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 77D9DEE4993 for ; Tue, 22 Aug 2023 19:35:42 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qYX9p-0005vN-TL; Tue, 22 Aug 2023 15:35:17 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qYX9l-0005p9-97 for qemu-devel@nongnu.org; Tue, 22 Aug 2023 15:35:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qYX9i-0005CU-Pp for qemu-devel@nongnu.org; Tue, 22 Aug 2023 15:35:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1692732908; 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=Sr0AYOB3pFsJotI0XmHXIMmObopaVDUTS+W99no6/ng=; b=IJaLquTRr4Oalqk7frT2thDKBHQT4KN7NHahAsdHR5qQuKAe+vdnoWhgeOYgWPXQIpjbZ2 mETGXvTTSWm78vm0RxbStDdQcPXVbZ+EqBQlZHl6TjY2L5CuI/ZgDnnO6Vo+pU44YutRTt +yCls2TLk/Db2mjRTVaA6/A9x6GkZBQ= 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-339-kCK9oUnsMMiXDPnIe2NuqA-1; Tue, 22 Aug 2023 15:35:04 -0400 X-MC-Unique: kCK9oUnsMMiXDPnIe2NuqA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B94E6858EED; Tue, 22 Aug 2023 19:35:03 +0000 (UTC) Received: from localhost (unknown [10.39.195.69]) by smtp.corp.redhat.com (Postfix) with ESMTP id 50D87C15BAE; Tue, 22 Aug 2023 19:35:03 +0000 (UTC) Date: Tue, 22 Aug 2023 15:35:02 -0400 From: Stefan Hajnoczi To: Kevin Wolf Cc: qemu-block@nongnu.org, eblake@redhat.com, eesposit@redhat.com, pbonzini@redhat.com, vsementsov@yandex-team.ru, qemu-devel@nongnu.org Subject: Re: [PATCH 17/21] block: Take graph rdlock in bdrv_drop_intermediate() Message-ID: <20230822193502.GU727224@fedora> References: <20230817125020.208339-1-kwolf@redhat.com> <20230817125020.208339-18-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ID+33Dwtqxy/1kpi" Content-Disposition: inline In-Reply-To: <20230817125020.208339-18-kwolf@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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: -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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org --ID+33Dwtqxy/1kpi Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Aug 17, 2023 at 02:50:16PM +0200, Kevin Wolf wrote: > The function reads the parents list, so it needs to hold the graph lock. >=20 > Signed-off-by: Kevin Wolf > --- > block.c | 2 ++ > 1 file changed, 2 insertions(+) >=20 > diff --git a/block.c b/block.c > index 7df8780d6e..a82389f742 100644 > --- a/block.c > +++ b/block.c > @@ -5934,9 +5934,11 @@ int bdrv_drop_intermediate(BlockDriverState *top, = BlockDriverState *base, > backing_file_str =3D base->filename; > } > =20 > + bdrv_graph_rdlock_main_loop(); > QLIST_FOREACH(c, &top->parents, next_parent) { > updated_children =3D g_slist_prepend(updated_children, c); > } > + bdrv_graph_rdunlock_main_loop(); This is GLOBAL_STATE_CODE, so why take the read lock? I thought nothing can modify the graph here. If it could, then stashing the parents in the updated_children probably wouldn't be safe anyway. > =20 > /* > * It seems correct to pass detach_subchain=3Dtrue here, but it trig= gers > --=20 > 2.41.0 >=20 --ID+33Dwtqxy/1kpi Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmTlDeYACgkQnKSrs4Gr c8hc6Qf/UrYCUTPc5ZOkOq+9vx/kJwcguQsRy3qCWQidl4fbAqbqDRZApOA6wbV1 tkVSyCM799iKjkeMThMUVotWYV/CR094MmXLVsIVOQdx1au8p8RNcUOxdd7ihnRV dkSDFTGdERW3Z6sdYcOtBu2a56I1uXcosjprbJ18nA4ZKb22kqAdhgkYKgVILIYp R5gAdMVo8dA4S4OkTjBv4BhHvlk0YVlbN3RppjQBm+wjex0c3dpKbKUZYtYft9Nm zfJVqBfHJcSZiCgUsgGpNlJsnrq5FEJS2j92eotUP3DSYY3R5XLPFA3i8xFwyNAu n+HdcLiPg9nruqnchC4CZy3Dg+VXvA== =wSyr -----END PGP SIGNATURE----- --ID+33Dwtqxy/1kpi--