Re: [PATCHv2 net 2/2] ipv4: update RTNH_F_LINKDOWN flag on UP event
From: Andy Gospodarek <hidden>
Date: 2015-10-27 04:52:08
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
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.
quoted hunk ↗ jump to hunk
Fixes: 8a3d03166f19 ("net: track link-status of ipv4 nexthops") Signed-off-by: Julian Anastasov <ja@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++;