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mpls: Do not decrement alive counter for unregister events 

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: c89359a42e ("mpls: support for dead routes")
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Ahern 2017-03-10 14:11:39 -08:00 committed by David S. Miller
parent b17075d5c1
commit 79099aab38
1 changed files with 2 additions and 1 deletions
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3
net/mpls/af_mpls.c
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@ -1288,7 +1288,8 @@ static void mpls_ifdown(struct net_device *dev, int event)
/* fall through */
case NETDEV_CHANGE:
nh->nh_flags |= RTNH_F_LINKDOWN;
ACCESS_ONCE(rt->rt_nhn_alive) = rt->rt_nhn_alive - 1;
if (event != NETDEV_UNREGISTER)
ACCESS_ONCE(rt->rt_nhn_alive) = rt->rt_nhn_alive - 1;
break;
}
if (event == NETDEV_UNREGISTER)