ipv4: use rcu in ip_fib_check_default()

fib_info_devhash[] is not resized in fib_info_hash_move().

fib_nh structs are already freed after an rcu grace period.

This will allow to remove fib_info_lock in the following patch.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20241004134720.579244-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 1219d1b325910322dd978f3962a4cafa8e8db10b..e0ffb4ffd95d0f9ebc796c3129bc2f494fb478dd 100644 (file)
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -275,7 +275,7 @@ void fib_release_info(struct fib_info *fi)
                        change_nexthops(fi) {
                                if (!nexthop_nh->fib_nh_dev)
                                        continue;
-                               hlist_del(&nexthop_nh->nh_hash);
+                               hlist_del_rcu(&nexthop_nh->nh_hash);
                        } endfor_nexthops(fi)
                }
                /* Paired with READ_ONCE() from fib_table_lookup() */
@@ -431,28 +431,23 @@ static struct fib_info *fib_find_info(struct fib_info *nfi)
 }
 
 /* Check, that the gateway is already configured.
- * Used only by redirect accept routine.
+ * Used only by redirect accept routine, under rcu_read_lock();
  */
 int ip_fib_check_default(__be32 gw, struct net_device *dev)
 {
        struct hlist_head *head;
        struct fib_nh *nh;
 
-       spin_lock(&fib_info_lock);
-
        head = fib_info_devhash_bucket(dev);
 
-       hlist_for_each_entry(nh, head, nh_hash) {
+       hlist_for_each_entry_rcu(nh, head, nh_hash) {
                if (nh->fib_nh_dev == dev &&
                    nh->fib_nh_gw4 == gw &&
                    !(nh->fib_nh_flags & RTNH_F_DEAD)) {
-                       spin_unlock(&fib_info_lock);
                        return 0;
                }
        }
 
-       spin_unlock(&fib_info_lock);
-
        return -1;
 }
 
@@ -1606,7 +1601,7 @@ link_it:
                        if (!nexthop_nh->fib_nh_dev)
                                continue;
                        head = fib_info_devhash_bucket(nexthop_nh->fib_nh_dev);
-                       hlist_add_head(&nexthop_nh->nh_hash, head);
+                       hlist_add_head_rcu(&nexthop_nh->nh_hash, head);
                } endfor_nexthops(fi)
        }
        spin_unlock_bh(&fib_info_lock);