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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 42F5AC433B4 for ; Thu, 8 Apr 2021 14:13:40 +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 8FCC961132 for ; Thu, 8 Apr 2021 14:13:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8FCC961132 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]:53226 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lUVPe-0002oN-Ef for qemu-devel@archiver.kernel.org; Thu, 08 Apr 2021 10:13:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40716) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lUVN0-0007jK-Ao for qemu-devel@nongnu.org; Thu, 08 Apr 2021 10:10:54 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:57422) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lUVMn-0001wc-9R for qemu-devel@nongnu.org; Thu, 08 Apr 2021 10:10:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617891039; 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: in-reply-to:in-reply-to:references:references; bh=u3/zusNK5SRbMrDodIu2zj2+HWUbx98GJ00vRCsH0us=; b=VZ1xTN1H3MEmSIEnvHC3t7ApmEJJmzvZV6QibZGWRcCtEK4+6d8Rum8h8FoCHZq0FFQMkJ ZBkzB6Nn/NMjJCH3IgCfOpf+G6HwTL1lCRXB+2cPKVyzZEtOGTmJC0zwnri7iWMJtwh8Z7 prqY5ysVH7tEZY5A4oU6rvUFGhN2MEI= 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-269-vz0dkep6O8mdt0hsa4Wa8A-1; Thu, 08 Apr 2021 10:10:35 -0400 X-MC-Unique: vz0dkep6O8mdt0hsa4Wa8A-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6B664C73A4; Thu, 8 Apr 2021 14:10:34 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-114-17.ams2.redhat.com [10.36.114.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 186D310016F4; Thu, 8 Apr 2021 14:10:34 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 8E639113525D; Thu, 8 Apr 2021 16:10:31 +0200 (CEST) From: Markus Armbruster To: Thomas Lamprecht Subject: Re: [PATCH v2] monitor/qmp: fix race on CHR_EVENT_CLOSED without OOB References: <20210322154024.15011-1-s.reiter@proxmox.com> <87lf9tces9.fsf@dusky.pond.sub.org> <871rblaqm9.fsf@dusky.pond.sub.org> <1f326b87-b568-5aa5-011e-057e046c0717@proxmox.com> Date: Thu, 08 Apr 2021 16:10:31 +0200 In-Reply-To: <1f326b87-b568-5aa5-011e-057e046c0717@proxmox.com> (Thomas Lamprecht's message of "Thu, 8 Apr 2021 15:27:51 +0200") Message-ID: <87tuog98a0.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action 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: Kevin Wolf , Paolo Bonzini , Stefan Reiter , qemu-devel@nongnu.org, Wolfgang Bumiller Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Thomas Lamprecht writes: > On 08.04.21 14:49, Markus Armbruster wrote: >> Kevin Wolf writes: >>> Am 08.04.2021 um 11:21 hat Markus Armbruster geschrieben: >>>> Should this go into 6.0? >>> >>> This is something that the responsible maintainer needs to decide. >> >> Yes, and that's me. I'm soliciting opinions. >> >>> If it helps you with the decision, and if I understand correctly, it is >>> a regression from 5.1, but was already broken in 5.2. >> >> It helps. >> >> Even more helpful would be a risk assessment: what's the risk of >> applying this patch now vs. delaying it? > > Stefan is on vacation this week, but I can share some information, maybe it > helps. > >> >> If I understand Stefan correctly, Proxmox observed VM hangs. How >> frequent are these hangs? Did they result in data corruption? > > > They were not highly frequent, but frequent enough to get roughly a bit over a > dozen of reports in our forum, which normally means something is off but its > limited to certain HW, storage-tech used or load patterns. > > We had initially a hard time to reproduce this, but a user finally could send > us a backtrace of a hanging VM and with that information we could pin it enough > down and Stefan came up with a good reproducer (see v1 of this patch). Excellent work, props! > We didn't got any report of actual data corruption due to this, but the VM > hangs completely, so a user killing it may produce that theoretical; but only > for those program running in the guest that where not made power-loss safe > anyway... > >> >> How confident do we feel about the fix? >> > > Cannot comment from a technical POV, but can share the feedback we got with it. > > Some context about reach: > We have rolled the fix out to all repository stages which had already a build of > 5.2, that has a reach of about 100k to 300k installations, albeit we only have > some rough stats about the sites that accesses the repository daily, cannot really > tell who actually updated to the new versions, but there are some quite update-happy > people in the community, so with that in mind and my experience of the feedback > loop of rolling out updates, I'd figure a lower bound one can assume without going > out on a limb is ~25k. > > Positive feedback from users: > We got some positive feedback from people which ran into this at least once per > week about the issue being fixed with that. In total almost a dozen user reported > improvements, a good chunk of those which reported the problem in the first place. > > Mixed feedback: > We had one user which reported still getting QMP timeouts, but that their VMs did > not hang anymore (could be high load or the like). Only one user reported that it > did not help, still investigating there, they have quite high CPU pressure stats > and it actually may also be another issue, cannot tell for sure yet though. > > Negative feedback: > We had no new users reporting of new/worse problems in that direction, at least > from what I'm aware off. > > Note, we do not use OOB currently, so above does not speak for the OOB case at > all. Thanks!