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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
Download Patch File Download Diff File Expand all files Collapse all files

6
net/decnet/af_decnet.c
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@ -446,7 +446,7 @@ static void dn_destruct(struct sock *sk)
skb_queue_purge(&scp->other_xmit_queue);
skb_queue_purge(&scp->other_receive_queue);
dst_release(xchg(&sk->sk_dst_cache, NULL));
dst_release(rcu_dereference_check(sk->sk_dst_cache, 1));
}
static int dn_memory_pressure;
@ -1105,7 +1105,7 @@ static int dn_accept(struct socket *sock, struct socket *newsock, int flags)
release_sock(sk);
dst = skb_dst(skb);
dst_release(xchg(&newsk->sk_dst_cache, dst));
sk_dst_set(newsk, dst);
skb_dst_set(skb, NULL);
DN_SK(newsk)->state = DN_CR;
@ -1956,7 +1956,7 @@ static int dn_sendmsg(struct kiocb *iocb, struct socket *sock,
}
if ((flags & MSG_TRYHARD) && sk->sk_dst_cache)
dst_negative_advice(&sk->sk_dst_cache, sk);
dst_negative_advice(sk);
mss = scp->segsize_rem;
fctype = scp->services_rem & NSP_FC_MASK;