ipv6: speedup inet6_dump_ifinfo()

When handling large number of netdevice, inet6_dump_ifinfo()
is very slow because it has O(N^2) complexity.

Instead of scanning one single list, we can use the 256 sub lists
of the dev_index hash table, and RCU lookups.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 28 insertions, 17 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 024bba30de21..f9f7fd6ee1f3 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3823,28 +3823,39 @@ nla_put_failure:
 static int inet6_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 {
         struct net *net = sock_net(skb->sk);
-        int idx, err;
-        int s_idx = cb->args[0];
+        int h, s_h;
+        int idx = 0, err, s_idx;
         struct net_device *dev;
         struct inet6_dev *idev;
+        struct hlist_head *head;
+        struct hlist_node *node;
 
-        read_lock(&dev_base_lock);
-        idx = 0;
-        for_each_netdev(net, dev) {
-                if (idx < s_idx)
-                        goto cont;
-                if ((idev = in6_dev_get(dev)) == NULL)
-                        goto cont;
-                err = inet6_fill_ifinfo(skb, idev, NETLINK_CB(cb->skb).pid,
-                                cb->nlh->nlmsg_seq, RTM_NEWLINK, NLM_F_MULTI);
-                in6_dev_put(idev);
-                if (err <= 0)
-                        break;
+        s_h = cb->args[0];
+        s_idx = cb->args[1];
+
+        rcu_read_lock();
+        for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
+                idx = 0;
+                head = &net->dev_index_head[h];
+                hlist_for_each_entry_rcu(dev, node, head, index_hlist) {
+                        if (idx < s_idx)
+                                goto cont;
+                        idev = __in6_dev_get(dev);
+                        if (!idev)
+                                goto cont;
+                        if (inet6_fill_ifinfo(skb, idev,
+                                              NETLINK_CB(cb->skb).pid,
+                                              cb->nlh->nlmsg_seq,
+                                              RTM_NEWLINK, NLM_F_MULTI) <= 0)
+                                goto out;
 cont:
-                idx++;
+                        idx++;
+                }
         }
-        read_unlock(&dev_base_lock);
-        cb->args[0] = idx;
+out:
+        rcu_read_unlock();
+        cb->args[1] = idx;
+        cb->args[0] = h;
 
         return skb->len;
 }