From mboxrd@z Thu Jan 1 00:00:00 1970 From: Duan Jiong Subject: Re: [PATCH v2] neigh: set nud_state to NUD_INCOMPLETE when probing router reachability Date: Tue, 13 May 2014 13:12:29 +0800 Message-ID: <5371A9BD.2020106@cn.fujitsu.com> References: <53703F52.9060900@cn.fujitsu.com> <20140512.143720.896863177762079657.davem@davemloft.net> <53717040.2070102@cn.fujitsu.com> <20140512.232511.1061979369646724590.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-2022-JP" Content-Transfer-Encoding: 7bit Cc: , , To: David Miller Return-path: Received: from cn.fujitsu.com ([59.151.112.132]:23974 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1758289AbaEMFOw (ORCPT ); Tue, 13 May 2014 01:14:52 -0400 In-Reply-To: <20140512.232511.1061979369646724590.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: 于 2014年05月13日 11:25, David Miller 写道: > From: Duan Jiong > Date: Tue, 13 May 2014 09:07:12 +0800 > >> 于 2014年05月13日 02:37, David Miller 写道: >>> From: Duan Jiong >>> Date: Mon, 12 May 2014 11:26:10 +0800 >>> >>>> 于 2014年05月12日 06:04, Hannes Frederic Sowa 写道: >>>>> On Thu, May 8, 2014, at 22:16, Duan Jiong wrote: >>>>>> >>>>>> Since commit 7e98056964("ipv6: router reachability probing"), a router falls >>>>>> into NUD_FAILED will be probed. >>>>>> >>>>>> Now if function rt6_select() selects a router which neighbour state is NUD_FAILED, >>>>>> and at the same time function rt6_probe() changes the neighbour state to NUD_PROBE, >>>>>> then function dst_neigh_output() can directly send packets, but actually the >>>>>> neighbour still is unreachable. If we set nud_state to NUD_INCOMPLETE instead >>>>>> NUD_PROBE, packets will not be sent out until the neihbour is reachable. >>>>>> >>>>>> In addition, because the route should be probes with a single NS, so we must >>>>>> set neigh->probes to neigh_max_probes(), then the neigh timer timeout and function >>>>>> neigh_timer_handler() will not send other NS Messages. >>>>>> >>>>>> Signed-off-by: Duan Jiong >>>>>> --- >>>>>> Changes from v1: >>>>>> *modify changelog to explain in detail why use neigh_max_probes(). >>>>>> >>>>>> net/core/neighbour.c | 4 ++-- >>>>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/net/core/neighbour.c b/net/core/neighbour.c >>>>>> index 8f8a96e..32d872e 100644 >>>>>> --- a/net/core/neighbour.c >>>>>> +++ b/net/core/neighbour.c >>>>>> @@ -1248,8 +1248,8 @@ void __neigh_set_probe_once(struct neighbour *neigh) >>>>>> neigh->updated = jiffies; >>>>>> if (!(neigh->nud_state & NUD_FAILED)) >>>>>> return; >>>>>> - neigh->nud_state = NUD_PROBE; >>>>>> - atomic_set(&neigh->probes, NEIGH_VAR(neigh->parms, UCAST_PROBES)); >>>>>> + neigh->nud_state = NUD_INCOMPLETE; >>>>>> + atomic_set(&neigh->probes, neigh_max_probes(neigh)); >>>>> >>>>> Wouldn't it be better if we neigh_suspect the neighbour and leaving the state in NUD_PROBE? We call down to ->output in case neighbour is in NUD_PROBE state, so we must just disable connected 'fast-path'. >>>>> >>>> >>>> You can look into neigh_event_send() called in neigh_resolve_output(), and if neigh->nud_state >>>> still is NUD_PROBE, the neigh_event_send() will return 0, so the packet will still be sent out >>>> without probe. >>>> >>>> So, using neigh_suspect is not a good idea. >>> >>> If you set it to NUD_INCOMPLETE however, neigh_event_send() is going to add the packet >>> to the neigh's ARP queue and return '1'. >>> >>> Is that really what you want to happen in this case? >> >> Yes, packets should not be sent out until the neihbour is reachable. > > But shouldn't we be using the router in the list which did not enter > NUD_FAILED in this situation? > . In situation of connected router, the router which enter NUD_FAILED will never be choosed, and we only probe NUD_FAILED router's reachability by sending a single Neighbor Solicitation to that router's address. Finally， we still send packets out through the connected router.