ipv6: Fix sporadic sendmsg -EINVAL when sending to multicast groups.

Thanks to excellent diagnosis by Eduard Guzovsky.

The core problem is that on a network with lots of active
multicast traffic, the neighbour cache can fill up.  If
we try to allocate a new route and thus neighbour cache
entry, the bog-standard GC attempt the neighbour layer does
in ineffective because route entries hold a reference
to the existing neighbour entries and GC can only liberate
entries with no references.

IPV4 already has a way to handle this, by doing a route cache
GC in such situations (when neigh attach returns -ENOBUFS).

So simply mimick this on the ipv6 side.

Tested-by: Eduard Guzovsky <eguzovsky@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/ndisc.h b/include/net/ndisc.h
index ce532f2222ce723daf21eaea7429bcbb5a26b4a8..1459ed3e2697b495bb37226c8190b7f81d428c3c 100644 (file)
--- a/include/net/ndisc.h
+++ b/include/net/ndisc.h
@@ -155,9 +155,9 @@ static inline struct neighbour * ndisc_get_neigh(struct net_device *dev, const s
 {
 
        if (dev)
-               return __neigh_lookup(&nd_tbl, addr, dev, 1);
+               return __neigh_lookup_errno(&nd_tbl, addr, dev);
 
-       return NULL;
+       return ERR_PTR(-ENODEV);
 }
 
 

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 18c486cf498756b5a4536d17798854ba137ba37f..76f06b94ab9f61a6e7ed6c844feeba21cae47e9a 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -627,6 +627,9 @@ static struct rt6_info *rt6_alloc_cow(struct rt6_info *ort, struct in6_addr *dad
        rt = ip6_rt_copy(ort);
 
        if (rt) {
+               struct neighbour *neigh;
+               int attempts = !in_softirq();
+
                if (!(rt->rt6i_flags&RTF_GATEWAY)) {
                        if (rt->rt6i_dst.plen != 128 &&
                            ipv6_addr_equal(&rt->rt6i_dst.addr, daddr))
@@ -646,7 +649,35 @@ static struct rt6_info *rt6_alloc_cow(struct rt6_info *ort, struct in6_addr *dad
                }
 #endif
 
-               rt->rt6i_nexthop = ndisc_get_neigh(rt->rt6i_dev, &rt->rt6i_gateway);
+       retry:
+               neigh = ndisc_get_neigh(rt->rt6i_dev, &rt->rt6i_gateway);
+               if (IS_ERR(neigh)) {
+                       struct net *net = dev_net(rt->rt6i_dev);
+                       int saved_rt_min_interval =
+                               net->ipv6.sysctl.ip6_rt_gc_min_interval;
+                       int saved_rt_elasticity =
+                               net->ipv6.sysctl.ip6_rt_gc_elasticity;
+
+                       if (attempts-- > 0) {
+                               net->ipv6.sysctl.ip6_rt_gc_elasticity = 1;
+                               net->ipv6.sysctl.ip6_rt_gc_min_interval = 0;
+
+                               ip6_dst_gc(net->ipv6.ip6_dst_ops);
+
+                               net->ipv6.sysctl.ip6_rt_gc_elasticity =
+                                       saved_rt_elasticity;
+                               net->ipv6.sysctl.ip6_rt_gc_min_interval =
+                                       saved_rt_min_interval;
+                               goto retry;
+                       }
+
+                       if (net_ratelimit())
+                               printk(KERN_WARNING
+                                      "Neighbour table overflow.\n");
+                       dst_free(&rt->u.dst);
+                       return NULL;
+               }
+               rt->rt6i_nexthop = neigh;
 
        }
 
@@ -945,8 +976,11 @@ struct dst_entry *icmp6_dst_alloc(struct net_device *dev,
        dev_hold(dev);
        if (neigh)
                neigh_hold(neigh);
-       else
+       else {
                neigh = ndisc_get_neigh(dev, addr);
+               if (IS_ERR(neigh))
+                       neigh = NULL;
+       }
 
        rt->rt6i_dev      = dev;
        rt->rt6i_idev     = idev;
@@ -1887,6 +1921,7 @@ struct rt6_info *addrconf_dst_alloc(struct inet6_dev *idev,
 {
        struct net *net = dev_net(idev->dev);
        struct rt6_info *rt = ip6_dst_alloc(net->ipv6.ip6_dst_ops);
+       struct neighbour *neigh;
 
        if (rt == NULL)
                return ERR_PTR(-ENOMEM);
@@ -1909,11 +1944,18 @@ struct rt6_info *addrconf_dst_alloc(struct inet6_dev *idev,
                rt->rt6i_flags |= RTF_ANYCAST;
        else
                rt->rt6i_flags |= RTF_LOCAL;
-       rt->rt6i_nexthop = ndisc_get_neigh(rt->rt6i_dev, &rt->rt6i_gateway);
-       if (rt->rt6i_nexthop == NULL) {
+       neigh = ndisc_get_neigh(rt->rt6i_dev, &rt->rt6i_gateway);
+       if (IS_ERR(neigh)) {
                dst_free(&rt->u.dst);
-               return ERR_PTR(-ENOMEM);
+
+               /* We are casting this because that is the return
+                * value type.  But an errno encoded pointer is the
+                * same regardless of the underlying pointer type,
+                * and that's what we are returning.  So this is OK.
+                */
+               return (struct rt6_info *) neigh;
        }
+       rt->rt6i_nexthop = neigh;
 
        ipv6_addr_copy(&rt->rt6i_dst.addr, addr);
        rt->rt6i_dst.plen = 128;