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>

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 3ba2998..e649bd3 100644 (file)
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -383,22 +383,5 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev,
                ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \
                pos = rcu_dereference(pos->next))
 
-/**
- * hlist_for_each_entry_rcu_safenext - iterate over rcu list of given type
- * @tpos:      the type * to use as a loop cursor.
- * @pos:       the &struct hlist_node to use as a loop cursor.
- * @head:      the head for your list.
- * @member:    the name of the hlist_node within the struct.
- * @next:       the &struct hlist_node to use as a next cursor
- *
- * Special version of hlist_for_each_entry_rcu that make sure
- * each next pointer is fetched before each iteration.
- */
-#define hlist_for_each_entry_rcu_safenext(tpos, pos, head, member, next) \
-       for (pos = rcu_dereference((head)->first);                       \
-               pos && ({ next = pos->next; smp_rmb(); prefetch(next); 1; }) && \
-               ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \
-               pos = rcu_dereference(next))
-
 #endif /* __KERNEL__ */
 #endif

diff --git a/include/net/sock.h b/include/net/sock.h
index 8b2b821..0a63894 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -42,6 +42,7 @@
 
 #include <linux/kernel.h>
 #include <linux/list.h>
+#include <linux/list_nulls.h>
 #include <linux/timer.h>
 #include <linux/cache.h>
 #include <linux/module.h>
@@ -52,6 +53,7 @@
 #include <linux/security.h>
 
 #include <linux/filter.h>
+#include <linux/rculist_nulls.h>
 
 #include <asm/atomic.h>
 #include <net/dst.h>
@@ -106,6 +108,7 @@ struct net;
  *     @skc_reuse: %SO_REUSEADDR setting
  *     @skc_bound_dev_if: bound device index if != 0
  *     @skc_node: main hash linkage for various protocol lookup tables
+ *     @skc_nulls_node: main hash linkage for UDP/UDP-Lite protocol
  *     @skc_bind_node: bind hash linkage for various protocol lookup tables
  *     @skc_refcnt: reference count
  *     @skc_hash: hash value used with various protocol lookup tables
@@ -120,7 +123,10 @@ struct sock_common {
        volatile unsigned char  skc_state;
        unsigned char           skc_reuse;
        int                     skc_bound_dev_if;
-       struct hlist_node       skc_node;
+       union {
+               struct hlist_node       skc_node;
+               struct hlist_nulls_node skc_nulls_node;
+       };
        struct hlist_node       skc_bind_node;
        atomic_t                skc_refcnt;
        unsigned int            skc_hash;
@@ -206,6 +212,7 @@ struct sock {
 #define sk_reuse               __sk_common.skc_reuse
 #define sk_bound_dev_if                __sk_common.skc_bound_dev_if
 #define sk_node                        __sk_common.skc_node
+#define sk_nulls_node          __sk_common.skc_nulls_node
 #define sk_bind_node           __sk_common.skc_bind_node
 #define sk_refcnt              __sk_common.skc_refcnt
 #define sk_hash                        __sk_common.skc_hash
@@ -300,12 +307,30 @@ static inline struct sock *sk_head(const struct hlist_head *head)
        return hlist_empty(head) ? NULL : __sk_head(head);
 }
 
+static inline struct sock *__sk_nulls_head(const struct hlist_nulls_head *head)
+{
+       return hlist_nulls_entry(head->first, struct sock, sk_nulls_node);
+}
+
+static inline struct sock *sk_nulls_head(const struct hlist_nulls_head *head)
+{
+       return hlist_nulls_empty(head) ? NULL : __sk_nulls_head(head);
+}
+
 static inline struct sock *sk_next(const struct sock *sk)
 {
        return sk->sk_node.next ?
                hlist_entry(sk->sk_node.next, struct sock, sk_node) : NULL;
 }
 
+static inline struct sock *sk_nulls_next(const struct sock *sk)
+{
+       return (!is_a_nulls(sk->sk_nulls_node.next)) ?
+               hlist_nulls_entry(sk->sk_nulls_node.next,
+                                 struct sock, sk_nulls_node) :
+               NULL;
+}
+
 static inline int sk_unhashed(const struct sock *sk)
 {
        return hlist_unhashed(&sk->sk_node);
@@ -321,6 +346,11 @@ static __inline__ void sk_node_init(struct hlist_node *node)
        node->pprev = NULL;
 }
 
+static __inline__ void sk_nulls_node_init(struct hlist_nulls_node *node)
+{
+       node->pprev = NULL;
+}
+
 static __inline__ void __sk_del_node(struct sock *sk)
 {
        __hlist_del(&sk->sk_node);
@@ -367,18 +397,18 @@ static __inline__ int sk_del_node_init(struct sock *sk)
        return rc;
 }
 
-static __inline__ int __sk_del_node_init_rcu(struct sock *sk)
+static __inline__ int __sk_nulls_del_node_init_rcu(struct sock *sk)
 {
        if (sk_hashed(sk)) {
-               hlist_del_init_rcu(&sk->sk_node);
+               hlist_nulls_del_init_rcu(&sk->sk_nulls_node);
                return 1;
        }
        return 0;
 }
 
-static __inline__ int sk_del_node_init_rcu(struct sock *sk)
+static __inline__ int sk_nulls_del_node_init_rcu(struct sock *sk)
 {
-       int rc = __sk_del_node_init_rcu(sk);
+       int rc = __sk_nulls_del_node_init_rcu(sk);
 
        if (rc) {
                /* paranoid for a while -acme */
@@ -399,15 +429,15 @@ static __inline__ void sk_add_node(struct sock *sk, struct hlist_head *list)
        __sk_add_node(sk, list);
 }
 
-static __inline__ void __sk_add_node_rcu(struct sock *sk, struct hlist_head *list)
+static __inline__ void __sk_nulls_add_node_rcu(struct sock *sk, struct hlist_nulls_head *list)
 {
-       hlist_add_head_rcu(&sk->sk_node, list);
+       hlist_nulls_add_head_rcu(&sk->sk_nulls_node, list);
 }
 
-static __inline__ void sk_add_node_rcu(struct sock *sk, struct hlist_head *list)
+static __inline__ void sk_nulls_add_node_rcu(struct sock *sk, struct hlist_nulls_head *list)
 {
        sock_hold(sk);
-       __sk_add_node_rcu(sk, list);
+       __sk_nulls_add_node_rcu(sk, list);
 }
 
 static __inline__ void __sk_del_bind_node(struct sock *sk)
@@ -423,11 +453,16 @@ static __inline__ void sk_add_bind_node(struct sock *sk,
 
 #define sk_for_each(__sk, node, list) \
        hlist_for_each_entry(__sk, node, list, sk_node)
-#define sk_for_each_rcu_safenext(__sk, node, list, next) \
-       hlist_for_each_entry_rcu_safenext(__sk, node, list, sk_node, next)
+#define sk_nulls_for_each(__sk, node, list) \
+       hlist_nulls_for_each_entry(__sk, node, list, sk_nulls_node)
+#define sk_nulls_for_each_rcu(__sk, node, list) \
+       hlist_nulls_for_each_entry_rcu(__sk, node, list, sk_nulls_node)
 #define sk_for_each_from(__sk, node) \
        if (__sk && ({ node = &(__sk)->sk_node; 1; })) \
                hlist_for_each_entry_from(__sk, node, sk_node)
+#define sk_nulls_for_each_from(__sk, node) \
+       if (__sk && ({ node = &(__sk)->sk_nulls_node; 1; })) \
+               hlist_nulls_for_each_entry_from(__sk, node, sk_nulls_node)
 #define sk_for_each_continue(__sk, node) \
        if (__sk && ({ node = &(__sk)->sk_node; 1; })) \
                hlist_for_each_entry_continue(__sk, node, sk_node)

diff --git a/include/net/udp.h b/include/net/udp.h
index df2bfe5..90e6ce5 100644 (file)
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -51,7 +51,7 @@ struct udp_skb_cb {
 #define UDP_SKB_CB(__skb)      ((struct udp_skb_cb *)((__skb)->cb))
 
 struct udp_hslot {
-       struct hlist_head       head;
+       struct hlist_nulls_head head;
        spinlock_t              lock;
 } __attribute__((aligned(2 * sizeof(long))));
 struct udp_table {

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 54badc9..fea2d87 100644 (file)
--- 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 8dafa36..fd2d9ad 100644 (file)
--- 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) {