udp: Use hlist_nulls in UDP RCU code

This is a straightforward patch, using hlist_nulls infrastructure.

RCUification already done on UDP two weeks ago.

Using hlist_nulls permits us to avoid some memory barriers, both
at lookup time and delete time.

Patch is large because it adds new macros to include/net/sock.h.
These macros will be used by TCP & DCCP in next patch.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 36 insertions, 37 deletions

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 54badc9a019d..fea2d873dd41 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -127,9 +127,9 @@ static int udp_lib_lport_inuse(struct net *net, __u16 num,
                                                  const struct sock *sk2))
 {
         struct sock *sk2;
-        struct hlist_node *node;
+        struct hlist_nulls_node *node;
 
-        sk_for_each(sk2, node, &hslot->head)
+        sk_nulls_for_each(sk2, node, &hslot->head)
                 if (net_eq(sock_net(sk2), net)                  &&
                     sk2 != sk                                   &&
                     sk2->sk_hash == num                         &&
@@ -189,12 +189,7 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
         inet_sk(sk)->num = snum;
         sk->sk_hash = snum;
         if (sk_unhashed(sk)) {
-                /*
-                 * We need that previous write to sk->sk_hash committed
-                 * before write to sk->next done in following add_node() variant
-                 */
-                smp_wmb();
-                sk_add_node_rcu(sk, &hslot->head);
+                sk_nulls_add_node_rcu(sk, &hslot->head);
                 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
         }
         error = 0;
@@ -261,7 +256,7 @@ static struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
                 int dif, struct udp_table *udptable)
 {
         struct sock *sk, *result;
-        struct hlist_node *node, *next;
+        struct hlist_nulls_node *node;
         unsigned short hnum = ntohs(dport);
         unsigned int hash = udp_hashfn(net, hnum);
         struct udp_hslot *hslot = &udptable->hash[hash];
@@ -271,13 +266,7 @@ static struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
 begin:
         result = NULL;
         badness = -1;
-        sk_for_each_rcu_safenext(sk, node, &hslot->head, next) {
-                /*
-                 * lockless reader, and SLAB_DESTROY_BY_RCU items:
-                 * We must check this item was not moved to another chain
-                 */
-                if (udp_hashfn(net, sk->sk_hash) != hash)
-                        goto begin;
+        sk_nulls_for_each_rcu(sk, node, &hslot->head) {
                 score = compute_score(sk, net, saddr, hnum, sport,
                                       daddr, dport, dif);
                 if (score > badness) {
@@ -285,6 +274,14 @@ begin:
                         badness = score;
                 }
         }
+        /*
+         * if the nulls value we got at the end of this lookup is
+         * not the expected one, we must restart lookup.
+         * We probably met an item that was moved to another chain.
+         */
+        if (get_nulls_value(node) != hash)
+                goto begin;
+
         if (result) {
                 if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
                         result = NULL;
@@ -325,11 +322,11 @@ static inline struct sock *udp_v4_mcast_next(struct net *net, struct sock *sk,
                                              __be16 rmt_port, __be32 rmt_addr,
                                              int dif)
 {
-        struct hlist_node *node;
+        struct hlist_nulls_node *node;
         struct sock *s = sk;
         unsigned short hnum = ntohs(loc_port);
 
-        sk_for_each_from(s, node) {
+        sk_nulls_for_each_from(s, node) {
                 struct inet_sock *inet = inet_sk(s);
 
                 if (!net_eq(sock_net(s), net)                           ||
@@ -977,7 +974,7 @@ void udp_lib_unhash(struct sock *sk)
         struct udp_hslot *hslot = &udptable->hash[hash];
 
         spin_lock_bh(&hslot->lock);
-        if (sk_del_node_init_rcu(sk)) {
+        if (sk_nulls_del_node_init_rcu(sk)) {
                 inet_sk(sk)->num = 0;
                 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
         }
@@ -1130,7 +1127,7 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
         int dif;
 
         spin_lock(&hslot->lock);
-        sk = sk_head(&hslot->head);
+        sk = sk_nulls_head(&hslot->head);
         dif = skb->dev->ifindex;
         sk = udp_v4_mcast_next(net, sk, uh->dest, daddr, uh->source, saddr, dif);
         if (sk) {
@@ -1139,7 +1136,7 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
                 do {
                         struct sk_buff *skb1 = skb;
 
-                        sknext = udp_v4_mcast_next(net, sk_next(sk), uh->dest,
+                        sknext = udp_v4_mcast_next(net, sk_nulls_next(sk), uh->dest,
                                                    daddr, uh->source, saddr,
                                                    dif);
                         if (sknext)
@@ -1560,10 +1557,10 @@ static struct sock *udp_get_first(struct seq_file *seq, int start)
         struct net *net = seq_file_net(seq);
 
         for (state->bucket = start; state->bucket < UDP_HTABLE_SIZE; ++state->bucket) {
-                struct hlist_node *node;
+                struct hlist_nulls_node *node;
                 struct udp_hslot *hslot = &state->udp_table->hash[state->bucket];
                 spin_lock_bh(&hslot->lock);
-                sk_for_each(sk, node, &hslot->head) {
+                sk_nulls_for_each(sk, node, &hslot->head) {
                         if (!net_eq(sock_net(sk), net))
                                 continue;
                         if (sk->sk_family == state->family)
@@ -1582,7 +1579,7 @@ static struct sock *udp_get_next(struct seq_file *seq, struct sock *sk)
         struct net *net = seq_file_net(seq);
 
         do {
-                sk = sk_next(sk);
+                sk = sk_nulls_next(sk);
         } while (sk && (!net_eq(sock_net(sk), net) || sk->sk_family != state->family));
 
         if (!sk) {
@@ -1753,7 +1750,7 @@ void __init udp_table_init(struct udp_table *table)
         int i;
 
         for (i = 0; i < UDP_HTABLE_SIZE; i++) {
-                INIT_HLIST_HEAD(&table->hash[i].head);
+                INIT_HLIST_NULLS_HEAD(&table->hash[i].head, i);
                 spin_lock_init(&table->hash[i].lock);
         }
 }
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 8dafa36b1ba5..fd2d9ad4a8a3 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -98,7 +98,7 @@ static struct sock *__udp6_lib_lookup(struct net *net,
                                       int dif, struct udp_table *udptable)
 {
         struct sock *sk, *result;
-        struct hlist_node *node, *next;
+        struct hlist_nulls_node *node;
         unsigned short hnum = ntohs(dport);
         unsigned int hash = udp_hashfn(net, hnum);
         struct udp_hslot *hslot = &udptable->hash[hash];
@@ -108,19 +108,21 @@ static struct sock *__udp6_lib_lookup(struct net *net,
 begin:
         result = NULL;
         badness = -1;
-        sk_for_each_rcu_safenext(sk, node, &hslot->head, next) {
-                /*
-                 * lockless reader, and SLAB_DESTROY_BY_RCU items:
-                 * We must check this item was not moved to another chain
-                 */
-                if (udp_hashfn(net, sk->sk_hash) != hash)
-                        goto begin;
+        sk_nulls_for_each_rcu(sk, node, &hslot->head) {
                 score = compute_score(sk, net, hnum, saddr, sport, daddr, dport, dif);
                 if (score > badness) {
                         result = sk;
                         badness = score;
                 }
         }
+        /*
+         * if the nulls value we got at the end of this lookup is
+         * not the expected one, we must restart lookup.
+         * We probably met an item that was moved to another chain.
+         */
+        if (get_nulls_value(node) != hash)
+                goto begin;
+
         if (result) {
                 if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
                         result = NULL;
@@ -374,11 +376,11 @@ static struct sock *udp_v6_mcast_next(struct net *net, struct sock *sk,
                                       __be16 rmt_port, struct in6_addr *rmt_addr,
                                       int dif)
 {
-        struct hlist_node *node;
+        struct hlist_nulls_node *node;
         struct sock *s = sk;
         unsigned short num = ntohs(loc_port);
 
-        sk_for_each_from(s, node) {
+        sk_nulls_for_each_from(s, node) {
                 struct inet_sock *inet = inet_sk(s);
 
                 if (!net_eq(sock_net(s), net))
@@ -423,7 +425,7 @@ static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
         int dif;
 
         spin_lock(&hslot->lock);
-        sk = sk_head(&hslot->head);
+        sk = sk_nulls_head(&hslot->head);
         dif = inet6_iif(skb);
         sk = udp_v6_mcast_next(net, sk, uh->dest, daddr, uh->source, saddr, dif);
         if (!sk) {
@@ -432,7 +434,7 @@ static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
         }
 
         sk2 = sk;
-        while ((sk2 = udp_v6_mcast_next(net, sk_next(sk2), uh->dest, daddr,
+        while ((sk2 = udp_v6_mcast_next(net, sk_nulls_next(sk2), uh->dest, daddr,
                                         uh->source, saddr, dif))) {
                 struct sk_buff *buff = skb_clone(skb, GFP_ATOMIC);
                 if (buff) {