From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wang Chen Subject: Re: [PATCH 3/3] netdevice: order of synchronization of IFF_PROMISC and IFF_ALLMULTI Date: Tue, 17 Jun 2008 09:42:57 +0800 Message-ID: <485716A1.8030401@cn.fujitsu.com> References: <48562F9A.5030509@cn.fujitsu.com> <485631FF.7040509@trash.net> <485634D1.2010603@cn.fujitsu.com> <48563A7F.50309@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , NETDEV To: Patrick McHardy Return-path: Received: from cn.fujitsu.com ([222.73.24.84]:51783 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752011AbYFQBqp (ORCPT ); Mon, 16 Jun 2008 21:46:45 -0400 In-Reply-To: <48563A7F.50309@trash.net> Sender: netdev-owner@vger.kernel.org List-ID: Patrick McHardy said the following on 2008-6-16 18:03: > 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. > Do you mean things like that in do_mc32_set_multicast_list()? > 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. > Is there any other case might be broken? > 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. > In some driver's code of *_set_multicast_list(), IFF_PROMISC will be set if IFF_ALLMULTI is set. And there is comment about the necessity for setting IFF_PROMISC. /* * We must make the kernel realise we had to move * into promisc mode or we start all out war on * the cable. If it was a promisc request the * flag is already set. If not we assert it. */ So, I doubt about fixing the drivers.