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 7B954C00140 for ; Mon, 8 Aug 2022 15:44:43 +0000 (UTC) Received: from localhost ([::1]:42978 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oL4vq-00058O-3O for qemu-devel@archiver.kernel.org; Mon, 08 Aug 2022 11:44:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38748) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oL4uc-0003pv-IJ for qemu-devel@nongnu.org; Mon, 08 Aug 2022 11:43:28 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:38958) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oL4uY-0005f9-Mt for qemu-devel@nongnu.org; Mon, 08 Aug 2022 11:43:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659973401; 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=rgAXWkABgHpbkMpXBwUm4txpPv8+oh9HiE7cqn7oa/E=; b=FL9W0GVTqb8M/XxgOcqELLManw54yAvJtkfEG9148bDQ6mWC1cOPBVjfAd9ZrThUlWcQHP CAaoE97rjyPZd6NFX/cLBccqGoFRFOTsIFBofGN1j+QWFzHnceNhhhwpuSMGhG79rleKHY fGhckcHLGBzQu4WkFEqhAkNrNyHES54= 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-563-Te17-4s_O7KfI8Hiy7Y-JA-1; Mon, 08 Aug 2022 11:43:14 -0400 X-MC-Unique: Te17-4s_O7KfI8Hiy7Y-JA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9894885A587; Mon, 8 Aug 2022 15:43:13 +0000 (UTC) Received: from localhost (unknown [10.39.194.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0A4232026D4C; Mon, 8 Aug 2022 15:43:12 +0000 (UTC) Date: Mon, 8 Aug 2022 11:43:11 -0400 From: Stefan Hajnoczi To: Emanuele Giuseppe Esposito Cc: qemu-block@nongnu.org, Kevin Wolf , Hanna Reitz , "Michael S. Tsirkin" , Paolo Bonzini , Fam Zheng , qemu-devel@nongnu.org Subject: Re: [PATCH 1/2] virtio-scsi: replace VirtIOBlock dataplane_{start/starting/stopped} with enum Message-ID: References: <20220808094147.612472-1-eesposit@redhat.com> <20220808094147.612472-2-eesposit@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="SOVyBfCcl8XDzMt3" Content-Disposition: inline In-Reply-To: <20220808094147.612472-2-eesposit@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 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_LOW=-0.7, 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" --SOVyBfCcl8XDzMt3 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Aug 08, 2022 at 05:41:46AM -0400, Emanuele Giuseppe Esposito wrote: > Simplify the various dataplane stages in dataplane_start/stop by using > a single enum instead of having multiple flags. >=20 > Read/write the enum atomically, as it can be read also by iothread > callbacks. What guarantees that these relaxed loads/stores always produce DATAPLANE_STARTING/STARTED in virtio_scsi_defer_to_dataplane() and not an older value? Are there implicit memory barriers? >=20 > Signed-off-by: Emanuele Giuseppe Esposito > --- > hw/scsi/virtio-scsi-dataplane.c | 21 +++++++++------------ > hw/scsi/virtio-scsi.c | 10 ++++++---- > include/hw/virtio/virtio-scsi.h | 5 ++--- > include/hw/virtio/virtio.h | 7 +++++++ > 4 files changed, 24 insertions(+), 19 deletions(-) >=20 > diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-datapl= ane.c > index a575c3f0cd..9ad73e3e19 100644 > --- a/hw/scsi/virtio-scsi-dataplane.c > +++ b/hw/scsi/virtio-scsi-dataplane.c > @@ -106,13 +106,12 @@ int virtio_scsi_dataplane_start(VirtIODevice *vdev) > VirtIOSCSICommon *vs =3D VIRTIO_SCSI_COMMON(vdev); > VirtIOSCSI *s =3D VIRTIO_SCSI(vdev); > =20 > - if (s->dataplane_started || > - s->dataplane_starting || > + if (qatomic_read(&s->dataplane_state) <=3D DATAPLANE_STARTED || It's not obvious that the STOPPING and STOPPED constants have a value greater than STARTING and STARTED. It could be other way around too. It would be safer to write the code so there are no assumptions about the constants: VirtIODataplaneStates state =3D qatomic_read(&s->dataplane_state); if (state =3D=3D DATAPLANE_STARTING || state =3D=3D DATAPLANE_STARTED || = =2E..) --SOVyBfCcl8XDzMt3 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmLxLw8ACgkQnKSrs4Gr c8hu8Qf/foIr3g4D9m12SF0rpFHo2U08QWCwLRK6bqTgm8skvOjfIAqXa/7GCJPc SaYQu+EdQLdhimff5hJL56Px7J1cWWOX3dl3AxvBuCxS7W9DaH+4CgltaTTw2mvd RVMp2XYeSWfqiEiHe2nXm1k9VGQ6VpRCuprgaYIjBrBWNn44BsLrVqBODu5KRWw8 aYkIhitsJAu06dSX4zsezKMuNNmPLbEWgj1qD/GYp3NDF5GyZthbtEnJsJm+x899 bBwkw4qtEn/nZNENfial+PkOyKmDjd7KQD7rwoxcV7Iode7MQwSRI13TKalRT4Sl Mpx6HNAXDf/Gygmgl3PSCHYR0Oggig== =AI66 -----END PGP SIGNATURE----- --SOVyBfCcl8XDzMt3--