netdev - Re: [RFC PATCH net 3/4] ipv6: datagram: Update dst cache of a connected datagram sk during pmtu update

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Message-ID: <20160411175557.GA68004@kafai-mba.local>
Date:	Mon, 11 Apr 2016 10:56:29 -0700
From:	Martin KaFai Lau <kafai@...com>
To:	David Miller <davem@...emloft.net>, <xiyou.wangcong@...il.com>
CC:	<netdev@...r.kernel.org>, <edumazet@...gle.com>,
	<weiwan@...gle.com>, <kernel-team@...com>
Subject: Re: [RFC PATCH net 3/4] ipv6: datagram: Update dst cache of a
 connected datagram sk during pmtu update

On Tue, Apr 05, 2016 at 07:56:54PM -0400, David Miller wrote:
> From: Cong Wang <xiyou.wangcong@...il.com>
> Date: Mon, 4 Apr 2016 13:45:02 -0700
>
> > On Sat, Apr 2, 2016 at 7:33 PM, Martin KaFai Lau <kafai@...com> wrote:
> >> One thing to note is that this patch uses the addresses from the sk
> >> instead of iph when updating sk->sk_dst_cache.  It is basically the
> >> same logic that the __ip6_datagram_connect() is doing, so some
> >> refactoring works in the first two patches.
> >>
> >> AFAIK, a UDP socket can become connected after sending out some
> >> datagrams in un-connected state.  or It can be connected
> >> multiple times to different destinations.  I did some quick
> >> tests but I could be wrong.
> >>
> >> I am thinking if there could be a chance that the skb->data, which
> >> has the original outgoing iph, is not related to the current
> >> connected address.  If it is possible, we have to specifically
> >> use the addresses in the sk instead of skb->data (i.e. iph) when
> >> updating the sk->sk_dst_cache.
> >>
> >> If we need to use the sk addresses (and other info) to find out a
> >> new dst for a connected udp socket, it is better not doing it while
> >> the userland is connecting to somewhere else.
> >>
> >> If the above case is impossible, we can keep using the info from iph to
> >> do the dst update for a connected-udp sk without taking the lock.
> >
> > I see your point, but calling __ip6_datagram_connect() seems overkill
> > here, we don't need to update so many things in the pmtu update context,
> > at least IPv4 doesn't do that either. I don't think you have to do that.
> >
> > So why just updating the dst cache (also some addr cache) here is not
> > enough?
>
> I think we are steadily getting closer to a version of this fix that
> we have some agreement on, right?
>
> Martin can you address Cong's feedback and spin another version of this
> series?
Dave, I will spin v2 shortly with some minor changes.

Cong, I believe the loose ends have been tied up after the last email thread
since last Thursday?