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.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 8F263C77B73 for ; Tue, 2 May 2023 18:56:46 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.528780.822345 (Exim 4.92) (envelope-from ) id 1ptvAy-00005r-Pb; Tue, 02 May 2023 18:56:36 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 528780.822345; Tue, 02 May 2023 18:56:36 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ptvAy-00005k-MN; Tue, 02 May 2023 18:56:36 +0000 Received: by outflank-mailman (input) for mailman id 528780; Tue, 02 May 2023 18:56:34 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1ptvAw-0008UA-N0 for xen-devel@lists.xenproject.org; Tue, 02 May 2023 18:56:34 +0000 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by se1-gles-sth1.inumbo.com (Halon) with ESMTPS id 0ddd27c4-e91b-11ed-b225-6b7b168915f2; Tue, 02 May 2023 20:56:33 +0200 (CEST) Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-297-hz_-_nNRNHKLUa7zat10Kw-1; Tue, 02 May 2023 14:56:28 -0400 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id AF841811E7C; Tue, 2 May 2023 18:56:27 +0000 (UTC) Received: from localhost (unknown [10.39.192.230]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5A29F492B03; Tue, 2 May 2023 18:56:26 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 0ddd27c4-e91b-11ed-b225-6b7b168915f2 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683053792; 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=JvqiB11pwfyb9mMlyyPXLE6NQZxd1luK1o/19K1fqnk=; b=Jl4gsC1KlQMRK0juJOoLPeJbdKQyXa0ar5TmsH51hUb7c8IzyFWx7oVpcQ7KsZ9fLU7e1y FFDf3I/nseYyoInDjLMk+EgL4IQGvKr/69RhcjVt0ePFUCGVC9phJK8ASvlRD0ivqxXZWi yTiPIzIo+9+GB2mMV5BEfCF3edfSXxs= X-MC-Unique: hz_-_nNRNHKLUa7zat10Kw-1 Date: Tue, 2 May 2023 14:56:24 -0400 From: Stefan Hajnoczi To: Kevin Wolf Cc: qemu-devel@nongnu.org, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Juan Quintela , Julia Suvorova , xen-devel@lists.xenproject.org, eesposit@redhat.com, Richard Henderson , Fam Zheng , "Michael S. Tsirkin" , Coiby Xu , David Woodhouse , Marcel Apfelbaum , Peter Lieven , Paul Durrant , "Richard W.M. Jones" , qemu-block@nongnu.org, Stefano Garzarella , Anthony Perard , Stefan Weil , Xie Yongji , Paolo Bonzini , Aarushi Mehta , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Eduardo Habkost , Stefano Stabellini , Hanna Reitz , Ronnie Sahlberg , Daniil Tatianin Subject: Re: [PATCH v4 03/20] virtio-scsi: avoid race between unplug and transport event Message-ID: <20230502185624.GA535070@fedora> References: <20230425172716.1033562-1-stefanha@redhat.com> <20230425172716.1033562-4-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Qd9ljEEGWct7+HKe" Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 --Qd9ljEEGWct7+HKe Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, May 02, 2023 at 05:19:46PM +0200, Kevin Wolf wrote: > Am 25.04.2023 um 19:26 hat Stefan Hajnoczi geschrieben: > > Only report a transport reset event to the guest after the SCSIDevice > > has been unrealized by qdev_simple_device_unplug_cb(). > >=20 > > qdev_simple_device_unplug_cb() sets the SCSIDevice's qdev.realized field > > to false so that scsi_device_find/get() no longer see it. > >=20 > > scsi_target_emulate_report_luns() also needs to be updated to filter out > > SCSIDevices that are unrealized. > >=20 > > These changes ensure that the guest driver does not see the SCSIDevice > > that's being unplugged if it responds very quickly to the transport > > reset event. > >=20 > > Reviewed-by: Paolo Bonzini > > Reviewed-by: Michael S. Tsirkin > > Reviewed-by: Daniil Tatianin > > Signed-off-by: Stefan Hajnoczi >=20 > > @@ -1082,6 +1073,15 @@ static void virtio_scsi_hotunplug(HotplugHandler= *hotplug_dev, DeviceState *dev, > > blk_set_aio_context(sd->conf.blk, qemu_get_aio_context(), NULL= ); > > virtio_scsi_release(s); > > } > > + > > + if (virtio_vdev_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG)) { > > + virtio_scsi_acquire(s); > > + virtio_scsi_push_event(s, sd, > > + VIRTIO_SCSI_T_TRANSPORT_RESET, > > + VIRTIO_SCSI_EVT_RESET_REMOVED); > > + scsi_bus_set_ua(&s->bus, SENSE_CODE(REPORTED_LUNS_CHANGED)); > > + virtio_scsi_release(s); > > + } > > } >=20 > s, sd and s->bus are all unrealized at this point, whereas before this > patch they were still realized. I couldn't find any practical problem > with it, but it made me nervous enough that I thought I should comment > on it at least. >=20 > Should we maybe have documentation on these functions that says that > they accept unrealized objects as their parameters? s is the VirtIOSCSI controller, not the SCSIDevice that is being unplugged. The VirtIOSCSI controller is still realized. s->bus is the VirtIOSCSI controller's bus, it is still realized. You are right that the SCSIDevice (sd) has been unrealized at this point: - sd->conf.blk is safe because qdev properties stay alive the Object is deleted, but I'm not sure we should rely on that. - virti_scsi_push_event(.., sd, ...) is questionable because the LUN that's fetched from sd no longer belongs to the unplugged SCSIDevice. How about I change the code to fetch sd->conf.blk and the LUN before unplugging? Stefan --Qd9ljEEGWct7+HKe Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmRRXNgACgkQnKSrs4Gr c8ipsAf+MYIOWS+2lk+xRt3nEDpVri7B1MaNSrlKDWSw2vK6J34jE0bGdHF3I5kZ cS6XFEpcK0BRYes0zRpFZyksJFYS1033b2up4HGodKOJp34ahYy7Vg4yNrov6pzO pZHJAEeEkK0FrHHJkho15qjoOykxt4bib6RzUFN+EdKo3KGQzk1dEyh8fzPEm40x CwNN7D/FJAOOM3CpgsHLUGu6EvOBlfGkd8kS7It3qOD+/BeLFHKDiLBaU5w/IXtA WmgFKnZiOEsMQIEIFgcg+m/YrlomPy0kRPFFSFNn7/5yCmhLCU5WNY/1sTiM3LEi 20aCYTqXQJt5E6c1jk1x21IACc9qRA== =PP5I -----END PGP SIGNATURE----- --Qd9ljEEGWct7+HKe--