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 7DEEAC433DF for ; Wed, 15 Jul 2020 15:03:40 +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 46C3E206D5 for ; Wed, 15 Jul 2020 15:03:40 +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="fE+/HjE4" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 46C3E206D5 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]:37938 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jviwc-0006Eg-5Y for qemu-devel@archiver.kernel.org; Wed, 15 Jul 2020 11:03:39 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35056) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jvivG-0004qv-3G for qemu-devel@nongnu.org; Wed, 15 Jul 2020 11:02:14 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:34877 helo=us-smtp-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 1jvivD-0004YG-6z for qemu-devel@nongnu.org; Wed, 15 Jul 2020 11:02:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594825329; 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; bh=Uj+wU0mt1sV/8iDUjmjhd8DVIOts9z0ermRz2cyLVM4=; b=fE+/HjE4q3TbW6N5/TsgFZcaT7iyWWm+myJ2UTYdhOXIU78V1r2Kq/gZ+Bq5osAKM+V8PJ jmWVPEKGvX9r2XpLaNBPWGymM4rVjwtItsYZ5bIa10d+XAQB7UmiiVM5nPLmCEepxMpxP1 vDCdpNoevYtYAd0Hpa9qB52zWo33w08= 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-124-ymEWgwn-Otigy6_o9e8icw-1; Wed, 15 Jul 2020 11:02:06 -0400 X-MC-Unique: ymEWgwn-Otigy6_o9e8icw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F264F8027FB; Wed, 15 Jul 2020 15:02:05 +0000 (UTC) Received: from starship.redhat.com (unknown [10.35.206.178]) by smtp.corp.redhat.com (Postfix) with ESMTP id E7FDF710D6; Wed, 15 Jul 2020 15:02:00 +0000 (UTC) From: Maxim Levitsky To: qemu-devel@nongnu.org Subject: [PATCH v3 0/7] Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread Date: Wed, 15 Jul 2020 18:01:52 +0300 Message-Id: <20200715150159.95050-1-mlevitsk@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=205.139.110.120; envelope-from=mlevitsk@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/15 02:37:05 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 , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , Eduardo Habkost , "Michael S. Tsirkin" , Maxim Levitsky , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi!=0D =0D This is a patch series that is a result of my discussion with Paulo on=0D how to correctly fix the root cause of the BZ #1812399.=0D =0D The root cause of this bug is the fact that IO thread is running mostly=0D unlocked versus main thread on which device hotplug is done.=0D =0D qdev_device_add first creates the device object, then places it on the bus,= =0D and only then realizes it.=0D =0D However some drivers and currently only virtio-scsi enumerate its child bus= =0D devices on each request that is received from the guest and that can happen= on the IO=0D thread.=0D =0D Thus we have a window when new device is on the bus but not realized and ca= n be accessed=0D by the virtio-scsi driver in that state.=0D =0D Fix that by doing two things:=0D =0D 1. Add partial RCU protection to the list of a bus's child devices.=0D This allows the scsi IO thread to safely enumerate the child devices=0D while it races with the hotplug placing the device on the bus.=0D =0D 2. Make the virtio-scsi driver check .realized property of the scsi device= =0D and avoid touching the device if it isn't=0D =0D Note that in the particular bug report the issue wasn't a race but rather d= ue=0D to combination of things, the .realize code in the middle managed to trigge= r IO on the virtqueue=0D which caused the virtio-scsi driver to access the half realized device. How= ever=0D since this can happen as well with real IO thread, this patch series was do= ne,=0D which fixes this as well.=0D =0D Changes from V1:=0D * Patch 2 is new, as suggested by Stefan, added drain_call_rcu() to fix t= he failing unit test,=0D make check pass now=0D =0D * Patches 6,7 are new as well: I added scsi_device_get as suggested by St= efan as well, although=0D this is more a refactoring that anything else as it doesn't solve=0D an existing race.=0D =0D * Addressed most of the review feedback from V1=0D - still need to decide if we need QTAILQ_FOREACH_WITH_RCU_READ_LOCK=0D =0D Changes from V2:=0D =0D * No longer RFC=0D * Addressed most of the feedback from Stefan=0D * Fixed reference count leak in patch 7 when device is about to be unreal= ized=0D * Better testing=0D =0D This series was tested by adding a virtio-scsi drive with iothread,=0D then running fio stress job in the guest in a loop, and then adding/removin= g=0D the scsi drive on the host in the loop.=0D This test was failing usually on 1st iteration withouth this patch series,= =0D and now it seems to work smoothly.=0D =0D Best regards,=0D =09Maxim Levitsky=0D =0D Maxim Levitsky (7):=0D scsi/scsi_bus: switch search direction in scsi_device_find=0D Implement drain_call_rcu and use it in hmp_device_del=0D device-core: use RCU for list of childs of a bus=0D device-core: use atomic_set on .realized property=0D virtio-scsi: don't touch scsi devices that are not yet realized or=0D about to be un-realized=0D scsi: Add scsi_device_get=0D virtio-scsi: use scsi_device_get=0D =0D hw/core/bus.c | 28 +++++++++++++--------=0D hw/core/qdev.c | 56 +++++++++++++++++++++++++++++++-----------=0D hw/scsi/scsi-bus.c | 48 +++++++++++++++++++++++++++++++-----=0D hw/scsi/virtio-scsi.c | 47 ++++++++++++++++++++++++++++-------=0D include/hw/qdev-core.h | 11 +++++++++=0D include/hw/scsi/scsi.h | 2 ++=0D include/qemu/rcu.h | 1 +=0D qdev-monitor.c | 22 +++++++++++++++++=0D util/rcu.c | 55 +++++++++++++++++++++++++++++++++++++++++=0D 9 files changed, 230 insertions(+), 40 deletions(-)=0D =0D --=20=0D 2.26.2=0D =0D