Re: [PATCH] mpls: Do not decrement alive counter for unregister events

[David Miller <davem@davemloft.net>]

From: David Ahern <dsa@cumulusnetworks.com>
Date: Fri, 10 Mar 2017 14:11:39 -0800

> Multipath routes can be rendered usesless when a device in one of the
> paths is deleted. For example:
> 
> $ ip -f mpls ro ls
> 100
> 	nexthop as to 200 via inet 172.16.2.2  dev virt12
> 	nexthop as to 300 via inet 172.16.3.2  dev br0
> 101
> 	nexthop as to 201 via inet6 2000:2::2  dev virt12
> 	nexthop as to 301 via inet6 2000:3::2  dev br0
> 
> $ ip li del br0
> 
> When br0 is deleted the other hop is not considered in
> mpls_select_multipath because of the alive check -- rt_nhn_alive
> is 0.
> 
> rt_nhn_alive is decremented once in mpls_ifdown when the device is taken
> down (NETDEV_DOWN) and again when it is deleted (NETDEV_UNREGISTER). For
> a 2 hop route, deleting one device drops the alive count to 0. Since
> devices are taken down before unregistering, the decrement on
> NETDEV_UNREGISTER is redundant.
> 
> Fixes: c89359a42e2a4 ("mpls: support for dead routes")
> Signed-off-by: David Ahern <dsa@cumulusnetworks.com>

Applied and queued up for -stable, thanks David.