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=-7.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,PDS_BTC_ID, 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 A94BEC43603 for ; Fri, 6 Dec 2019 19:53:44 +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 728662464E for ; Fri, 6 Dec 2019 19:53:44 +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="bdp0FY3C" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 728662464E 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]:44838 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1idJfb-0002XH-L2 for qemu-devel@archiver.kernel.org; Fri, 06 Dec 2019 14:53:43 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:39528) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1idJea-0001yB-8f for qemu-devel@nongnu.org; Fri, 06 Dec 2019 14:52:41 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1idJeY-00066r-Vj for qemu-devel@nongnu.org; Fri, 06 Dec 2019 14:52:40 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:46540 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 1idJeY-00063w-PN for qemu-devel@nongnu.org; Fri, 06 Dec 2019 14:52:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1575661956; h=from:from: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=zFeey+Cm4zctfKPSXMOHndeziaIISHty2K196N9AGjA=; b=bdp0FY3CcFKyi0N2Zv/TPR/ju6cIusSqCfYkXb3KmX5PA+FIxsrFM3ub+B34wg2NaoFxIu 5O24Qas3G0HrAJRMLdUrwAwTD8r+7+HXpHu+4xxYNSHHOVuKWyaGiBxs2k4pEwnHzXce84 XIvL9nbg6c4ypV/lpZ8KAkJ+3OopnNY= 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-371-E4KGJv_gMtK049AjUFhPMg-1; Fri, 06 Dec 2019 14:52:35 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2B9C2800D54 for ; Fri, 6 Dec 2019 19:52:34 +0000 (UTC) Received: from work-vm (ovpn-117-232.ams2.redhat.com [10.36.117.232]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F08FE60179; Fri, 6 Dec 2019 19:52:32 +0000 (UTC) Date: Fri, 6 Dec 2019 19:52:30 +0000 From: "Dr. David Alan Gilbert" To: Laurent Vivier Subject: Re: [PATCH] runstate: ignore finishmigrate -> prelaunch transition Message-ID: <20191206195230.GJ2878@work-vm> References: <20191129115132.285988-1-lvivier@redhat.com> MIME-Version: 1.0 In-Reply-To: <20191129115132.285988-1-lvivier@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-MC-Unique: E4KGJv_gMtK049AjUFhPMg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=us-ascii 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: 207.211.31.120 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: , Cc: Paolo Bonzini , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Laurent Vivier (lvivier@redhat.com) wrote: > Commit 1bd71dce4bf2 tries to prevent a finishmigrate -> prelaunch > transition by exiting at the beginning of the main_loop_should_exit() > function if the state is already finishmigrate. >=20 > As the finishmigrate state is set in the migration thread it can > happen concurrently to the function. The migration thread and the > function are normally protected by the iothread mutex and thus the > state should no evolve between the start of the function and its end. >=20 > Unfortunately during the function life the lock is released by > pause_all_vcpus() just before the point we need to be sure we are > not in finishmigrate state and if the migration thread is waiting > for the lock it will take the opportunity to change the state > to finishmigrate. Ewww. I hate those short wakeups for pause_all_vcpus; I'm sure there are loads more corners that break. Still, I _think_ this is an improvement, so: Reviewed-by: Dr. David Alan Gilbert > The only way to be sure we are not in the finishmigrate state when > we need is to check the state after the pause_all_vcpus() function. >=20 > Fixes: 1bd71dce4bf2 ("runstate: ignore exit request in finish migrate sta= te") > Signed-off-by: Laurent Vivier > --- > vl.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) >=20 > diff --git a/vl.c b/vl.c > index 6a65a64bfd64..bf0a6345d239 100644 > --- a/vl.c > +++ b/vl.c > @@ -1745,9 +1745,6 @@ static bool main_loop_should_exit(void) > RunState r; > ShutdownCause request; > =20 > - if (runstate_check(RUN_STATE_FINISH_MIGRATE)) { > - return false; > - } > if (preconfig_exit_requested) { > if (runstate_check(RUN_STATE_PRECONFIG)) { > runstate_set(RUN_STATE_PRELAUNCH); > @@ -1776,8 +1773,13 @@ static bool main_loop_should_exit(void) > pause_all_vcpus(); > qemu_system_reset(request); > resume_all_vcpus(); > + /* > + * runstate can change in pause_all_vcpus() > + * as iothread mutex is unlocked > + */ > if (!runstate_check(RUN_STATE_RUNNING) && > - !runstate_check(RUN_STATE_INMIGRATE)) { > + !runstate_check(RUN_STATE_INMIGRATE) && > + !runstate_check(RUN_STATE_FINISH_MIGRATE)) { > runstate_set(RUN_STATE_PRELAUNCH); > } > } > --=20 > 2.23.0 >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK