ipv4: RCU conversion of ip_route_input_slow/ip_route_input_mc

Avoid two atomic ops on struct in_device refcount per incoming packet,
if slow path taken, (or route cache disabled)

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

1 files changed, 17 insertions, 18 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index d377b45005fc..1cfe0d199e7c 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1843,13 +1843,14 @@ static void rt_set_nexthop(struct rtable *rt, struct fib_result *res, u32 itag)
         rt->rt_type = res->type;
 }
 
+/* called in rcu_read_lock() section */
 static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                                 u8 tos, struct net_device *dev, int our)
 {
-        unsigned hash;
+        unsigned int hash;
         struct rtable *rth;
         __be32 spec_dst;
-        struct in_device *in_dev = in_dev_get(dev);
+        struct in_device *in_dev = __in_dev_get_rcu(dev);
         u32 itag = 0;
         int err;
 
@@ -1914,18 +1915,14 @@ static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 #endif
         RT_CACHE_STAT_INC(in_slow_mc);
 
-        in_dev_put(in_dev);
         hash = rt_hash(daddr, saddr, dev->ifindex, rt_genid(dev_net(dev)));
         return rt_intern_hash(hash, rth, NULL, skb, dev->ifindex);
 
 e_nobufs:
-        in_dev_put(in_dev);
         return -ENOBUFS;
-
 e_inval:
-        err = -EINVAL;
+        return -EINVAL;
 e_err:
-        in_dev_put(in_dev);
         return err;
 }
 
@@ -2101,7 +2098,7 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                                u8 tos, struct net_device *dev)
 {
         struct fib_result res;
-        struct in_device *in_dev = in_dev_get(dev);
+        struct in_device *in_dev = __in_dev_get_rcu(dev);
         struct flowi fl = { .nl_u = { .ip4_u =
                                       { .daddr = daddr,
                                         .saddr = saddr,
@@ -2179,7 +2176,6 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 
         err = ip_mkroute_input(skb, &res, &fl, in_dev, daddr, saddr, tos);
 done:
-        in_dev_put(in_dev);
         if (free_res)
                 fib_res_put(&res);
 out:    return err;
@@ -2288,16 +2284,18 @@ int ip_route_input_common(struct sk_buff *skb, __be32 daddr, __be32 saddr,
         unsigned        hash;
         int iif = dev->ifindex;
         struct net *net;
+        int res;
 
         net = dev_net(dev);
 
+        rcu_read_lock();
+
         if (!rt_caching(net))
                 goto skip_cache;
 
         tos &= IPTOS_RT_MASK;
         hash = rt_hash(daddr, saddr, iif, rt_genid(net));
 
-        rcu_read_lock();
         for (rth = rcu_dereference(rt_hash_table[hash].chain); rth;
              rth = rcu_dereference(rth->u.dst.rt_next)) {
                 if ((((__force u32)rth->fl.fl4_dst ^ (__force u32)daddr) |
@@ -2321,7 +2319,6 @@ int ip_route_input_common(struct sk_buff *skb, __be32 daddr, __be32 saddr,
                 }
                 RT_CACHE_STAT_INC(in_hlist_search);
         }
-        rcu_read_unlock();
 
 skip_cache:
         /* Multicast recognition logic is moved from route cache to here.
@@ -2336,12 +2333,11 @@ skip_cache:
            route cache entry is created eventually.
          */
         if (ipv4_is_multicast(daddr)) {
-                struct in_device *in_dev;
+                struct in_device *in_dev = __in_dev_get_rcu(dev);
 
-                rcu_read_lock();
-                if ((in_dev = __in_dev_get_rcu(dev)) != NULL) {
+                if (in_dev) {
                         int our = ip_check_mc(in_dev, daddr, saddr,
-                                ip_hdr(skb)->protocol);
+                                              ip_hdr(skb)->protocol);
                         if (our
 #ifdef CONFIG_IP_MROUTE
                                 ||
@@ -2349,15 +2345,18 @@ skip_cache:
                              IN_DEV_MFORWARD(in_dev))
 #endif
                            ) {
+                                int res = ip_route_input_mc(skb, daddr, saddr,
+                                                            tos, dev, our);
                                 rcu_read_unlock();
-                                return ip_route_input_mc(skb, daddr, saddr,
-                                                         tos, dev, our);
+                                return res;
                         }
                 }
                 rcu_read_unlock();
                 return -EINVAL;
         }
-        return ip_route_input_slow(skb, daddr, saddr, tos, dev);
+        res = ip_route_input_slow(skb, daddr, saddr, tos, dev);
+        rcu_read_unlock();
+        return res;
 }
 EXPORT_SYMBOL(ip_route_input_common);