From: David Ahern Date: Thu, 7 Apr 2016 14:21:00 +0000 (-0700) Subject: net: ipv4: Consider failed nexthops in multipath routes X-Git-Tag: v4.1.12-124.31.3~796 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=0fbdc0df27ab2fc6828279be8954af45793ea9d9;p=users%2Fjedix%2Flinux-maple.git net: ipv4: Consider failed nexthops in multipath routes Multipath route lookups should consider knowledge about next hops and not select a hop that is known to be failed. Example: [h2] [h3] 15.0.0.5 | | 3| 3| [SP1] [SP2]--+ 1 2 1 2 | | /-------------+ | | \ / | | X | | / \ | | / \---------------\ | 1 2 1 2 12.0.0.2 [TOR1] 3-----------------3 [TOR2] 12.0.0.3 4 4 \ / \ / \ / -------| |-----/ 1 2 [TOR3] 3| | [h1] 12.0.0.1 host h1 with IP 12.0.0.1 has 2 paths to host h3 at 15.0.0.5: root@h1:~# ip ro ls ... 12.0.0.0/24 dev swp1 proto kernel scope link src 12.0.0.1 15.0.0.0/16 nexthop via 12.0.0.2 dev swp1 weight 1 nexthop via 12.0.0.3 dev swp1 weight 1 ... If the link between tor3 and tor1 is down and the link between tor1 and tor2 then tor1 is effectively cut-off from h1. Yet the route lookups in h1 are alternating between the 2 routes: ping 15.0.0.5 gets one and ssh 15.0.0.5 gets the other. Connections that attempt to use the 12.0.0.2 nexthop fail since that neighbor is not reachable: root@h1:~# ip neigh show ... 12.0.0.3 dev swp1 lladdr 00:02:00:00:00:1b REACHABLE 12.0.0.2 dev swp1 FAILED ... The failed path can be avoided by considering known neighbor information when selecting next hops. If the neighbor lookup fails we have no knowledge about the nexthop, so give it a shot. If there is an entry then only select the nexthop if the state is sane. This is similar to what fib_detect_death does. To maintain backward compatibility use of the neighbor information is based on a new sysctl, fib_multipath_use_neigh. Orabug: 27547114 Signed-off-by: David Ahern Reviewed-by: Julian Anastasov Signed-off-by: David S. Miller (cherry picked from commit a6db4494d218c2e559173661ee972e048dc04fdd) Reviewed-by: Zhu Yanjun Signed-off-by: Venkat Venkatsubra Signed-off-by: Brian Maly Conflicts: net/ipv4/fib_semantics.c net/ipv4/sysctl_net_ipv4.c Signed-off-by: Brian Maly --- diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index 43227b2bb2e65..8686ccd8563fd 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -63,6 +63,16 @@ fwmark_reflect - BOOLEAN fwmark of the packet they are replying to. Default: 0 +fib_multipath_use_neigh - BOOLEAN + Use status of existing neighbor entry when determining nexthop for + multipath routes. If disabled, neighbor information is not used and + packets could be directed to a failed nexthop. Only valid for kernels + built with CONFIG_IP_ROUTE_MULTIPATH enabled. + Default: 0 (disabled) + Possible values: + 0 - disabled + 1 - enabled + route/max_size - INTEGER Maximum number of routes allowed in the kernel. Increase this when using large numbers of interfaces and/or routes. diff --git a/include/net/route.h b/include/net/route.h index fe22d03afb6a2..90a956bde3eee 100644 --- a/include/net/route.h +++ b/include/net/route.h @@ -44,6 +44,10 @@ #define RT_CONN_FLAGS(sk) (RT_TOS(inet_sk(sk)->tos) | sock_flag(sk, SOCK_LOCALROUTE)) #define RT_CONN_FLAGS_TOS(sk,tos) (RT_TOS(tos) | sock_flag(sk, SOCK_LOCALROUTE)) +#ifdef CONFIG_IP_ROUTE_MULTIPATH +extern int sysctl_fib_multipath_use_neigh; +#endif + struct fib_nh; struct fib_info; struct uncached_list; diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index a867a4f829a91..b3b10a64b0df0 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -1316,19 +1316,43 @@ int fib_sync_up(struct net_device *dev) return ret; } +static bool fib_good_nh(const struct fib_nh *nh) +{ + int state = NUD_REACHABLE; + + if (nh->nh_scope == RT_SCOPE_LINK) { + struct neighbour *n; + + rcu_read_lock_bh(); + + n = __ipv4_neigh_lookup_noref(nh->nh_dev, nh->nh_gw); + if (n) + state = n->nud_state; + + rcu_read_unlock_bh(); + } + + return !!(state & NUD_VALID); +} + void fib_select_multipath(struct fib_result *res, int hash) { struct fib_info *fi = res->fi; + bool first = false; for_nexthops(fi) { if (hash > atomic_read(&nh->nh_upper_bound)) continue; - res->nh_sel = nhsel; - return; + if (!sysctl_fib_multipath_use_neigh || + fib_good_nh(nh)) { + res->nh_sel = nhsel; + return; + } + if (!first) { + res->nh_sel = nhsel; + first = true; + } } endfor_nexthops(fi); - - /* Race condition: route has just become dead. */ - res->nh_sel = 0; } #endif diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 07f82e85fcc64..b0ab3d5e8e6ce 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -188,6 +188,12 @@ const __u8 ip_tos2prio[16] = { }; EXPORT_SYMBOL(ip_tos2prio); +#ifdef CONFIG_IP_ROUTE_MULTIPATH +int sysctl_fib_multipath_use_neigh = 0; +EXPORT_SYMBOL(sysctl_fib_multipath_use_neigh); + +#endif + static DEFINE_PER_CPU(struct rt_cache_stat, rt_cache_stat); #define RT_CACHE_STAT_INC(field) raw_cpu_inc(rt_cache_stat.field) diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index 3d2475749728a..78974c7b98f13 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -760,6 +760,17 @@ static struct ctl_table ipv4_table[] = { .proc_handler = proc_dointvec_minmax, .extra1 = &one }, +#ifdef CONFIG_IP_ROUTE_MULTIPATH + { + .procname = "fib_multipath_use_neigh", + .data = &sysctl_fib_multipath_use_neigh, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + .extra2 = &one, + }, +#endif { } };