From nobody Wed Nov 27 08:42:10 2024 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1700069271318504.7512871162594; Wed, 15 Nov 2023 09:27:51 -0800 (PST) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r3Jfx-0006D2-Tu; Wed, 15 Nov 2023 12:27:42 -0500 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 1r3Jfu-00064m-UQ; Wed, 15 Nov 2023 12:27:39 -0500 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r3Jfr-0007kn-B9; Wed, 15 Nov 2023 12:27:38 -0500 Received: from [2001:8b0:10b:1::ebe] (helo=i7.infradead.org) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1r3Jfi-004Bc1-25; Wed, 15 Nov 2023 17:27:26 +0000 Received: from dwoodhou by i7.infradead.org with local (Exim 4.96.2 #2 (Red Hat Linux)) id 1r3Jfh-004sFD-0h; Wed, 15 Nov 2023 17:27:25 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description; bh=nb4/k2mDzWcTB0WCWH1Sc4XyVKQa4fT5IUZadSOtr3A=; b=lHv8bWujGEmJl9ObnRZwBoZQPl gX7tpE1PWf5bAAP/UlMIQIio4a2+QZqHthuG5aA3qkM2vZGDvL5XqQUXCoSnzqjPG6NHqUcj4pj5b Mj1nNHARxT6exhbrY5ga6H1FrO8o05cTq5+WWJBFm91uuwEnQ8EzHGWimoZinGk1cdhlBAqqsZ5QL GPDIhHeAok8hk8s6DJUXW2FudVHzasFQHMao+kuK0m5SZB2wF4CID3aUheWtD2zRHP/ntD05fSCB4 2a9vXKFFmi34fk5gkSWR/cPvRHT6ChZ5j7eOKvGC2SWcvDE6xX9s9ZZtt2nGZUNY0T+3jH3tZZzZM gAVhOqKA==; From: David Woodhouse To: qemu-devel@nongnu.org Cc: Stefano Stabellini , Anthony Perard , Paul Durrant , Kevin Wolf , Hanna Reitz , Jason Wang , Paolo Bonzini , xen-devel@lists.xenproject.org, qemu-block@nongnu.org Subject: [PATCH 1/3] net: do not delete nics in net_cleanup() Date: Wed, 15 Nov 2023 17:24:35 +0000 Message-ID: <20231115172723.1161679-2-dwmw2@infradead.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231115172723.1161679-1-dwmw2@infradead.org> References: <20231115172723.1161679-1-dwmw2@infradead.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: none client-ip=2001:8b0:10b:1:d65d:64ff:fe57:4e05; envelope-from=BATV+a72437c23eaab18a7e37+7388+infradead.org+dwmw2@desiato.srs.infradead.org; helo=desiato.infradead.org X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_NONE=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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZM-MESSAGEID: 1700069272642100007 Content-Type: text/plain; charset="utf-8" From: David Woodhouse In net_cleanup() we only need to delete the netdevs, as those may have state which outlives Qemu when it exits, and thus may actually need to be cleaned up on exit. The nics, on the other hand, are owned by the device which created them. Most devices don't bother to clean up on exit because they don't have any state which will outlive Qemu... but XenBus devices do need to clean up their nodes in XenStore, and do have an exit handler to delete them. When the XenBus exit handler destroys the xen-net-device, it attempts to delete its nic after net_cleanup() had already done so. And crashes. Fix this by only deleting netdevs as we walk the list. As the comment notes, we can't use QTAILQ_FOREACH_SAFE() as each deletion may remove *multiple* entries, including the "safely" saved 'next' pointer. But we can store the *previous* entry, since nics are safe. Signed-off-by: David Woodhouse Reviewed-by: Paul Durrant --- net/net.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) diff --git a/net/net.c b/net/net.c index c0c0cbe99e..bbe33da176 100644 --- a/net/net.c +++ b/net/net.c @@ -1499,18 +1499,34 @@ static void net_vm_change_state_handler(void *opaqu= e, bool running, =20 void net_cleanup(void) { - NetClientState *nc; + NetClientState *nc, **p =3D &QTAILQ_FIRST(&net_clients); =20 /*cleanup colo compare module for COLO*/ colo_compare_cleanup(); =20 - /* We may del multiple entries during qemu_del_net_client(), - * so QTAILQ_FOREACH_SAFE() is also not safe here. + /* + * Walk the net_clients list and remove the netdevs but *not* any + * NET_CLIENT_DRIVER_NIC entries. The latter are owned by the device + * model which created them, and in some cases (e.g. xen-net-device) + * the device itself may do cleanup at exit and will be upset if we + * just delete its NIC from underneath it. + * + * Since qemu_del_net_client() may delete multiple entries, using + * QTAILQ_FOREACH_SAFE() is not safe here. The only safe pointer + * to keep as a bookmark is a NET_CLIENT_DRIVER_NIC entry, so keep + * 'p' pointing to either the head of the list, or the 'next' field + * of the latest NET_CLIENT_DRIVER_NIC, and operate on *p as we walk + * the list. + * + * The 'nc' variable isn't part of the list traversal; it's purely + * for convenience as too much '(*p)->' has a tendency to make the + * readers' eyes bleed. */ - while (!QTAILQ_EMPTY(&net_clients)) { - nc =3D QTAILQ_FIRST(&net_clients); + while (*p) { + nc =3D *p; if (nc->info->type =3D=3D NET_CLIENT_DRIVER_NIC) { - qemu_del_nic(qemu_get_nic(nc)); + /* Skip NET_CLIENT_DRIVER_NIC entries */ + p =3D &QTAILQ_NEXT(nc, next); } else { qemu_del_net_client(nc); } --=20 2.41.0