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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 3E2C1C433DB for ; Fri, 12 Mar 2021 09:24:01 +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 D7D7164EBB for ; Fri, 12 Mar 2021 09:24:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D7D7164EBB 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]:58842 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lKe1Y-0001oI-0G for qemu-devel@archiver.kernel.org; Fri, 12 Mar 2021 04:24:00 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:51820) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lKe0E-00007E-Oy for qemu-devel@nongnu.org; Fri, 12 Mar 2021 04:22:38 -0500 Received: from us-smtp-delivery-44.mimecast.com ([207.211.30.44]:24241) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lKe0C-0003xV-Oe for qemu-devel@nongnu.org; Fri, 12 Mar 2021 04:22:38 -0500 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-391-WloVzSO6NmuNRIa17LPhfQ-1; Fri, 12 Mar 2021 04:22:24 -0500 X-MC-Unique: WloVzSO6NmuNRIa17LPhfQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DE8151898286; Fri, 12 Mar 2021 09:22:23 +0000 (UTC) Received: from bahia.redhat.com (ovpn-113-236.ams2.redhat.com [10.36.113.236]) by smtp.corp.redhat.com (Postfix) with ESMTP id 805F260C9B; Fri, 12 Mar 2021 09:22:13 +0000 (UTC) From: Greg Kurz To: qemu-devel@nongnu.org Subject: [PATCH v2 0/7] virtiofsd: Avoid potential deadlocks Date: Fri, 12 Mar 2021 10:22:05 +0100 Message-Id: <20210312092212.782255-1-groug@kaod.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=groug@kaod.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kaod.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: softfail client-ip=207.211.30.44; envelope-from=groug@kaod.org; helo=us-smtp-delivery-44.mimecast.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_SOFTFAIL=0.665 autolearn=no 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: =?UTF-8?q?Daniel=20P=20=2E=20Berrang=C3=A9?= , "Michael S. Tsirkin" , "Dr. David Alan Gilbert" , Greg Kurz , virtio-fs@redhat.com, Stefan Hajnoczi , Vivek Goyal Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" A deadlock condition potentially exists if a vhost-user process needs=0D to request something to QEMU on the slave channel while processing a=0D vhost-user message.=0D =0D This doesn't seem to affect any vhost-user implementation so far, but=0D this is currently biting the upcoming enablement of DAX with virtio-fs.=0D The issue is being observed when the guest does an emergency reboot while= =0D a mapping still exits in the DAX window, which is very easy to get with=0D a busy enough workload (e.g. as simulated by blogbench [1]) :=0D =0D - QEMU sends VHOST_USER_GET_VRING_BASE to virtiofsd.=0D =0D - In order to complete the request, virtiofsd then asks QEMU to remove=0D the mapping on the slave channel.=0D =0D All these dialogs are synchronous, hence the deadlock.=0D =0D Another deadlock condition exists in the virtiofsd code itself, related=0D to the use of the vu_dispatch rwlock.=0D =0D This series supercedes Vivek's previous tentative [1] to fix the deadlocks.= =0D Basically, instead of introducing new vhost-user protocol message to=0D specifically shutdown the slave channel, this series introduces a nested=0D event loop in vhost_user_read() as suggested by Stefan Hajnoczi. This=0D allows to monitor and service requests on the slave channel while=0D waiting for virtiofsd to answer to a vhost-user request.=0D =0D This was tested with the latest DAX patchset posted to the virtio-fs=0D list [2], rebased on top of the present series [3]. Testing scenario=0D is:=0D 1) start VM with DAX capable vhost-user-fs device=0D 2) mount -o dax in the guest=0D 3) run Blogbench [4] in virtiofs mount=0D 4) wait 10s, which is enough to have active mappings=0D 5) echo b > /proc/sysrq-trigger=0D 6) wait for the guest to reboot and start over from step 2=0D =0D Without this series, only a couple of reboots ( < 5) are needed to=0D hit a deadlock. With this series applied, an overnight test could=0D reboot the guest 1500+ times without any issues.=0D =0D [1] https://listman.redhat.com/archives/virtio-fs/2021-January/msg00073.htm= l=0D =0D [2] https://listman.redhat.com/archives/virtio-fs/2021-February/msg00058.ht= ml=0D =0D [3] Tree with this series + DAX available at:=0D =0D https://gitlab.com/gkurz/qemu/-/commits/virtio-fs-dax-no-deadlock=0D =0D [4] https://github.com/jedisct1/Blogbench=0D =0D Changes since v2:=0D - added some preliminary fixes and cleanups for the slave channel code=0D - re-factored some code and addressed comments (see individual patches)=0D - more testing=0D =0D Greg Kurz (7):=0D vhost-user: Drop misleading EAGAIN checks in slave_read()=0D vhost-user: Fix double-close on slave_read() error path=0D vhost-user: Factor out duplicated slave_fd teardown code=0D vhost-user: Convert slave channel to QIOChannelSocket=0D vhost-user: Introduce nested event loop in vhost_user_read()=0D vhost-user: Monitor slave channel in vhost_user_read()=0D virtiofsd: Release vu_dispatch_lock when stopping queue=0D =0D hw/virtio/vhost-user.c | 217 +++++++++++++++++++++-------------=0D tools/virtiofsd/fuse_virtio.c | 6 +=0D 2 files changed, 144 insertions(+), 79 deletions(-)=0D =0D --=20=0D 2.26.2=0D =0D