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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 88D37C47404 for ; Wed, 9 Oct 2019 16:40:20 +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 5CAD4206BB for ; Wed, 9 Oct 2019 16:40:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5CAD4206BB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:52420 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIF0c-0003lO-PR for qemu-devel@archiver.kernel.org; Wed, 09 Oct 2019 12:40:18 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59967) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iI58Z-0001TU-0e for qemu-devel@nongnu.org; Wed, 09 Oct 2019 02:07:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iI58X-0005tF-OF for qemu-devel@nongnu.org; Wed, 09 Oct 2019 02:07:50 -0400 Received: from mga18.intel.com ([134.134.136.126]:13581) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iI58X-0005rJ-Gj for qemu-devel@nongnu.org; Wed, 09 Oct 2019 02:07:49 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 08 Oct 2019 23:07:47 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.67,273,1566889200"; d="scan'208";a="205649977" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga002.jf.intel.com with ESMTP; 08 Oct 2019 23:07:45 -0700 Date: Wed, 9 Oct 2019 14:07:28 +0800 From: Wei Yang To: Peter Xu Subject: Re: [PATCH 3/3] migration/postcopy: handle POSTCOPY_INCOMING_RUNNING corner case properly Message-ID: <20191009060728.GA14892@richard> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191009053633.GA1039@xz-x1> User-Agent: Mutt/1.9.4 (2018-02-28) X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 134.134.136.126 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: Wei Yang Cc: qemu-devel@nongnu.org, quintela@redhat.com, Wei Yang , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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) > return -1; > postcopy_state_set(RUNNING); > Looks good to me. Dave, Do you feel good with it? >Thanks, > >-- >Peter Xu -- Wei Yang Help you, Help me