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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 ACC21C433E0 for ; Wed, 29 Jul 2020 19:57:29 +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 76E4320658 for ; Wed, 29 Jul 2020 19:57:29 +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="GsO087li" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 76E4320658 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]:34688 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k0sCe-0004jC-Mv for qemu-devel@archiver.kernel.org; Wed, 29 Jul 2020 15:57:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55352) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k0sBr-0004IE-Kn for qemu-devel@nongnu.org; Wed, 29 Jul 2020 15:56:39 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:43890 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1k0sBp-0007ym-8A for qemu-devel@nongnu.org; Wed, 29 Jul 2020 15:56:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596052592; 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=+XdDXQ90+evBlCxXRfWZJdXeFaDBFjG5pDqxewmhYAY=; b=GsO087liVWKG6eHvnDeadPGP883MJDjEh+9OEaNH+NHH1k7BPK9U3iY3p/7wVROOJxI5H1 VLlW4A8Eol1Hy5hFsMnYWek+gTBrXi2FovVx27pAspmqaq4/v0g6+nc1APK9W/eNrZk2ox WN9h35SOzfcR+L+Pxrvh5nD21qcaMi0= 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-290-RDmmID7SNSK-xMSrNIYr9Q-1; Wed, 29 Jul 2020 15:56:28 -0400 X-MC-Unique: RDmmID7SNSK-xMSrNIYr9Q-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 98C4459; Wed, 29 Jul 2020 19:56:27 +0000 (UTC) Received: from starship (unknown [10.35.206.108]) by smtp.corp.redhat.com (Postfix) with ESMTP id 59EBB6179C; Wed, 29 Jul 2020 19:56:20 +0000 (UTC) Message-ID: Subject: Re: [PATCH v3 0/7] Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread From: Maxim Levitsky To: qemu-devel@nongnu.org Date: Wed, 29 Jul 2020 22:56:19 +0300 In-Reply-To: <20200715150159.95050-1-mlevitsk@redhat.com> References: <20200715150159.95050-1-mlevitsk@redhat.com> User-Agent: Evolution 3.36.3 (3.36.3-1.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=mlevitsk@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/29 09:18:45 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: Fam Zheng , Paolo Bonzini , "Daniel P. =?ISO-8859-1?Q?Berrang=E9?=" , Eduardo Habkost , "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 2020-07-15 at 18:01 +0300, Maxim Levitsky wrote: > Hi! > > This is a patch series that is a result of my discussion with Paulo on > how to correctly fix the root cause of the BZ #1812399. > > The root cause of this bug is the fact that IO thread is running mostly > unlocked versus main thread on which device hotplug is done. > > qdev_device_add first creates the device object, then places it on the bus, > and only then realizes it. > > However some drivers and currently only virtio-scsi enumerate its child bus > devices on each request that is received from the guest and that can happen on the IO > thread. > > Thus we have a window when new device is on the bus but not realized and can be accessed > by the virtio-scsi driver in that state. > > Fix that by doing two things: > > 1. Add partial RCU protection to the list of a bus's child devices. > This allows the scsi IO thread to safely enumerate the child devices > while it races with the hotplug placing the device on the bus. > > 2. Make the virtio-scsi driver check .realized property of the scsi device > and avoid touching the device if it isn't > > Note that in the particular bug report the issue wasn't a race but rather due > to combination of things, the .realize code in the middle managed to trigger IO on the virtqueue > which caused the virtio-scsi driver to access the half realized device. However > since this can happen as well with real IO thread, this patch series was done, > which fixes this as well. > > Changes from V1: > * Patch 2 is new, as suggested by Stefan, added drain_call_rcu() to fix the failing unit test, > make check pass now > > * Patches 6,7 are new as well: I added scsi_device_get as suggested by Stefan as well, although > this is more a refactoring that anything else as it doesn't solve > an existing race. > > * Addressed most of the review feedback from V1 > - still need to decide if we need QTAILQ_FOREACH_WITH_RCU_READ_LOCK > > Changes from V2: > > * No longer RFC > * Addressed most of the feedback from Stefan > * Fixed reference count leak in patch 7 when device is about to be unrealized > * Better testing > > This series was tested by adding a virtio-scsi drive with iothread, > then running fio stress job in the guest in a loop, and then adding/removing > the scsi drive on the host in the loop. > This test was failing usually on 1st iteration withouth this patch series, > and now it seems to work smoothly. > > Best regards, > Maxim Levitsky > > Maxim Levitsky (7): > scsi/scsi_bus: switch search direction in scsi_device_find > Implement drain_call_rcu and use it in hmp_device_del > device-core: use RCU for list of childs of a bus > device-core: use atomic_set on .realized property > virtio-scsi: don't touch scsi devices that are not yet realized or > about to be un-realized > scsi: Add scsi_device_get > virtio-scsi: use scsi_device_get > > hw/core/bus.c | 28 +++++++++++++-------- > hw/core/qdev.c | 56 +++++++++++++++++++++++++++++++----------- > hw/scsi/scsi-bus.c | 48 +++++++++++++++++++++++++++++++----- > hw/scsi/virtio-scsi.c | 47 ++++++++++++++++++++++++++++------- > include/hw/qdev-core.h | 11 +++++++++ > include/hw/scsi/scsi.h | 2 ++ > include/qemu/rcu.h | 1 + > qdev-monitor.c | 22 +++++++++++++++++ > util/rcu.c | 55 +++++++++++++++++++++++++++++++++++++++++ > 9 files changed, 230 insertions(+), 40 deletions(-) > > -- > 2.26.2 > Very gentle ping about this patch series. Best regards, Maxim Levitsky