From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Benc Subject: Re: [PATCH net] net: try harder to not reuse ifindex when moving interfaces Date: Thu, 22 Oct 2015 17:00:59 +0200 Message-ID: <20151022170100.1e45a8b8@griffin> References: <20151021164613.24650836@griffin> <20151021.083214.534622235927401863.davem@davemloft.net> <20151021172502.63220dbb@griffin> <20151021.085635.1582760365341524949.davem@davemloft.net> <1445447578.1265325.416533273.3D5599FD@webmail.messagingengine.com> <5628F81D.1070009@6wind.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Hannes Frederic Sowa , David Miller , netdev@vger.kernel.org, thaller@redhat.com To: Nicolas Dichtel Return-path: Received: from mx1.redhat.com ([209.132.183.28]:46808 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750989AbbJVPBE (ORCPT ); Thu, 22 Oct 2015 11:01:04 -0400 In-Reply-To: <5628F81D.1070009@6wind.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 22 Oct 2015 16:52:13 +0200, Nicolas Dichtel wrote: > With the proposed scenario: > 1. create netns 'new_netns' > 2. in root netns, move the interface with ifindex 2 to new_netns > 3. in new_netns, delete the interface with ifindex 2 > 4. in new_netns, create an interface - it will get ifindex 2 > > Operation 2 and 4 are done by dev_change_net_namespace() under rtnl_lock(). > RTM_DELLINK(root netns) and RTM_NEWLINK(new_netns) are sent by this function. > It means that operation 3 has been done before and that RTM_DELLINK(new_netns) > has been sent before. Imagine the application trying to configure the interface with ifindex 2 after your step 2. It constructs a netlink message and sends it to the kernel; but while doing so, steps 3 and 4 happen. Now the application ends up configuring a different interface than it intended to. After that, it polls the netlink socket and receives the notifications about interface disappearing and a new one appearing. I don't see any way the user space application can prevent this. There will always be a race between receiving netlink notifications and sending config requests. I guess Thomas Haller can elaborate more as he ran into this. Jiri -- Jiri Benc