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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 46986C00140 for ; Fri, 5 Aug 2022 07:14:38 +0000 (UTC) Received: from localhost ([::1]:56904 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oJrXZ-0003pC-1F for qemu-devel@archiver.kernel.org; Fri, 05 Aug 2022 03:14:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53914) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oJrOP-0007lk-GL for qemu-devel@nongnu.org; Fri, 05 Aug 2022 03:05:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:42721) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oJrON-0001fu-C0 for qemu-devel@nongnu.org; Fri, 05 Aug 2022 03:05:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659683106; 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=/WJgRky06xpf2ZG0pyIuBEx4EelQR4THlZHUFkkOWGs=; b=HPog2AK28CJo+bS9q6cpYvMYE+xFo8X+CCEhPmXhsZVHYXtYL3Ibmb9R0DTHAYA4O31Yjo jE84FXtvLiwHaVgze+tg/i/zV0yKiP/2C7iW6VR5MD+8BTTwGYYNlSPED9aOn+f7Qg0Ja4 ycTeWrpsfjfIOAzQhGZCNBscNUnK5ro= Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-518-XLbH8nO_OPmmmUGqhNxLqA-1; Fri, 05 Aug 2022 03:05:05 -0400 X-MC-Unique: XLbH8nO_OPmmmUGqhNxLqA-1 Received: by mail-ed1-f72.google.com with SMTP id c14-20020a05640227ce00b0043e5df12e2cso1031539ede.15 for ; Fri, 05 Aug 2022 00:05:05 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=/WJgRky06xpf2ZG0pyIuBEx4EelQR4THlZHUFkkOWGs=; b=AagRSxkddTBGf10q8ZZzr8FKaua5rnGFplNzborYJpmAt0jpGiWODYJygkK94bjrPG UEeR13g/cSkWxxj7fF2ppC8kBhOhCbh7LMjhQDGuLYwTNbhKpHQUl0/Oofd+q1wcVc5d J/xBSTyYsuJ8Pnso4fPSs806DG33RWAhtcbxibUl/ni5Z/aLC8D2H0Hzua29yjYi37pv 9qIESpEG4hXgNnabp1Of8wzgU3eidkIj5Sc/rVOkihKF1BEDjH9PT+ekLUICVM+g17KP qDkO8Dt5YTASrtQ6o4trZcxfyQ/Lyv4KEIxP8CUZx4ZenfijkB4UvmnAVkLMwh5qiYGm N6rA== X-Gm-Message-State: ACgBeo3IcRpNxn6FuKZDKAiVGnHRf6UD8j6THkR7LSyzHfANPOqGtFn1 EAhm/VnvE/ND5JSO3wKpfMcmCARcnDN+cHvJ1mWk625k9DolT/Ne22y8n00QPt1QbKHWiOo25MD HwRRcH0aXh8lhzWE= X-Received: by 2002:a05:6402:5388:b0:435:71b:5d44 with SMTP id ew8-20020a056402538800b00435071b5d44mr5277753edb.364.1659683104368; Fri, 05 Aug 2022 00:05:04 -0700 (PDT) X-Google-Smtp-Source: AA6agR45hKjOE9LQE79paLRZ6F2f4Sc4gNGFeRqLGL41lTrQgQfC9kSNt0sOI+NwTSalH6p+CMskYA== X-Received: by 2002:a05:6402:5388:b0:435:71b:5d44 with SMTP id ew8-20020a056402538800b00435071b5d44mr5277743edb.364.1659683104137; Fri, 05 Aug 2022 00:05:04 -0700 (PDT) Received: from redhat.com ([2.52.137.185]) by smtp.gmail.com with ESMTPSA id dc2-20020a170906c7c200b007306df330e5sm1274484ejb.12.2022.08.05.00.05.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Aug 2022 00:05:03 -0700 (PDT) Date: Fri, 5 Aug 2022 03:04:59 -0400 From: "Michael S. Tsirkin" To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, sgarzare@redhat.com, kwolf@redhat.com, Emanuele Giuseppe Esposito , Fam Zheng , Paolo Bonzini , Qing Wang Subject: Re: [PATCH] virtio-scsi: fix race in virtio_scsi_dataplane_start() Message-ID: <20220805030329-mutt-send-email-mst@kernel.org> References: <20220803162824.948023-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220803162824.948023-1-stefanha@redhat.com> Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Aug 03, 2022 at 12:28:24PM -0400, Stefan Hajnoczi wrote: > As soon as virtio_scsi_data_plane_start() attaches host notifiers the > IOThread may start virtqueue processing. There is a race between > IOThread virtqueue processing and virtio_scsi_data_plane_start() because > it only assigns s->dataplane_started after attaching host notifiers. > > When a virtqueue handler function in the IOThread calls > virtio_scsi_defer_to_dataplane() it may see !s->dataplane_started and > attempt to start dataplane even though we're already in the IOThread: > > #0 0x00007f67b360857c __pthread_kill_implementation (libc.so.6 + 0xa257c) > #1 0x00007f67b35bbd56 raise (libc.so.6 + 0x55d56) > #2 0x00007f67b358e833 abort (libc.so.6 + 0x28833) > #3 0x00007f67b358e75b __assert_fail_base.cold (libc.so.6 + 0x2875b) > #4 0x00007f67b35b4cd6 __assert_fail (libc.so.6 + 0x4ecd6) > #5 0x000055ca87fd411b memory_region_transaction_commit (qemu-kvm + 0x67511b) > #6 0x000055ca87e17811 virtio_pci_ioeventfd_assign (qemu-kvm + 0x4b8811) > #7 0x000055ca87e14836 virtio_bus_set_host_notifier (qemu-kvm + 0x4b5836) > #8 0x000055ca87f8e14e virtio_scsi_set_host_notifier (qemu-kvm + 0x62f14e) > #9 0x000055ca87f8dd62 virtio_scsi_dataplane_start (qemu-kvm + 0x62ed62) > #10 0x000055ca87e14610 virtio_bus_start_ioeventfd (qemu-kvm + 0x4b5610) > #11 0x000055ca87f8c29a virtio_scsi_handle_ctrl (qemu-kvm + 0x62d29a) > #12 0x000055ca87fa5902 virtio_queue_host_notifier_read (qemu-kvm + 0x646902) > #13 0x000055ca882c099e aio_dispatch_handler (qemu-kvm + 0x96199e) > #14 0x000055ca882c1761 aio_poll (qemu-kvm + 0x962761) > #15 0x000055ca880e1052 iothread_run (qemu-kvm + 0x782052) > #16 0x000055ca882c562a qemu_thread_start (qemu-kvm + 0x96662a) > > This patch assigns s->dataplane_started before attaching host notifiers > so that virtqueue handler functions that run in the IOThread before > virtio_scsi_data_plane_start() returns correctly identify that dataplane > does not need to be started. > > Note that s->dataplane_started does not need the AioContext lock because > it is set before attaching host notifiers and cleared after detaching > host notifiers. In other words, the IOThread always sees the value true > and the main loop thread does not modify it while the IOThread is > active. > > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2099541 > Reported-by: Qing Wang > Signed-off-by: Stefan Hajnoczi A scsi thing that tree seems more appropriate. Reviewed-by: Michael S. Tsirkin > --- > hw/scsi/virtio-scsi-dataplane.c | 33 +++++++++++++++++++++++++-------- > 1 file changed, 25 insertions(+), 8 deletions(-) > > diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c > index 8bb6e6acfc..a575c3f0cd 100644 > --- a/hw/scsi/virtio-scsi-dataplane.c > +++ b/hw/scsi/virtio-scsi-dataplane.c > @@ -66,6 +66,21 @@ static int virtio_scsi_set_host_notifier(VirtIOSCSI *s, VirtQueue *vq, int n) > return 0; > } > > +/* Context: BH in IOThread */ > +static void virtio_scsi_dataplane_start_bh(void *opaque) > +{ > + VirtIOSCSI *s = opaque; > + VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s); > + int i; > + > + virtio_queue_aio_attach_host_notifier(vs->ctrl_vq, s->ctx); > + virtio_queue_aio_attach_host_notifier_no_poll(vs->event_vq, s->ctx); > + > + for (i = 0; i < vs->conf.num_queues; i++) { > + virtio_queue_aio_attach_host_notifier(vs->cmd_vqs[i], s->ctx); > + } > +} > + > /* Context: BH in IOThread */ > static void virtio_scsi_dataplane_stop_bh(void *opaque) > { > @@ -136,16 +151,18 @@ int virtio_scsi_dataplane_start(VirtIODevice *vdev) > > memory_region_transaction_commit(); > > - aio_context_acquire(s->ctx); > - virtio_queue_aio_attach_host_notifier(vs->ctrl_vq, s->ctx); > - virtio_queue_aio_attach_host_notifier_no_poll(vs->event_vq, s->ctx); > - > - for (i = 0; i < vs->conf.num_queues; i++) { > - virtio_queue_aio_attach_host_notifier(vs->cmd_vqs[i], s->ctx); > - } > - > s->dataplane_starting = false; > s->dataplane_started = true; > + > + /* > + * Attach notifiers from within the IOThread. It's possible to attach > + * notifiers from our thread directly but this approach has the advantages > + * that virtio_scsi_dataplane_start_bh() is symmetric with > + * virtio_scsi_dataplane_stop_bh() and the s->dataplane_started assignment > + * above doesn't require explicit synchronization. > + */ > + aio_context_acquire(s->ctx); > + aio_wait_bh_oneshot(s->ctx, virtio_scsi_dataplane_start_bh, s); > aio_context_release(s->ctx); > return 0; > > -- > 2.37.1