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Subject[PATCH 4.10 41/63] mpls: Do not decrement alive counter for unregister events
Date
4.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Ahern <dsa@cumulusnetworks.com>


[ Upstream commit 79099aab38c8f5c746748b066ae74ba984fe2cc8 ]

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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/mpls/af_mpls.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -956,7 +956,8 @@ static void mpls_ifdown(struct net_devic
/* 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)

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