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 77561C433E2 for ; Mon, 31 Aug 2020 15:04:37 +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 2B401207EA for ; Mon, 31 Aug 2020 15:04:37 +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="aVyeELYj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2B401207EA 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]:40532 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kClMK-0001wr-7w for qemu-devel@archiver.kernel.org; Mon, 31 Aug 2020 11:04:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44150) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kClJS-00069l-3R for qemu-devel@nongnu.org; Mon, 31 Aug 2020 11:01:39 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:23409) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kClJP-0004Tt-6t for qemu-devel@nongnu.org; Mon, 31 Aug 2020 11:01:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1598886093; 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=RJRT4zHeLM58IQVPnpfioQsjElJ0yxpdl4WV4GBXRK8=; b=aVyeELYjFDv0xPTDUezewVkP3bUHjgRcMDtr3DGUuJR7cqyuw+NO0QZ+bSQjanck9LvriC ZPIHRGQ72L+i3T3+F+wWylT5aHuvM8XJWFjCRX4sRmCnCrtw5Uc0hG3QfB/r9at6fiLyaq Hvhjxa3sgzrTMSm7CWQHtGyStmIiCOU= 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-490-ti5QzDIzPgym0fOGj2x3PA-1; Mon, 31 Aug 2020 11:01:31 -0400 X-MC-Unique: ti5QzDIzPgym0fOGj2x3PA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7F2D118A2242; Mon, 31 Aug 2020 15:01:30 +0000 (UTC) Received: from localhost.localdomain (unknown [10.35.206.190]) by smtp.corp.redhat.com (Postfix) with ESMTP id 729BE19C4F; Mon, 31 Aug 2020 15:01:25 +0000 (UTC) From: Maxim Levitsky To: qemu-devel@nongnu.org Subject: [PATCH v4 0/9] Fix scsi devices plug/unplug races w.r.t virtio-scsi iothread Date: Mon, 31 Aug 2020 18:01:15 +0300 Message-Id: <20200831150124.206267-1-mlevitsk@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com X-Mimecast-Spam-Score: 0.003 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=63.128.21.124; envelope-from=mlevitsk@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/31 03:02:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, 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. Let scsi_device_find not return devices that are on the bus but not real= ized=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 V3:=0D =0D * Rebased to latest qemu=0D =0D * Added a new patch to fix related race in scsi_target_emulate_report_luns= =0D =0D * Moved the non-realized device check to scsi core, since there is no=0D way a device driver will want to see non realized devices on a scsi bus.= =0D (scsi-bus still needs this and can using an internal function)=0D =0D * Splitted patch that added drain_rcu and used it, to patch that only adds = it, and one=0D that uses it (no other changes so I kept Reviewed-by)=0D =0D *Some tweaks to commits=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 (9):=0D scsi/scsi_bus: switch search direction in scsi_device_find=0D rcu: Implement drain_call_rcu=0D device_core: use drain_call_rcu in in hmp_device_del/qmp_device_add=0D device-core: use RCU for list of childs of a bus=0D device-core: use atomic_set on .realized property=0D scsi/scsi-bus: scsi_device_find: don't return unrealized devices=0D scsi/scsi_bus: Add scsi_device_get=0D virtio-scsi: use scsi_device_get=0D scsi/scsi_bus: fix races in REPORT LUNS=0D =0D hw/core/bus.c | 28 +++++---=0D hw/core/qdev.c | 56 +++++++++++----=0D hw/scsi/scsi-bus.c | 151 ++++++++++++++++++++++++++---------------=0D hw/scsi/virtio-scsi.c | 27 +++++---=0D include/hw/qdev-core.h | 11 +++=0D include/hw/scsi/scsi.h | 1 +=0D include/qemu/rcu.h | 1 +=0D qdev-monitor.c | 22 ++++++=0D util/rcu.c | 55 +++++++++++++++=0D 9 files changed, 265 insertions(+), 87 deletions(-)=0D =0D --=20=0D 2.26.2=0D =0D