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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 00951C47404 for ; Wed, 9 Oct 2019 17:55:39 +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 C8B0E206BB for ; Wed, 9 Oct 2019 17:55:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C8B0E206BB 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]:53380 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIGBV-0005p0-7C for qemu-devel@archiver.kernel.org; Wed, 09 Oct 2019 13:55:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49828) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iI7xi-0002SZ-Qq for qemu-devel@nongnu.org; Wed, 09 Oct 2019 05:08:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iI7xh-0003as-Ks for qemu-devel@nongnu.org; Wed, 09 Oct 2019 05:08:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36544) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iI7xh-0003aa-Cj for qemu-devel@nongnu.org; Wed, 09 Oct 2019 05:08:49 -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 mx1.redhat.com (Postfix) with ESMTPS id 76BCC18CB8EC; Wed, 9 Oct 2019 09:08:48 +0000 (UTC) Received: from work-vm (ovpn-117-215.ams2.redhat.com [10.36.117.215]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 23055F6C2; Wed, 9 Oct 2019 09:08:44 +0000 (UTC) Date: Wed, 9 Oct 2019 10:08:42 +0100 From: "Dr. David Alan Gilbert" To: Wei Yang Subject: Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly Message-ID: <20191009090842.GD2893@work-vm> References: <20191001100122.17730-1-richardw.yang@linux.intel.com> <20191001100122.17730-4-richardw.yang@linux.intel.com> <20191008164046.GF3441@work-vm> <20191009010204.GC26203@richard> <20191009041225.GF10750@xz-x1> <20191009050756.GA9616@richard> <20191009053633.GA1039@xz-x1> <20191009060728.GA14892@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191009060728.GA14892@richard> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.63]); Wed, 09 Oct 2019 09:08:48 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 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: , Cc: qemu-devel@nongnu.org, Peter Xu , quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Wei Yang (richardw.yang@linux.intel.com) wrote: > On Wed, Oct 09, 2019 at 01:36:34PM +0800, Peter Xu wrote: > >On Wed, Oct 09, 2019 at 01:07:56PM +0800, Wei Yang wrote: > >> On Wed, Oct 09, 2019 at 12:12:25PM +0800, Peter Xu wrote: > >> >On Wed, Oct 09, 2019 at 09:02:04AM +0800, Wei Yang wrote: > >> >> On Tue, Oct 08, 2019 at 05:40:46PM +0100, Dr. David Alan Gilbert wrote: > >> >> >* Wei Yang (richardw.yang@linux.intel.com) wrote: > >> >> >> Currently, we set PostcopyState blindly to RUNNING, even we found the > >> >> >> previous state is not LISTENING. This will lead to a corner case. > >> >> >> > >> >> >> First let's look at the code flow: > >> >> >> > >> >> >> qemu_loadvm_state_main() > >> >> >> ret = loadvm_process_command() > >> >> >> loadvm_postcopy_handle_run() > >> >> >> return -1; > >> >> >> if (ret < 0) { > >> >> >> if (postcopy_state_get() == POSTCOPY_INCOMING_RUNNING) > >> >> >> ... > >> >> >> } > >> >> >> > >> >> >> From above snippet, the corner case is loadvm_postcopy_handle_run() > >> >> >> always sets state to RUNNING. And then it checks the previous state. If > >> >> >> the previous state is not LISTENING, it will return -1. But at this > >> >> >> moment, PostcopyState is already been set to RUNNING. > >> >> >> > >> >> >> Then ret is checked in qemu_loadvm_state_main(), when it is -1 > >> >> >> PostcopyState is checked. Current logic would pause postcopy and retry > >> >> >> if PostcopyState is RUNNING. This is not what we expect, because > >> >> >> postcopy is not active yet. > >> >> >> > >> >> >> This patch makes sure state is set to RUNNING only previous state is > >> >> >> LISTENING by introducing an old_state parameter in postcopy_state_set(). > >> >> >> New state only would be set when current state equals to old_state. > >> >> >> > >> >> >> Signed-off-by: Wei Yang > >> >> > > >> >> >OK, it's a shame to use a pointer there, but it works. > >> >> > >> >> You mean second parameter of postcopy_state_set()? > >> >> > >> >> I don't have a better idea. Or we introduce a new state > >> >> POSTCOPY_INCOMING_NOCHECK. Do you feel better with this? > >> > > >> >Maybe simply fix loadvm_postcopy_handle_run() to set the state after > >> >the POSTCOPY_INCOMING_LISTENING check? > >> > > >> > >> Set state back to ps if ps is not POSTCOPY_INCOMING_LISTENING? > >> > >> Sounds like another option. > > > >Even simpler? > > > > ps = postcopy_state_get(); > > if (ps != INCOMING) ^^ LISTENING > > return -1; > > postcopy_state_set(RUNNING); > > > > Looks good to me. > > Dave, > > Do you feel good with it? Yes, I think so; it's simpler. Dave > >Thanks, > > > >-- > >Peter Xu > > -- > Wei Yang > Help you, Help me -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK