ipv4: Restore old dst_free() behavior.

commit 404e0a8b6a55 (net: ipv4: fix RCU races on dst refcounts) tried
to solve a race but added a problem at device/fib dismantle time :

We really want to call dst_free() as soon as possible, even if sockets
still have dst in their cache.
dst_release() calls in free_fib_info_rcu() are not welcomed.

Root of the problem was that now we also cache output routes (in
nh_rth_output), we must use call_rcu() instead of call_rcu_bh() in
rt_free(), because output route lookups are done in process context.

Based on feedback and initial patch from David Miller (adding another
call_rcu_bh() call in fib, but it appears it was not the right fix)

I left the inet_sk_rx_dst_set() helper and added __rcu attributes
to nh_rth_output and nh_rth_input to better document what is going on in
this code.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 7 deletions

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index e3fd34c83ac9..83b567fe1941 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -253,13 +253,9 @@ static inline void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb
 {
         struct dst_entry *dst = skb_dst(skb);
 
-        if (atomic_inc_not_zero(&dst->__refcnt)) {
-                if (!(dst->flags & DST_RCU_FREE))
-                        dst->flags |= DST_RCU_FREE;
-
-                sk->sk_rx_dst = dst;
-                inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
-        }
+        dst_hold(dst);
+        sk->sk_rx_dst = dst;
+        inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
 }
 
 #endif  /* _INET_SOCK_H */