[LTP] [RFC] [PATCH] netns: Fix race in virtual interface bringup

[Dan Rue]

On Thu, Nov 16, 2017 at 3:56 AM, Nicolas Dichtel
<nicolas.dichtel@6wind.com> wrote:
> Le 15/11/2017 à 20:04, Dan Rue a écrit :
>> Adding CC netdev
>>
>> Can someone comment on the expected behavior of this test case?
>>
>> Here's the isolated test:
>>
>>     ip netns del tst_net_ns0
>>     ip netns del tst_net_ns1
>>     ip netns add tst_net_ns0
>>     ip netns add tst_net_ns1
>>     ip netns exec tst_net_ns0 ip link add veth0 type veth peer name veth1
>>     ip netns exec tst_net_ns0 ip link set veth1 netns tst_net_ns1
>>
>>     ip netns exec tst_net_ns0 ifconfig veth0 inet6 add fd00::2/64
>>     ip netns exec tst_net_ns1 ifconfig veth1 inet6 add fd00::3/64
> ip netns exec tst_net_ns0 sysctl -w net.ipv6.conf.all.accept_dad=0
> ip netns exec tst_net_ns0 sysctl -w net.ipv6.conf.veth0.accept_dad=0
> ip netns exec tst_net_ns1 sysctl -w net.ipv6.conf.all.accept_dad=0
> ip netns exec tst_net_ns1 sysctl -w net.ipv6.conf.veth1.accept_dad=0
>
>>     ip netns exec tst_net_ns0 ifconfig veth0 up
>>     ip netns exec tst_net_ns1 ifconfig veth1 up
>>
>>     #sleep 2>
>>     ip netns exec tst_net_ns0 ping6 -q -c2 -I veth0 fd00::3
>>
>> This is essentially what LTP is running. Sometimes, on some systems,
>> ping6 fails with "connect: Cannot assign requested address". Adding a
>> "sleep 2" always fixes it (but we'd obviously like to avoid a hard coded
>> sleep in the test).
> Probably due to DAD. By disabling DAD, you should be able to use immediately the
> ipv6 addrs.

Oh, that does work! I was trying to disable dad using
'echo 0 > /proc/sys/net/ipv6/conf/veth0/accept_dad' and I guess it was
not sufficient.
Using your example, it did work.

Thanks! I will submit this patch.

Dan