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>
diff --git a/net/core/dev.c b/net/core/dev.c
index 0eb79e3..ca4cdef 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2015,7 +2015,7 @@
if (dev->real_num_tx_queues > 1)
queue_index = skb_tx_hash(dev, skb);
- if (sk && sk->sk_dst_cache)
+ if (sk && rcu_dereference_check(sk->sk_dst_cache, 1))
sk_tx_queue_set(sk, queue_index);
}
}
diff --git a/net/core/sock.c b/net/core/sock.c
index c5812bb..7effa1e 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -364,11 +364,11 @@
struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie)
{
- struct dst_entry *dst = sk->sk_dst_cache;
+ struct dst_entry *dst = __sk_dst_get(sk);
if (dst && dst->obsolete && dst->ops->check(dst, cookie) == NULL) {
sk_tx_queue_clear(sk);
- sk->sk_dst_cache = NULL;
+ rcu_assign_pointer(sk->sk_dst_cache, NULL);
dst_release(dst);
return NULL;
}
@@ -1157,7 +1157,7 @@
skb_queue_head_init(&newsk->sk_async_wait_queue);
#endif
- rwlock_init(&newsk->sk_dst_lock);
+ spin_lock_init(&newsk->sk_dst_lock);
rwlock_init(&newsk->sk_callback_lock);
lockdep_set_class_and_name(&newsk->sk_callback_lock,
af_callback_keys + newsk->sk_family,
@@ -1898,7 +1898,7 @@
} else
sk->sk_sleep = NULL;
- rwlock_init(&sk->sk_dst_lock);
+ spin_lock_init(&sk->sk_dst_lock);
rwlock_init(&sk->sk_callback_lock);
lockdep_set_class_and_name(&sk->sk_callback_lock,
af_callback_keys + sk->sk_family,
diff --git a/net/dccp/timer.c b/net/dccp/timer.c
index bbfeb5e..1a9aa05d 100644
--- a/net/dccp/timer.c
+++ b/net/dccp/timer.c
@@ -38,7 +38,7 @@
if (sk->sk_state == DCCP_REQUESTING || sk->sk_state == DCCP_PARTOPEN) {
if (icsk->icsk_retransmits != 0)
- dst_negative_advice(&sk->sk_dst_cache, sk);
+ dst_negative_advice(sk);
retry_until = icsk->icsk_syn_retries ?
: sysctl_dccp_request_retries;
} else {
@@ -63,7 +63,7 @@
Golden words :-).
*/
- dst_negative_advice(&sk->sk_dst_cache, sk);
+ dst_negative_advice(sk);
}
retry_until = sysctl_dccp_retries2;
diff --git a/net/decnet/af_decnet.c b/net/decnet/af_decnet.c
index 2b494fa..55e3b6b 100644
--- a/net/decnet/af_decnet.c
+++ b/net/decnet/af_decnet.c
@@ -446,7 +446,7 @@
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 @@
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 @@
}
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;
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index a0beb32b..193dcd6 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -154,7 +154,7 @@
WARN_ON(sk->sk_forward_alloc);
kfree(inet->opt);
- dst_release(sk->sk_dst_cache);
+ dst_release(rcu_dereference_check(sk->sk_dst_cache, 1));
sk_refcnt_debug_dec(sk);
}
EXPORT_SYMBOL(inet_sock_destruct);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4000b10..ae3ec15 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3710,7 +3710,7 @@
}
if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
- dst_confirm(sk->sk_dst_cache);
+ dst_confirm(__sk_dst_get(sk));
return 1;
@@ -5833,7 +5833,7 @@
if (tp->snd_una == tp->write_seq) {
tcp_set_state(sk, TCP_FIN_WAIT2);
sk->sk_shutdown |= SEND_SHUTDOWN;
- dst_confirm(sk->sk_dst_cache);
+ dst_confirm(__sk_dst_get(sk));
if (!sock_flag(sk, SOCK_DEAD))
/* Wake up lingering close() */
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 8a0ab29..c732be0 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -172,14 +172,14 @@
if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
if (icsk->icsk_retransmits)
- dst_negative_advice(&sk->sk_dst_cache, sk);
+ dst_negative_advice(sk);
retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
} else {
if (retransmits_timed_out(sk, sysctl_tcp_retries1)) {
/* Black hole detection */
tcp_mtu_probing(icsk, sk);
- dst_negative_advice(&sk->sk_dst_cache, sk);
+ dst_negative_advice(sk);
}
retry_until = sysctl_tcp_retries2;
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 33f60fc..1160400 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -114,9 +114,9 @@
}
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 @@
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 @@
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;