From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Rosenboom Subject: Re: [RFC] net/core: Delay neighbor only if it has been used after confirmed Date: Wed, 02 Sep 2009 15:03:29 +0200 Message-ID: <1251896609.5813.32.camel@fnki-nb00130> References: <1251883079.5813.18.camel@fnki-nb00130> <4A9E639B.20907@linux-ipv6.org> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Linux Network Developers To: YOSHIFUJI Hideaki Return-path: Received: from leia.mcbone.net ([194.97.104.42]:42533 "EHLO leia.mcbone.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751081AbZIBNDg (ORCPT ); Wed, 2 Sep 2009 09:03:36 -0400 In-Reply-To: <4A9E639B.20907@linux-ipv6.org> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2009-09-02 at 21:22 +0900, YOSHIFUJI Hideaki wrote: > Hello. > > Jens Rosenboom wrote: > > When doing some IPv6 testing with the router advertising a small (e.g. 5 > > seconds) reachable time, I noticed that after the traffic has stopped, > > hosts continue to exchange ND packets every 10 seconds. This is due to > > neigh_timer_handler() only checking neigh->used and puts a neighbor into > > NUD_DELAY state even if neigh->confirmed may be >= neigh->used. > > Well, as you can see in neigh_periodic_timer(): > | if (time_before(n->used, n->confirmed)) > | n->used = n->confirmed; > time_after_eq(n->used, n->confirmed) should be taken valid; > confirmed <= used <= now <= jiffies Isn't there a chance that neigh_timer_handler() is run before the periodic timer fixes this? Otherwise I agree that the test could just say (n->used != n->confirmed). > > The following patch for net-next-2.6 fixes this behaviour for my IPv6 > > setup, however I would like to hear some opinion on whether this might > > have some negative influence on other protocols that use this code. > > > > I also think that it would make more sense to compute the time for the > > delay timer starting from neigh->used instead of using now (second part > > of the patch). > > okay, but I would rather have this in another patch. > > > diff --git a/net/core/neighbour.c b/net/core/neighbour.c > > index 5bc4ad5..ca20162 100644 > > --- a/net/core/neighbour.c > > +++ b/net/core/neighbour.c > > @@ -820,12 +820,13 @@ static void neigh_timer_handler(unsigned long arg) > > NEIGH_PRINTK2("neigh %p is still alive.\n", neigh); > > next = neigh->confirmed + neigh->parms->reachable_time; > > } else if (time_before_eq(now, > > - neigh->used + neigh->parms->delay_probe_time)) { > > + neigh->used + neigh->parms->delay_probe_time) && > > + time_after(neigh->confirmed, neigh->used)) { > > NEIGH_PRINTK2("neigh %p is delayed.\n", neigh); > > neigh->nud_state = NUD_DELAY; > > I think your change should be > | time_after(neigh->used, neigh->confirmed) > or > | time_before(neigh->confirmed, neigh->used) > > ("_eq" is removed because there is a little chance > that the neighbor had been confirmed just before it was > used. It is not interesting for us at this moment.) > > No? Yes, you are right, this test should be reversed. But together with your remarks above, this probably means that the whole stuff also works fine if we completely remove this if-branch. > And, this "if" for REACHABLE->DELAY may be completely needless. > Timer in REACHABLE is only for state transition for toward REACHABLE > or STALE. Well, this part has been there for a long time, at least it looks pretty much the same in the first git version, so I would be a bit reluctant to completely remove it, but since that would probably also solve my problem, I also wouldn't object that proposition. ;-)