From mboxrd@z Thu Jan 1 00:00:00 1970 From: Patrick McHardy Subject: Re: [PATCH 3/3] netdevice: order of synchronization of IFF_PROMISC and IFF_ALLMULTI Date: Mon, 16 Jun 2008 12:03:43 +0200 Message-ID: <48563A7F.50309@trash.net> References: <48562F9A.5030509@cn.fujitsu.com> <485631FF.7040509@trash.net> <485634D1.2010603@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , NETDEV To: Wang Chen Return-path: Received: from stinky.trash.net ([213.144.137.162]:58988 "EHLO stinky.trash.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751000AbYFPKDt (ORCPT ); Mon, 16 Jun 2008 06:03:49 -0400 In-Reply-To: <485634D1.2010603@cn.fujitsu.com> Sender: netdev-owner@vger.kernel.org List-ID: Wang Chen wrote: > Patrick McHardy said the following on 2008-6-16 17:27: >> Wang Chen wrote: >>> - if (dev->flags & IFF_ALLMULTI) >>> - dev_set_allmulti(real_dev, 1); >>> + /* NOTE: order of synchronization of IFF_PROMISC and IFF_ALLMULTI >>> + is important. Some (broken) drivers set IFF_PROMISC, when >>> + IFF_ALLMULTI is requested not asking us and not reporting. >>> + */ >>> if (dev->flags & IFF_PROMISC) >>> dev_set_promiscuity(real_dev, 1); >>> + if (dev->flags & IFF_ALLMULTI) >>> + dev_set_allmulti(real_dev, 1); >> >> What exactly is the problem here? The VLAN code is obviously not >> one of the broken drivers, so why should it care what other drivers >> do? >> > > I think the problem is that allmulti is not valid if promis is not on. No, PROMISC is a superset of ALLMULTI. > And about the comment, I copy it from dev_change_flags() and think > it seems suit for here. > Did I misunderstand this comment? I think it refers to broken behaviour by drivers that set IFF_PROMISC themselves when asked to disable multicast filtering by setting IFF_ALLMULTI. This would cause the test for changed flags in dev_set_promiscuity to return zero and not program the device for promiscous mode properly. There are a few examples of this in the tree. But calling dev_set_promiscuity() before dev_set_allmulti() only helps in the dev_change_flags() case since its the only function that might change both flags at once. In all other cases it depends on the caller. So for the dev_change_flags() case VLAN already uses the "proper" ordering, the other cases might be broken with or without your patch. I'd suggest to fix the drivers instead, perhaps start by adding a warning to dev_change_flags() that is triggered by the driver changing the flags itself.