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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 5FC3EC47404 for ; Fri, 11 Oct 2019 10:13:06 +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 2F4672190F for ; Fri, 11 Oct 2019 10:13:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2F4672190F 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]:48082 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIruz-00087w-68 for qemu-devel@archiver.kernel.org; Fri, 11 Oct 2019 06:13:05 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33171) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIruD-0007i5-W8 for qemu-devel@nongnu.org; Fri, 11 Oct 2019 06:12:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iIruC-0003ch-LE for qemu-devel@nongnu.org; Fri, 11 Oct 2019 06:12:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38402) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iIruC-0003cS-FO for qemu-devel@nongnu.org; Fri, 11 Oct 2019 06:12:16 -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 6EAA710C0932; Fri, 11 Oct 2019 10:12:15 +0000 (UTC) Received: from work-vm (ovpn-117-210.ams2.redhat.com [10.36.117.210]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A0E4A196B2; Fri, 11 Oct 2019 10:12:11 +0000 (UTC) Date: Fri, 11 Oct 2019 11:12:09 +0100 From: "Dr. David Alan Gilbert" To: Wei Yang Subject: Re: [PATCH v2 2/2] migration/postcopy: check PostcopyState before setting to POSTCOPY_INCOMING_RUNNING Message-ID: <20191011101209.GM3354@work-vm> References: <20191010011316.31363-1-richardw.yang@linux.intel.com> <20191010011316.31363-3-richardw.yang@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191010011316.31363-3-richardw.yang@linux.intel.com> 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 [10.5.110.66]); Fri, 11 Oct 2019 10:12:15 +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, peterx@redhat.com, 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: > 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 checking the state first. > > Signed-off-by: Wei Yang > Suggested by: Peter Xu Reviewed-by: Dr. David Alan Gilbert > --- > migration/savevm.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/migration/savevm.c b/migration/savevm.c > index 78c2965ca4..b9f30a7090 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -1934,7 +1934,7 @@ static void loadvm_postcopy_handle_run_bh(void *opaque) > /* After all discards we can start running and asking for pages */ > static int loadvm_postcopy_handle_run(MigrationIncomingState *mis) > { > - PostcopyState ps = postcopy_state_set(POSTCOPY_INCOMING_RUNNING); > + PostcopyState ps = postcopy_state_get(); > > trace_loadvm_postcopy_handle_run(); > if (ps != POSTCOPY_INCOMING_LISTENING) { > @@ -1942,6 +1942,7 @@ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis) > return -1; > } > > + postcopy_state_set(POSTCOPY_INCOMING_RUNNING); > mis->bh = qemu_bh_new(loadvm_postcopy_handle_run_bh, mis); > qemu_bh_schedule(mis->bh); > > -- > 2.17.1 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK