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net: sk_dst_cache RCUification

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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>
This commit is contained in:
Eric Dumazet 2010-04-08 23:03:29 +00:00 • committed by David S. Miller
parent 7a161ea924
commit b6c6712a42
11 changed files with 60 additions and 61 deletions
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15
include/net/dst.h
View file

@ -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);