[IPV4] fib_trie: rescan if key is lost during dump

Normally during a dump the key of the last dumped entry is used for
continuation, but since lock is dropped it might be lost. In that case
fallback to the old counter based N^2 behaviour.  This means the dump
will end up skipping some routes which matches what FIB_HASH does.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 33 insertions, 18 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index bd13b6f4a98..fb0713b6ffa 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -219,7 +219,7 @@ struct netlink_callback
         int             (*dump)(struct sk_buff * skb, struct netlink_callback *cb);
         int             (*done)(struct netlink_callback *cb);
         int             family;
-        long            args[5];
+        long            args[6];
 };
 
 struct netlink_notify
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index cbccafde823..35851c96bdf 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -1758,6 +1758,19 @@ static struct leaf *trie_nextleaf(struct leaf *l)
         return leaf_walk_rcu(p, c);
 }
 
+static struct leaf *trie_leafindex(struct trie *t, int index)
+{
+        struct leaf *l = trie_firstleaf(t);
+
+        while (index-- > 0) {
+                l = trie_nextleaf(l);
+                if (!l)
+                        break;
+        }
+        return l;
+}
+
+
 /*
  * Caller must hold RTNL.
  */
@@ -1863,7 +1876,7 @@ static int fn_trie_dump_fa(t_key key, int plen, struct list_head *fah,
         struct fib_alias *fa;
         __be32 xkey = htonl(key);
 
-        s_i = cb->args[4];
+        s_i = cb->args[5];
         i = 0;
 
         /* rcu_read_lock is hold by caller */
@@ -1884,12 +1897,12 @@ static int fn_trie_dump_fa(t_key key, int plen, struct list_head *fah,
                                   plen,
                                   fa->fa_tos,
                                   fa->fa_info, NLM_F_MULTI) < 0) {
-                        cb->args[4] = i;
+                        cb->args[5] = i;
                         return -1;
                 }
                 i++;
         }
-        cb->args[4] = i;
+        cb->args[5] = i;
         return skb->len;
 }
 
@@ -1900,7 +1913,7 @@ static int fn_trie_dump_leaf(struct leaf *l, struct fib_table *tb,
         struct hlist_node *node;
         int i, s_i;
 
-        s_i = cb->args[3];
+        s_i = cb->args[4];
         i = 0;
 
         /* rcu_read_lock is hold by caller */
@@ -1911,19 +1924,19 @@ static int fn_trie_dump_leaf(struct leaf *l, struct fib_table *tb,
                 }
 
                 if (i > s_i)
-                        cb->args[4] = 0;
+                        cb->args[5] = 0;
 
                 if (list_empty(&li->falh))
                         continue;
 
                 if (fn_trie_dump_fa(l->key, li->plen, &li->falh, tb, skb, cb) < 0) {
-                        cb->args[3] = i;
+                        cb->args[4] = i;
                         return -1;
                 }
                 i++;
         }
 
-        cb->args[3] = i;
+        cb->args[4] = i;
         return skb->len;
 }
 
@@ -1933,35 +1946,37 @@ static int fn_trie_dump(struct fib_table *tb, struct sk_buff *skb,
         struct leaf *l;
         struct trie *t = (struct trie *) tb->tb_data;
         t_key key = cb->args[2];
+        int count = cb->args[3];
 
         rcu_read_lock();
         /* Dump starting at last key.
          * Note: 0.0.0.0/0 (ie default) is first key.
          */
-        if (!key)
+        if (count == 0)
                 l = trie_firstleaf(t);
         else {
+                /* Normally, continue from last key, but if that is missing
+                 * fallback to using slow rescan
+                 */
                 l = fib_find_node(t, key);
-                if (!l) {
-                        /* The table changed during the dump, rather than
-                         * giving partial data, just make application retry.
-                         */
-                        rcu_read_unlock();
-                        return -EBUSY;
-                }
+                if (!l)
+                        l = trie_leafindex(t, count);
         }
 
         while (l) {
                 cb->args[2] = l->key;
                 if (fn_trie_dump_leaf(l, tb, skb, cb) < 0) {
+                        cb->args[3] = count;
                         rcu_read_unlock();
                         return -1;
                 }
 
+                ++count;
                 l = trie_nextleaf(l);
-                memset(&cb->args[3], 0,
-                       sizeof(cb->args) - 3*sizeof(cb->args[0]));
+                memset(&cb->args[4], 0,
+                       sizeof(cb->args) - 4*sizeof(cb->args[0]));
         }
+        cb->args[3] = count;
         rcu_read_unlock();
 
         return skb->len;