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 5D597C33CB6 for ; Thu, 16 Jan 2020 18:30:54 +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 2CB7A20684 for ; Thu, 16 Jan 2020 18:30:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2CB7A20684 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]:46802 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1is9uv-0007Bq-1j for qemu-devel@archiver.kernel.org; Thu, 16 Jan 2020 13:30:53 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:37309) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1is9tP-0005yl-NQ for qemu-devel@nongnu.org; Thu, 16 Jan 2020 13:29:23 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1is9tL-0007yg-T5 for qemu-devel@nongnu.org; Thu, 16 Jan 2020 13:29:19 -0500 Received: from 2.mo3.mail-out.ovh.net ([46.105.75.36]:34382) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1is9tL-0007x6-M7 for qemu-devel@nongnu.org; Thu, 16 Jan 2020 13:29:15 -0500 Received: from player695.ha.ovh.net (unknown [10.108.16.72]) by mo3.mail-out.ovh.net (Postfix) with ESMTP id 548A123CCC2 for ; Thu, 16 Jan 2020 19:29:13 +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 player695.ha.ovh.net (Postfix) with ESMTPSA id 77B3BE31553E; Thu, 16 Jan 2020 18:29:03 +0000 (UTC) Date: Thu, 16 Jan 2020 19:29:02 +0100 From: Greg Kurz To: Laurent Vivier Subject: Re: [PATCH] spapr: Migrate CAS reboot flag Message-ID: <20200116192902.63674769@bahia.lan> In-Reply-To: <20200116131435.3985e86e@bahia.lan> References: <157911051688.345768.16136592081655557565.stgit@bahia.lan> <20200116094848.555c170d@bahia.lan> <2dda458a-dfa1-ab23-4a97-d27d9266226b@redhat.com> <20200116131435.3985e86e@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: 12355907053416519974 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedugedrtdehgdduudduucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuqfggjfdpvefjgfevmfevgfenuceurghilhhouhhtmecuhedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhepfffhvffukfgjfhfogggtgfesthhqfedtredtjeenucfhrhhomhepifhrvghgucfmuhhriicuoehgrhhouhhgsehkrghougdrohhrgheqnecukfhppedtrddtrddtrddtpdekvddrvdehfedrvddtkedrvdegkeenucfrrghrrghmpehmohguvgepshhmthhpqdhouhhtpdhhvghlohepphhlrgihvghrieelhedrhhgrrdhovhhhrdhnvghtpdhinhgvtheptddrtddrtddrtddpmhgrihhlfhhrohhmpehgrhhouhhgsehkrghougdrohhrghdprhgtphhtthhopehqvghmuhdquggvvhgvlhesnhhonhhgnhhurdhorhhgnecuvehluhhsthgvrhfuihiivgeptd X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 46.105.75.36 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 Thu, 16 Jan 2020 13:14:35 +0100 Greg Kurz wrote: > On Thu, 16 Jan 2020 11:37:24 +0100 > Laurent Vivier wrote: >=20 > > On 16/01/2020 09:48, Greg Kurz wrote: > > > On Wed, 15 Jan 2020 19:10:37 +0100 > > > Laurent Vivier wrote: > > >=20 > > >> Hi, > > >> > > >> On 15/01/2020 18:48, Greg Kurz wrote: > > >>> Migration can potentially race with CAS reboot. If the migration th= read > > >>> 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. > > >>> > > >>> Even if it is small, the window between CAS and CAS reboot is enoug= h 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 bet= ter > > >>> than end up with a broken guest. > > >>> > > >>> The destination cannot honour the CAS reboot request from a post lo= ad > > >>> handler because this must be done after the guest is fully restored. > > >>> It is thus done from a VM change state handler. > > >>> > > >>> Reported-by: Luk=C3=A1=C5=A1 Doktor > > >>> Signed-off-by: Greg Kurz > > >>> --- > > >>> > > >> > > >> 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? > > >> > > >> 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 } > > >> ... > > >> > > >> I already sent a patch for this kind of problem (in current Juan pull > > >> request): > > >> > > >> "runstate: ignore finishmigrate -> prelaunch transition" > > >> > > >=20 > > > IIUC your patch avoids an invalid 'prelaunch' -> 'postmigrate' runsta= te > > > transition that can happen if the migration thread sets the runstate = to > > > 'finishmigrate' when pause_all_vcpus() releases the main loop mutex. > > >=20 > > > 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. > > >=20 > > >> 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. > >=20 > > Yes, you're right. > >=20 > > But the question behind my comment was: is it expected to have a pending > > reset while we are migrating? > >=20 >=20 > Nothing prevents qemu_system_reset_request() to be called when migration > is active.=20 >=20 > > Perhaps H_CAS can return H_BUSY and wait the end of the migration and > > then be fully executed on destination? > >=20 >=20 > And so we would need to teach SLOF to try H_CAS again until it stops > returning H_BUSY ? It seems safer to migrate the CAS reboot flag IMHO. >=20 Ok I've tried that with a patched SLOF that sleeps 500ms and tries CAS again if H_BUSY was returned. It fixes the issue but it looks a bit ugly because of the polling with an arbitrary timeout in SLOF... I'm not very comfortable either with calling migration_is_active() from the CAS code in QEMU. David, Any suggestion ? > > Thanks, > > Laurent > >=20 >=20