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Date:   Thu, 19 Mar 2020 15:41:08 -0700
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Jarod Wilson <jarod@redhat.com>
Cc:     Eric Dumazet <eric.dumazet@gmail.com>,
        Jay Vosburgh <jay.vosburgh@canonical.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Moshe Levi <moshele@mellanox.com>,
        Marcelo Ricardo Leitner <mleitner@redhat.com>,
        Netdev <netdev@vger.kernel.org>
Subject: Re: [PATCH net] ipv6: don't auto-add link-local address to lag
 ports
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On Thu, 19 Mar 2020 15:29:51 -0400
Jarod Wilson <jarod@redhat.com> wrote:

> On Thu, Mar 19, 2020 at 1:06 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >
> > On 3/19/20 9:42 AM, Jarod Wilson wrote:
> >  
> > > Interesting. We'll keep digging over here, but that's definitely not
> > > working for this particular use case with OVS for whatever reason.  
> >
> > I did a quick test and confirmed that my bonding slaves do not have link-local addresses,
> > without anything done to prevent them to appear.
> >
> > You might add a selftest, if you ever find what is the trigger :)  
> 
> Okay, have a basic reproducer, courtesy of Marcelo:
> 
> # ip link add name bond0 type bond
> # ip link set dev ens2f0np0 master bond0
> # ip link set dev ens2f1np2 master bond0
> # ip link set dev bond0 up
> # ip a s
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
> group default qlen 1000
>     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>     inet 127.0.0.1/8 scope host lo
>        valid_lft forever preferred_lft forever
>     inet6 ::1/128 scope host
>        valid_lft forever preferred_lft forever
> 2: ens2f0np0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc
> mq master bond0 state UP group default qlen 1000
>     link/ether 00:0f:53:2f:ea:40 brd ff:ff:ff:ff:ff:ff
> 5: ens2f1np2: <NO-CARRIER,BROADCAST,MULTICAST,SLAVE,UP> mtu 1500 qdisc
> mq master bond0 state DOWN group default qlen 1000
>     link/ether 00:0f:53:2f:ea:40 brd ff:ff:ff:ff:ff:ff
> 11: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc
> noqueue state UP group default qlen 1000
>     link/ether 00:0f:53:2f:ea:40 brd ff:ff:ff:ff:ff:ff
>     inet6 fe80::20f:53ff:fe2f:ea40/64 scope link
>        valid_lft forever preferred_lft forever
> 
> (above trimmed to relevant entries, obviously)
> 
> # sysctl net.ipv6.conf.ens2f0np0.addr_gen_mode=0
> net.ipv6.conf.ens2f0np0.addr_gen_mode = 0
> # sysctl net.ipv6.conf.ens2f1np2.addr_gen_mode=0
> net.ipv6.conf.ens2f1np2.addr_gen_mode = 0
> 
> # ip a l ens2f0np0
> 2: ens2f0np0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc
> mq master bond0 state UP group default qlen 1000
>     link/ether 00:0f:53:2f:ea:40 brd ff:ff:ff:ff:ff:ff
>     inet6 fe80::20f:53ff:fe2f:ea40/64 scope link tentative
>        valid_lft forever preferred_lft forever
> # ip a l ens2f1np2
> 5: ens2f1np2: <NO-CARRIER,BROADCAST,MULTICAST,SLAVE,UP> mtu 1500 qdisc
> mq master bond0 state DOWN group default qlen 1000
>     link/ether 00:0f:53:2f:ea:40 brd ff:ff:ff:ff:ff:ff
>     inet6 fe80::20f:53ff:fe2f:ea40/64 scope link tentative
>        valid_lft forever preferred_lft forever
> 
> Looks like addrconf_sysctl_addr_gen_mode() bypasses the original "is
> this a slave interface?" check, and results in an address getting
> added, while w/the proposed patch added, no address gets added.
> 
> Looking back through git history again, I see a bunch of 'Fixes:
> d35a00b8e33d ("net/ipv6: allow sysctl to change link-local address
> generation mode")' patches, and I guess that's where this issue was
> also introduced.
> 

Yes the addrgen mode patches caused bad things to happen with hyper-v
sub devices.  Addrconf code is very tricky to get right.
If you look back there have been a large number of changes where
a patch looks good, gets reviewed, merged, and then breaks something
and has to be reverted.

Probably the original patch should just be reverted rather than
trying to add more here.