Re: [PATCH net-next 1/4] vxlan: Join / leave MC group after remote changes

[Petr Machata <petrm@nvidia.com>]

Paolo Abeni <pabeni@redhat.com> writes:

> On 2/7/25 6:34 PM, Petr Machata wrote:
>> @@ -3899,6 +3904,11 @@ static void vxlan_config_apply(struct net_device *dev,
>>  			dev->mtu = conf->mtu;
>>  
>>  		vxlan->net = src_net;
>> +
>> +	} else if (vxlan->dev->flags & IFF_UP) {
>> +		if (vxlan_addr_multicast(&vxlan->default_dst.remote_ip) &&
>> +		    rem_changed)
>> +			vxlan_multicast_leave(vxlan);
>
> AFAICS vxlan_vni_update_group() is not completely ignore
> vxlan_multicast_{leave,join} errors. Instead is bailing out as soon as
> any error happens. For consistency's sake I think it would be better do
> the same here.
>
> Also I have the feeling that ending-up in an inconsistent status with no
> group joined would be less troublesome than the opposite.

This can already happen FWIW. If you currently want to change the remote
group address in a way that doesn't break things, you take the netdevice
down, then change it, then bring it back up. The leave during downing
can fail and will not be diagnosed. (Nor can it really be, you can't
veto downing.)

I can add the bail-outs that you ask for, but I don't know that there is
a way to resolve these issues for real.