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/include/net/dst.h b/include/net/dst.h
index ce078cd..aac5a5f 100644 (file)
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -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);

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 68f6783..278312c 100644 (file)
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -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)

diff --git a/include/net/sock.h b/include/net/sock.h
index b4603cd..56df440 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -262,7 +262,7 @@ struct sock {
 #ifdef CONFIG_XFRM
        struct xfrm_policy      *sk_policy[2];
 #endif
-       rwlock_t                sk_dst_lock;
+       spinlock_t              sk_dst_lock;
        atomic_t                sk_rmem_alloc;
        atomic_t                sk_wmem_alloc;
        atomic_t                sk_omem_alloc;
@@ -1192,7 +1192,8 @@ extern unsigned long sock_i_ino(struct sock *sk);
 static inline struct dst_entry *
 __sk_dst_get(struct sock *sk)
 {
-       return sk->sk_dst_cache;
+       return rcu_dereference_check(sk->sk_dst_cache, rcu_read_lock_held() ||
+                                                      sock_owned_by_user(sk));
 }
 
 static inline struct dst_entry *
@@ -1200,50 +1201,62 @@ sk_dst_get(struct sock *sk)
 {
        struct dst_entry *dst;
 
-       read_lock(&sk->sk_dst_lock);
-       dst = sk->sk_dst_cache;
+       rcu_read_lock();
+       dst = rcu_dereference(sk->sk_dst_cache);
        if (dst)
                dst_hold(dst);
-       read_unlock(&sk->sk_dst_lock);
+       rcu_read_unlock();
        return dst;
 }
 
+extern void sk_reset_txq(struct sock *sk);
+
+static inline void dst_negative_advice(struct sock *sk)
+{
+       struct dst_entry *ndst, *dst = __sk_dst_get(sk);
+
+       if (dst && dst->ops->negative_advice) {
+               ndst = dst->ops->negative_advice(dst);
+
+               if (ndst != dst) {
+                       rcu_assign_pointer(sk->sk_dst_cache, ndst);
+                       sk_reset_txq(sk);
+               }
+       }
+}
+
 static inline void
 __sk_dst_set(struct sock *sk, struct dst_entry *dst)
 {
        struct dst_entry *old_dst;
 
        sk_tx_queue_clear(sk);
-       old_dst = sk->sk_dst_cache;
-       sk->sk_dst_cache = dst;
+       old_dst = rcu_dereference_check(sk->sk_dst_cache,
+                                       lockdep_is_held(&sk->sk_dst_lock));
+       rcu_assign_pointer(sk->sk_dst_cache, dst);
        dst_release(old_dst);
 }
 
 static inline void
 sk_dst_set(struct sock *sk, struct dst_entry *dst)
 {
-       write_lock(&sk->sk_dst_lock);
+       spin_lock(&sk->sk_dst_lock);
        __sk_dst_set(sk, dst);
-       write_unlock(&sk->sk_dst_lock);
+       spin_unlock(&sk->sk_dst_lock);
 }
 
 static inline void
 __sk_dst_reset(struct sock *sk)
 {
-       struct dst_entry *old_dst;
-
-       sk_tx_queue_clear(sk);
-       old_dst = sk->sk_dst_cache;
-       sk->sk_dst_cache = NULL;
-       dst_release(old_dst);
+       __sk_dst_set(sk, NULL);
 }
 
 static inline void
 sk_dst_reset(struct sock *sk)
 {
-       write_lock(&sk->sk_dst_lock);
+       spin_lock(&sk->sk_dst_lock);
        __sk_dst_reset(sk);
-       write_unlock(&sk->sk_dst_lock);
+       spin_unlock(&sk->sk_dst_lock);
 }
 
 extern struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie);

diff --git a/net/core/dev.c b/net/core/dev.c
index 0eb79e3..ca4cdef 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2015,7 +2015,7 @@ static struct netdev_queue *dev_pick_tx(struct net_device *dev,
                        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 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -364,11 +364,11 @@ EXPORT_SYMBOL(sk_reset_txq);
 
 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 @@ struct sock *sk_clone(const struct sock *sk, const gfp_t priority)
                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 @@ void sock_init_data(struct socket *sock, struct sock *sk)
        } 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..1a9aa05 100644 (file)
--- a/net/dccp/timer.c
+++ b/net/dccp/timer.c
@@ -38,7 +38,7 @@ static int dccp_write_timeout(struct sock *sk)
 
        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 @@ static int dccp_write_timeout(struct sock *sk)
                           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 (file)
--- a/net/decnet/af_decnet.c
+++ b/net/decnet/af_decnet.c
@@ -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;

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index a0beb32..193dcd6 100644 (file)
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -154,7 +154,7 @@ void inet_sock_destruct(struct sock *sk)
        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 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3710,7 +3710,7 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
        }
 
        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 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                        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 (file)
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -172,14 +172,14 @@ static int tcp_write_timeout(struct sock *sk)
 
        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 (file)
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -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;