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_2 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 B1997C33CB6 for ; Thu, 16 Jan 2020 08:50:17 +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 8871A2073A for ; Thu, 16 Jan 2020 08:50:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8871A2073A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kaod.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:38456 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1is0r2-0002fa-PJ for qemu-devel@archiver.kernel.org; Thu, 16 Jan 2020 03:50:16 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:60592) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1is0pz-0001JI-Jr for qemu-devel@nongnu.org; Thu, 16 Jan 2020 03:49:15 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1is0pv-0004el-QR for qemu-devel@nongnu.org; Thu, 16 Jan 2020 03:49:11 -0500 Received: from 9.mo179.mail-out.ovh.net ([46.105.76.148]:51089) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1is0pu-0004d5-Gv for qemu-devel@nongnu.org; Thu, 16 Jan 2020 03:49:07 -0500 Received: from player746.ha.ovh.net (unknown [10.108.16.46]) by mo179.mail-out.ovh.net (Postfix) with ESMTP id D6BD315650C for ; Thu, 16 Jan 2020 09:49:02 +0100 (CET) Received: from kaod.org (lns-bzn-46-82-253-208-248.adsl.proxad.net [82.253.208.248]) (Authenticated sender: groug@kaod.org) by player746.ha.ovh.net (Postfix) with ESMTPSA id 57B95E5AD7EF; Thu, 16 Jan 2020 08:48:53 +0000 (UTC) Date: Thu, 16 Jan 2020 09:48:48 +0100 From: Greg Kurz To: Laurent Vivier Subject: Re: [PATCH] spapr: Migrate CAS reboot flag Message-ID: <20200116094848.555c170d@bahia.lan> In-Reply-To: References: <157911051688.345768.16136592081655557565.stgit@bahia.lan> X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Ovh-Tracer-Id: 2557481640314116390 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedugedrtdeggdduudelucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuqfggjfdpvefjgfevmfevgfenuceurghilhhouhhtmecuhedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhepfffhvffukfgjfhfogggtgfesthhqredtredtjeenucfhrhhomhepifhrvghgucfmuhhriicuoehgrhhouhhgsehkrghougdrohhrgheqnecukfhppedtrddtrddtrddtpdekvddrvdehfedrvddtkedrvdegkeenucfrrghrrghmpehmohguvgepshhmthhpqdhouhhtpdhhvghlohepphhlrgihvghrjeegiedrhhgrrdhovhhhrdhnvghtpdhinhgvtheptddrtddrtddrtddpmhgrihhlfhhrohhmpehgrhhouhhgsehkrghougdrohhrghdprhgtphhtthhopehqvghmuhdquggvvhgvlhesnhhonhhgnhhurdhorhhgnecuvehluhhsthgvrhfuihiivgeptd X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 46.105.76.148 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: Lukas Doktor , Juan Quintela , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , qemu-ppc@nongnu.org, =?UTF-8?B?Q8OpZHJpYw==?= Le Goater , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 15 Jan 2020 19:10:37 +0100 Laurent Vivier wrote: > Hi, >=20 > On 15/01/2020 18:48, Greg Kurz wrote: > > Migration can potentially race with CAS reboot. If the migration thread > > completes migration after CAS has set spapr->cas_reboot but before the > > mainloop could pick up the reset request and reset the machine, the > > guest is migrated unrebooted and the destination doesn't reboot it > > either because it isn't aware a CAS reboot was needed (eg, because a > > device was added before CAS). This likely result in a broken or hung > > guest. > >=20 > > Even if it is small, the window between CAS and CAS reboot is enough to > > re-qualify spapr->cas_reboot as state that we should migrate. Add a new > > subsection for that and always send it when a CAS reboot is pending. > > This may cause migration to older QEMUs to fail but it is still better > > than end up with a broken guest. > >=20 > > The destination cannot honour the CAS reboot request from a post load > > handler because this must be done after the guest is fully restored. > > It is thus done from a VM change state handler. > >=20 > > Reported-by: Luk=C3=A1=C5=A1 Doktor > > Signed-off-by: Greg Kurz > > --- > >=20 >=20 > I'm wondering if the problem can be related with the fact that > main_loop_should_exit() could release qemu_global_mutex in > pause_all_vcpus() in the reset case? >=20 > 1602 static bool main_loop_should_exit(void) > 1603 { > ... > 1633 request =3D qemu_reset_requested(); > 1634 if (request) { > 1635 pause_all_vcpus(); > 1636 qemu_system_reset(request); > 1637 resume_all_vcpus(); > 1638 if (!runstate_check(RUN_STATE_RUNNING) && > 1639 !runstate_check(RUN_STATE_INMIGRATE)) { > 1640 runstate_set(RUN_STATE_PRELAUNCH); > 1641 } > 1642 } > ... >=20 > I already sent a patch for this kind of problem (in current Juan pull > request): >=20 > "runstate: ignore finishmigrate -> prelaunch transition" >=20 IIUC your patch avoids an invalid 'prelaunch' -> 'postmigrate' runstate transition that can happen if the migration thread sets the runstate to 'finishmigrate' when pause_all_vcpus() releases the main loop mutex. ie. symptom of the problem is QEMU aborting, correct ? The issue I'm trying to fix is a guest breakage caused by a discrepancy between QEMU and the guest after migration has succeeded. > but I don't know if it could fix this one. >=20 I don't think so and your patch kinda illustrates it. If the runstate is 'finishmigrate' when returning from pause_all_vcpus(), this means that state was sent to the destination before we could actually reset the machine. > Thanks, > Laurent >=20