netdev - Re: [PATCH net] ip6_tunnel: fix GRE6 segmentation

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Date:   Wed, 23 Jun 2021 12:28:05 -0600
From:   David Ahern <dsahern@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, vfedorenko@...ek.ru
Subject: Re: [PATCH net] ip6_tunnel: fix GRE6 segmentation

On 6/23/21 10:14 AM, Jakub Kicinski wrote:
> On Tue, 22 Jun 2021 21:47:45 -0600 David Ahern wrote:
>> On 6/22/21 4:24 PM, Jakub Kicinski wrote:
>>>> would be good to capture the GRE use case that found the bug and the
>>>> MPLS version as test cases under tools/testing/selftests/net. Both
>>>> should be doable using namespaces.  
>>>
>>> I believe Vadim is working on MPLS side, how does this look for GRE?
>>
>> I like the template you followed. :-)
> 
> :)
> 
>> The test case looks good to me, thanks for doing it.
> 
> Noob question, why do we need that 2 sec wait with IPv6 sometimes?
> I've seen it randomly in my local testing as well I wasn't sure if 
> it's a bug or expected.

It is to let IPv6 DAD to complete otherwise the address will not be
selected as a source address. That typically results in test failures.
There are sysctl settings that can prevent the race and hence the need
for the sleep.

> 
> I make a v6 tunnel on top of a VLAN and for 2 secs after creation 
> I get the wrong route in ip -6 r g.
>