From patchwork Wed Oct 25 14:50:34 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Woodhouse X-Patchwork-Id: 13436348 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86A6EC25B47 for ; Wed, 25 Oct 2023 14:51:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344466AbjJYOvp (ORCPT ); Wed, 25 Oct 2023 10:51:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58468 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344485AbjJYOvb (ORCPT ); Wed, 25 Oct 2023 10:51:31 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 890A810DD for ; Wed, 25 Oct 2023 07:51:24 -0700 (PDT) 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=iaeDXSTaoWdCm87GDHXDzDikArDTOfszjp92r6YPQM0=; b=Fpo2lDHmkFJFrEzTxCnYSHMQc+ H+POf4RpTDXrqfi7zmTI2kpkXiZEJ/4ikVugJbl/UXMyulJnl8bxTi7gdq+Xlhe/NOsdTz353nXNS skhnTvQvc19bBykXDJLHjeBVQ97kJvOEjCn3zBqYb/BH5rDtwk6NqQC0EyXGhRuEVDofWOrIuQUbH eDXBfUYpNVxLjOjbdUpmFPsWWBCjffiEX876q5ArcW6FdlTHX93HUMDbaBkhxtxYaZxt/fpHXCNkE Ko/NceL/1GypeXooX+xxhcNkWMbOUUaDd3BrGGwo4s3+7LbNRB/e9K7vIixU+dnx+7J2jpuR7mvKp dd1Vd6Hw==; 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 1qvfDa-00GPM5-1F; Wed, 25 Oct 2023 14:50:51 +0000 Received: from dwoodhou by i7.infradead.org with local (Exim 4.96 #2 (Red Hat Linux)) id 1qvfDZ-002dFL-0k; Wed, 25 Oct 2023 15:50:45 +0100 From: David Woodhouse To: qemu-devel@nongnu.org Cc: Kevin Wolf , Hanna Reitz , Stefano Stabellini , Anthony Perard , Paul Durrant , =?utf-8?q?Marc-Andr=C3=A9_Lureau?= , Paolo Bonzini , "Michael S. Tsirkin" , Marcel Apfelbaum , Richard Henderson , Eduardo Habkost , Jason Wang , Marcelo Tosatti , qemu-block@nongnu.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Bernhard Beschow , Joel Upham Subject: [PATCH v3 20/28] net: do not delete nics in net_cleanup() Date: Wed, 25 Oct 2023 15:50:34 +0100 Message-Id: <20231025145042.627381-21-dwmw2@infradead.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20231025145042.627381-1-dwmw2@infradead.org> References: <20231025145042.627381-1-dwmw2@infradead.org> MIME-Version: 1.0 Sender: David Woodhouse X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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 *opaque, bool running, void net_cleanup(void) { - NetClientState *nc; + NetClientState *nc, **p = &QTAILQ_FIRST(&net_clients); /*cleanup colo compare module for COLO*/ colo_compare_cleanup(); - /* 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 = QTAILQ_FIRST(&net_clients); + while (*p) { + nc = *p; if (nc->info->type == NET_CLIENT_DRIVER_NIC) { - qemu_del_nic(qemu_get_nic(nc)); + /* Skip NET_CLIENT_DRIVER_NIC entries */ + p = &QTAILQ_NEXT(nc, next); } else { qemu_del_net_client(nc); }