netdev - Re: [PATCHv2 net] ipv6/route: should not update neigh confirm time during PMTU update

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Message-ID: <20191203102534.GK18865@dhcp-12-139.nay.redhat.com>
Date:   Tue, 3 Dec 2019 18:25:35 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, ja@....bg, marcelo.leitner@...il.com,
        dsahern@...il.com, edumazet@...gle.com
Subject: Re: [PATCHv2 net] ipv6/route: should not update neigh confirm time
 during PMTU update


Hi David,
On Tue, Dec 03, 2019 at 06:15:36PM +0800, Hangbin Liu wrote:
> On Mon, Dec 02, 2019 at 06:47:04PM -0800, David Miller wrote:
> > From: Hangbin Liu <liuhangbin@...il.com>
> > Date: Tue,  3 Dec 2019 10:11:37 +0800
> > 
> > > Fix it by removing the dst_confirm_neigh() in __ip6_rt_update_pmtu() as
> > > there is no two-way communication during PMTU update.
> > > 
> > > v2: remove dst_confirm_neigh directly as David Miller pointed out.
> > 
> > That's not what I said.
> > 
> > I said that this interface is designed for situations where the neigh
> > update is appropriate, and that's what happens for most callers _except_
> > these tunnel cases.
> > 
> > The tunnel use is the exception and invoking the interface
> > inappropriately.
> > 
> > It is important to keep the neigh reachability fresh for TCP flows so
> > you cannot remove this dst_confirm_neigh() call.

I have one question here. Since we have the .confirm_neigh fuction in
struct dst_ops. How about do a dst->ops->confirm_neigh() separately after
dst->ops->update_pmtu()? Why should we mix the confirm_neigh() in
update_pmtu(), like ip6_rt_update_pmtu()?

Thanks
Hangbin