From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933816AbXCSFS4 (ORCPT ); Mon, 19 Mar 2007 01:18:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965047AbXCSFS4 (ORCPT ); Mon, 19 Mar 2007 01:18:56 -0400 Received: from ug-out-1314.google.com ([66.249.92.175]:39017 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933827AbXCSFSz (ORCPT ); Mon, 19 Mar 2007 01:18:55 -0400 Date: Mon, 19 Mar 2007 07:19:34 +0200 From: "Michael S. Tsirkin" To: David Miller Cc: mst@dev.mellanox.co.il, ebiederman@lnxi.com, kuznet@ms2.inr.ac.ru, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, general@lists.openfabrics.org Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband? Message-ID: <20070319051934.GS11078@mellanox.co.il> Reply-To: "Michael S. Tsirkin" References: <20070318223653.GO11078@mellanox.co.il> <20070318224234.GP11078@mellanox.co.il> <20070318.171337.112622504.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070318.171337.112622504.davem@davemloft.net> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > Quoting David Miller : > Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband? > > From: "Michael S. Tsirkin" > Date: Mon, 19 Mar 2007 00:42:34 +0200 > > > > Quoting Michael S. Tsirkin : > > > Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband? > > > > > > > Quoting Eric W. Biederman : > > > > Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband? > > > > > > > > "Michael S. Tsirkin" writes: > > > > > > > > >> > Why is neighbour->dev changed here? > > > > >> > > > > >> It holds reference to device and prevents its destruction. > > > > >> If dst is held somewhere, we cannot destroy the device and deadlock > > > > >> while unregister. > > > > > > > > > > BTW, can this ever happen for the loopback device itself? > > > > > Is it ever unregistered? > > > > > > > > Well I don't think the loopback device is currently but as soon > > > > as we get network namespace support we will have multiple loopback > > > > devices and they will get unregistered when we remove the network > > > > namespace. > > > > > > Hmm. Then the code moving dst->dev to point to the loopback > > > device will have to be fixed too. I'll post a patch a bit later. > > > > Does this look sane (untested)? > > > > Signed-off-by: Michael S. Tsirkin > > You can't point it at NULL, we don't point it at loopback > just for fun. > > There can be asynchronous paths elsewhere in the networking still > referencing the neigh or dst and they will (correctly) feel free to > derefence whatever device is hanging there. So transitioning > to NULL is invalid. > > You guys will need to come up with a better solution for this silly > situation with network namespaces. Loopback is always available to > point dead routes and neighbour entries at, and this assumption is > massively rooted in the networking. Yes, I see this now. I guess it's best to focus on the original problem with dst_ifdown breaking infiniband for now. For that, we have to audit all the places where dst->neighbour is dereferenced for RCU safety, and this is already a massive task. -- MST