On Mon, Oct 26, 2015 at 11:59:13PM +0200, Julian Anastasov wrote:
> When nexthop is part of multipath route we should clear the
> LINKDOWN flag when link goes UP or when first address is added.
> This is needed because we always set LINKDOWN flag when DEAD flag
> was set but now on UP the nexthop is not dead anymore. Examples when
> LINKDOWN bit can be forgotten when no NETDEV_CHANGE is delivered:
>
> - link goes down (LINKDOWN is set), then link goes UP and device
> shows carrier OK but LINKDOWN remains set
>
> - last address is deleted (LINKDOWN is set), then address is
> added and device shows carrier OK but LINKDOWN remains set
>
> Steps to reproduce:
> modprobe dummy
> ifconfig dummy0 192.168.168.1 up
>
> here add a multipath route where one nexthop is for dummy0:
>
> ip route add 1.2.3.4 nexthop dummy0 nexthop SOME_OTHER_DEVICE
> ifconfig dummy0 down
> ifconfig dummy0 up
>
> now ip route shows nexthop that is not dead. Now set the sysctl var:
>
> echo 1 > /proc/sys/net/ipv4/conf/dummy0/ignore_routes_with_linkdown
>
> now ip route will show a dead nexthop because the forgotten
> RTNH_F_LINKDOWN is propagated as RTNH_F_DEAD.
I tested this patch and I now see that your reported problem is a result
of dummy never taking carrier down. There was a presumption that
carrier notification would go down when hardware went down (or when the
logical device backing the hardware went down, but this is clearly not
always the case.
> Fixes: 8a3d03166f19 ("net: track link-status of ipv4 nexthops")
> Signed-off-by: Julian Anastasov <j...@ssi.bg>
> ---
> net/ipv4/fib_semantics.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
> index f493eff..f657418 100644
> --- a/net/ipv4/fib_semantics.c
> +++ b/net/ipv4/fib_semantics.c
> @@ -1445,6 +1445,13 @@ int fib_sync_up(struct net_device *dev, unsigned int
> nh_flags)
> if (!(dev->flags & IFF_UP))
> return 0;
>
> + if (nh_flags & RTNH_F_DEAD) {
> + unsigned int flags = dev_get_flags(dev);
> +
> + if (flags & (IFF_RUNNING | IFF_LOWER_UP))
> + nh_flags |= RTNH_F_LINKDOWN;
> + }
> +
> prev_fi = NULL;
> hash = fib_devindex_hashfn(dev->ifindex);
> head = &fib_info_devhash[hash];
Logically this patch makes sense, but I feel as though there may be a
slightly better option. Possibly this:
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 42778d9..7eb7c40 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1376,7 +1376,8 @@ int fib_sync_down_dev(struct net_device *dev, unsigned
long event)
nexthop_nh->nh_flags |= RTNH_F_DEAD;
/* fall through */
case NETDEV_CHANGE:
- nexthop_nh->nh_flags |= RTNH_F_LINKDOWN;
+ if (!netif_carrier_ok(dev))
+ nexthop_nh->nh_flags |=
RTNH_F_LINKDOWN;
break;
}
dead++;
@@ -1396,7 +1397,8 @@ int fib_sync_down_dev(struct net_device *dev, unsigned
long event)
fi->fib_flags |= RTNH_F_DEAD;
/* fall through */
case NETDEV_CHANGE:
- fi->fib_flags |= RTNH_F_LINKDOWN;
+ if (!netif_carrier_ok(dev))
+ fi->fib_flags |= RTNH_F_LINKDOWN;
break;
}
ret++;
--
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