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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

25
net/ipv6/ipv6_sockglue.c
View File

@@ -114,9 +114,9 @@ struct ipv6_txoptions *ipv6_update_options(struct sock *sk,
}
opt = xchg(&inet6_sk(sk)->opt, opt);
} else {
write_lock(&sk->sk_dst_lock);
spin_lock(&sk->sk_dst_lock);
opt = xchg(&inet6_sk(sk)->opt, opt);
write_unlock(&sk->sk_dst_lock);
spin_unlock(&sk->sk_dst_lock);
}
sk_dst_reset(sk);
@@ -971,14 +971,13 @@ static int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
case IPV6_MTU:
{
struct dst_entry *dst;
val = 0;
lock_sock(sk);
dst = sk_dst_get(sk);
if (dst) {
rcu_read_lock();
dst = __sk_dst_get(sk);
if (dst)
val = dst_mtu(dst);
dst_release(dst);
}
release_sock(sk);
rcu_read_unlock();
if (!val)
return -ENOTCONN;
break;
@@ -1066,12 +1065,14 @@ static int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
else
val = np->mcast_hops;
dst = sk_dst_get(sk);
if (dst) {
if (val < 0)
if (val < 0) {
rcu_read_lock();
dst = __sk_dst_get(sk);
if (dst)
val = ip6_dst_hoplimit(dst);
dst_release(dst);
rcu_read_unlock();
}
if (val < 0)
val = sock_net(sk)->ipv6.devconf_all->hop_limit;
break;