cen > >> > >> Multifd assumes the migration thread IOChannel is always established b= efore > >> the multifd IOChannels, but this assumption will be broken in many sit= uations > >> like network packet loss. > >> > >> For example: > >> Step1: Source (migration thread IOChannel) --SYN--> Destination > >> Step2: Source (migration thread IOChannel) <--SYNACK Destination > >> Step3: Source (migration thread IOChannel, lost) --ACK-->X Destinatio= n > >> Step4: Source (multifd IOChannel) --SYN--> Destination > >> Step5: Source (multifd IOChannel) <--SYNACK Destination > >> Step6: Source (multifd IOChannel, ESTABLISHED) --ACK--> Destination > >> Step7: Destination accepts multifd IOChannel > >> Step8: Source (migration thread IOChannel, ESTABLISHED) -ACK,DATA-> D= estination > >> Step9: Destination accepts migration thread IOChannel > >> > >> The above situation can be reproduced by creating a weak network envir= onment, > >> such as "tc qdisc add dev eth0 root netem loss 50%". The wrong accepti= on order > >> will cause magic check failure and thus lead to migration failure. > >> > >> This patch fixes this issue by sending a migration IOChannel initial p= acket with > >> a unique id when using multifd migration. Since the multifd IOChannels= will also > >> send initial packets, the destination can judge whether the processing= IOChannel > >> belongs to multifd by checking the id in the initial packet. This mech= anism can > >> ensure that different IOChannels will go to correct branches in our te= st. > >=20 > > Isn't this going to break back compatibility when new QEMU talks to old > > QEMU with multifd enabled ? New QEMU will be sending a packet that old > > QEMU isn't expecting IIUC. >=20 > Yes, it actually breaks back compatibility. But since the old QEMU has bu= g with > multifd, it may be not suitable to use multifd to migrate from new QEMU t= o old > QEMU in my opinion. We declared multifd supported from v4.0.0 onwards, so changing the wire protocol in non-backwards compatibles ways is not acceptable IMHO. Ideally we'd change QEMU so that the src QEMU serializes the connections, such that the migration thread I/O channel is established before we attempt to establish the multifd channels. If changing the wire protocol is unavoidable, then we'd need to invent a new migration capability for the mgmt apps to detect & opt-in to when both sides support it. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberrange= :| |: https://libvirt.org -o- https://fstop138.berrange.com= :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange= :|