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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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4
include/net/ip6_route.h
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@@ -152,9 +152,9 @@ static inline void __ip6_dst_store(struct sock *sk, struct dst_entry *dst,
static inline void ip6_dst_store(struct sock *sk, struct dst_entry *dst,
struct in6_addr *daddr, struct in6_addr *saddr)
{
write_lock(&sk->sk_dst_lock);
spin_lock(&sk->sk_dst_lock);
__ip6_dst_store(sk, dst, daddr, saddr);
write_unlock(&sk->sk_dst_lock);
spin_unlock(&sk->sk_dst_lock);
}
static inline int ipv6_unicast_destination(struct sk_buff *skb)