net: sk_dst_cache RCUification

With latest CONFIG_PROVE_RCU stuff, I felt more comfortable to make this
work.

sk->sk_dst_cache is currently protected by a rwlock (sk_dst_lock)

This rwlock is readlocked for a very small amount of time, and dst
entries are already freed after RCU grace period. This calls for RCU
again :)

This patch converts sk_dst_lock to a spinlock, and use RCU for readers.

__sk_dst_get() is supposed to be called with rcu_read_lock() or if
socket locked by user, so use appropriate rcu_dereference_check()
condition (rcu_read_lock_held() || sock_owned_by_user(sk))

This patch avoids two atomic ops per tx packet on UDP connected sockets,
for example, and permits sk_dst_lock to be much less dirtied.

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

1 files changed, 0 insertions, 15 deletions

diff --git a/include/net/dst.h b/include/net/dst.h
index ce078cda6b74..aac5a5fcfda9 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -225,21 +225,6 @@ static inline void dst_confirm(struct dst_entry *dst)
                 neigh_confirm(dst->neighbour);
 }
 
-static inline void dst_negative_advice(struct dst_entry **dst_p,
-                                       struct sock *sk)
-{
-        struct dst_entry * dst = *dst_p;
-        if (dst && dst->ops->negative_advice) {
-                *dst_p = dst->ops->negative_advice(dst);
-
-                if (dst != *dst_p) {
-                        extern void sk_reset_txq(struct sock *sk);
-
-                        sk_reset_txq(sk);
-                }
-        }
-}
-
 static inline void dst_link_failure(struct sk_buff *skb)
 {
         struct dst_entry *dst = skb_dst(skb);