udp: introduce struct udp_table and multiple spinlocks

UDP sockets are hashed in a 128 slots hash table.

This hash table is protected by *one* rwlock.

This rwlock is readlocked each time an incoming UDP message is handled.

This rwlock is writelocked each time a socket must be inserted in
hash table (bind time), or deleted from this table (close time)

This is not scalable on SMP machines :

1) Even in read mode, lock() and unlock() are atomic operations and
 must dirty a contended cache line, shared by all cpus.

2) A writer might be starved if many readers are 'in flight'. This can
 happen on a machine with some NIC receiving many UDP messages. User
 process can be delayed a long time at socket creation/dismantle time.

This patch prepares RCU migration, by introducing 'struct udp_table
and struct udp_hslot', and using one spinlock per chain, to reduce
contention on central rwlock.

Introducing one spinlock per chain reduces latencies, for port
randomization on heavily loaded UDP servers. This also speedup
bindings to specific ports.

udp_lib_unhash() was uninlined, becoming to big.

Some cleanups were done to ease review of following patch
(RCUification of UDP Unicast lookups)

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

1 files changed, 123 insertions, 84 deletions

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 2095abc3caba..2a6c491f97d7 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -104,12 +104,8 @@
 #include <net/xfrm.h>
 #include "udp_impl.h"
 
-/*
- *	Snmp MIB for the UDP layer
- */
-
-struct hlist_head udp_hash[UDP_HTABLE_SIZE];
-DEFINE_RWLOCK(udp_hash_lock);
+struct udp_table udp_table;
+EXPORT_SYMBOL(udp_table);
 
 int sysctl_udp_mem[3] __read_mostly;
 int sysctl_udp_rmem_min __read_mostly;
@@ -123,7 +119,7 @@ atomic_t udp_memory_allocated;
 EXPORT_SYMBOL(udp_memory_allocated);
 
 static int udp_lib_lport_inuse(struct net *net, __u16 num,
-			       const struct hlist_head udptable[],
+			       const struct udp_hslot *hslot,
 			       struct sock *sk,
 			       int (*saddr_comp)(const struct sock *sk1,
 						 const struct sock *sk2))
@@ -131,7 +127,7 @@ static int udp_lib_lport_inuse(struct net *net, __u16 num,
 	struct sock *sk2;
 	struct hlist_node *node;
 
-	sk_for_each(sk2, node, &udptable[udp_hashfn(net, num)])
+	sk_for_each(sk2, node, &hslot->head)
 		if (net_eq(sock_net(sk2), net)			&&
 		    sk2 != sk					&&
 		    sk2->sk_hash == num				&&
@@ -154,12 +150,11 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
 		       int (*saddr_comp)(const struct sock *sk1,
 					 const struct sock *sk2 )    )
 {
-	struct hlist_head *udptable = sk->sk_prot->h.udp_hash;
+	struct udp_hslot *hslot;
+	struct udp_table *udptable = sk->sk_prot->h.udp_table;
 	int    error = 1;
 	struct net *net = sock_net(sk);
 
-	write_lock_bh(&udp_hash_lock);
-
 	if (!snum) {
 		int low, high, remaining;
 		unsigned rand;
@@ -171,26 +166,34 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
 		rand = net_random();
 		snum = first = rand % remaining + low;
 		rand |= 1;
-		while (udp_lib_lport_inuse(net, snum, udptable, sk,
-					   saddr_comp)) {
+		for (;;) {
+			hslot = &udptable->hash[udp_hashfn(net, snum)];
+			spin_lock_bh(&hslot->lock);
+			if (!udp_lib_lport_inuse(net, snum, hslot, sk, saddr_comp))
+				break;
+			spin_unlock_bh(&hslot->lock);
 			do {
 				snum = snum + rand;
 			} while (snum < low || snum > high);
 			if (snum == first)
 				goto fail;
 		}
-	} else if (udp_lib_lport_inuse(net, snum, udptable, sk, saddr_comp))
-		goto fail;
-
+	} else {
+		hslot = &udptable->hash[udp_hashfn(net, snum)];
+		spin_lock_bh(&hslot->lock);
+		if (udp_lib_lport_inuse(net, snum, hslot, sk, saddr_comp))
+			goto fail_unlock;
+	}
 	inet_sk(sk)->num = snum;
 	sk->sk_hash = snum;
 	if (sk_unhashed(sk)) {
-		sk_add_node(sk, &udptable[udp_hashfn(net, snum)]);
+		sk_add_node(sk, &hslot->head);
 		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 	}
 	error = 0;
+fail_unlock:
+	spin_unlock_bh(&hslot->lock);
 fail:
-	write_unlock_bh(&udp_hash_lock);
 	return error;
 }
 
@@ -208,63 +211,73 @@ int udp_v4_get_port(struct sock *sk, unsigned short snum)
 	return udp_lib_get_port(sk, snum, ipv4_rcv_saddr_equal);
 }
 
+static inline int compute_score(struct sock *sk, struct net *net, __be32 saddr,
+			 unsigned short hnum,
+			 __be16 sport, __be32 daddr, __be16 dport, int dif)
+{
+	int score = -1;
+
+	if (net_eq(sock_net(sk), net) && sk->sk_hash == hnum &&
+			!ipv6_only_sock(sk)) {
+		struct inet_sock *inet = inet_sk(sk);
+
+		score = (sk->sk_family == PF_INET ? 1 : 0);
+		if (inet->rcv_saddr) {
+			if (inet->rcv_saddr != daddr)
+				return -1;
+			score += 2;
+		}
+		if (inet->daddr) {
+			if (inet->daddr != saddr)
+				return -1;
+			score += 2;
+		}
+		if (inet->dport) {
+			if (inet->dport != sport)
+				return -1;
+			score += 2;
+		}
+		if (sk->sk_bound_dev_if) {
+			if (sk->sk_bound_dev_if != dif)
+				return -1;
+			score += 2;
+		}
+	}
+	return score;
+}
+
 /* UDP is nearly always wildcards out the wazoo, it makes no sense to try
  * harder than this. -DaveM
  */
 static struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
 		__be16 sport, __be32 daddr, __be16 dport,
-		int dif, struct hlist_head udptable[])
+		int dif, struct udp_table *udptable)
 {
 	struct sock *sk, *result = NULL;
 	struct hlist_node *node;
 	unsigned short hnum = ntohs(dport);
-	int badness = -1;
-
-	read_lock(&udp_hash_lock);
-	sk_for_each(sk, node, &udptable[udp_hashfn(net, hnum)]) {
-		struct inet_sock *inet = inet_sk(sk);
-
-		if (net_eq(sock_net(sk), net) && sk->sk_hash == hnum &&
-				!ipv6_only_sock(sk)) {
-			int score = (sk->sk_family == PF_INET ? 1 : 0);
-			if (inet->rcv_saddr) {
-				if (inet->rcv_saddr != daddr)
-					continue;
-				score+=2;
-			}
-			if (inet->daddr) {
-				if (inet->daddr != saddr)
-					continue;
-				score+=2;
-			}
-			if (inet->dport) {
-				if (inet->dport != sport)
-					continue;
-				score+=2;
-			}
-			if (sk->sk_bound_dev_if) {
-				if (sk->sk_bound_dev_if != dif)
-					continue;
-				score+=2;
-			}
-			if (score == 9) {
-				result = sk;
-				break;
-			} else if (score > badness) {
-				result = sk;
-				badness = score;
-			}
+	unsigned int hash = udp_hashfn(net, hnum);
+	struct udp_hslot *hslot = &udptable->hash[hash];
+	int score, badness = -1;
+
+	spin_lock(&hslot->lock);
+	sk_for_each(sk, node, &hslot->head) {
+		score = compute_score(sk, net, saddr, hnum, sport,
+				      daddr, dport, dif);
+		if (score > badness) {
+			result = sk;
+			badness = score;
 		}
 	}
 	if (result)
 		sock_hold(result);
-	read_unlock(&udp_hash_lock);
+	spin_unlock(&hslot->lock);
 	return result;
 }
 
 static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
 						 __be16 sport, __be16 dport,
-						 struct hlist_head udptable[])
+						 struct udp_table *udptable)
 {
 	struct sock *sk;
 	const struct iphdr *iph = ip_hdr(skb);
@@ -280,7 +293,7 @@ static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
 struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
 			     __be32 daddr, __be16 dport, int dif)
 {
-	return __udp4_lib_lookup(net, saddr, sport, daddr, dport, dif, udp_hash);
+	return __udp4_lib_lookup(net, saddr, sport, daddr, dport, dif, &udp_table);
 }
 EXPORT_SYMBOL_GPL(udp4_lib_lookup);
 
@@ -323,7 +336,7 @@ found:
  * to find the appropriate port.
  */
 
-void __udp4_lib_err(struct sk_buff *skb, u32 info, struct hlist_head udptable[])
+void __udp4_lib_err(struct sk_buff *skb, u32 info, struct udp_table *udptable)
 {
 	struct inet_sock *inet;
 	struct iphdr *iph = (struct iphdr*)skb->data;
@@ -392,7 +405,7 @@ out:
 
 void udp_err(struct sk_buff *skb, u32 info)
 {
-	__udp4_lib_err(skb, info, udp_hash);
+	__udp4_lib_err(skb, info, &udp_table);
 }
 
 /*
@@ -933,6 +946,21 @@ int udp_disconnect(struct sock *sk, int flags)
 	return 0;
 }
 
+void udp_lib_unhash(struct sock *sk)
+{
+	struct udp_table *udptable = sk->sk_prot->h.udp_table;
+	unsigned int hash = udp_hashfn(sock_net(sk), sk->sk_hash);
+	struct udp_hslot *hslot = &udptable->hash[hash];
+
+	spin_lock(&hslot->lock);
+	if (sk_del_node_init(sk)) {
+		inet_sk(sk)->num = 0;
+		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
+	}
+	spin_unlock(&hslot->lock);
+}
+EXPORT_SYMBOL(udp_lib_unhash);
+
 static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 {
 	int is_udplite = IS_UDPLITE(sk);
@@ -1071,13 +1099,14 @@ drop:
 static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
 				    struct udphdr  *uh,
 				    __be32 saddr, __be32 daddr,
-				    struct hlist_head udptable[])
+				    struct udp_table *udptable)
 {
 	struct sock *sk;
+	struct udp_hslot *hslot = &udptable->hash[udp_hashfn(net, ntohs(uh->dest))];
 	int dif;
 
-	read_lock(&udp_hash_lock);
-	sk = sk_head(&udptable[udp_hashfn(net, ntohs(uh->dest))]);
+	spin_lock(&hslot->lock);
+	sk = sk_head(&hslot->head);
 	dif = skb->dev->ifindex;
 	sk = udp_v4_mcast_next(sk, uh->dest, daddr, uh->source, saddr, dif);
 	if (sk) {
@@ -1102,7 +1131,7 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
 		} while (sknext);
 	} else
 		kfree_skb(skb);
-	read_unlock(&udp_hash_lock);
+	spin_unlock(&hslot->lock);
 	return 0;
 }
 
@@ -1148,7 +1177,7 @@ static inline int udp4_csum_init(struct sk_buff *skb, struct udphdr *uh,
  *	All we need to do is get the socket, and then do a checksum.
  */
 
-int __udp4_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
+int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 		   int proto)
 {
 	struct sock *sk;
@@ -1246,7 +1275,7 @@ drop:
 
 int udp_rcv(struct sk_buff *skb)
 {
-	return __udp4_lib_rcv(skb, udp_hash, IPPROTO_UDP);
+	return __udp4_lib_rcv(skb, &udp_table, IPPROTO_UDP);
 }
 
 void udp_destroy_sock(struct sock *sk)
@@ -1488,7 +1517,7 @@ struct proto udp_prot = {
 	.sysctl_wmem	   = &sysctl_udp_wmem_min,
 	.sysctl_rmem	   = &sysctl_udp_rmem_min,
 	.obj_size	   = sizeof(struct udp_sock),
-	.h.udp_hash	   = udp_hash,
+	.h.udp_table	   = &udp_table,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_udp_setsockopt,
 	.compat_getsockopt = compat_udp_getsockopt,
@@ -1498,20 +1527,23 @@ struct proto udp_prot = {
 /* ------------------------------------------------------------------------ */
 #ifdef CONFIG_PROC_FS
 
-static struct sock *udp_get_first(struct seq_file *seq)
+static struct sock *udp_get_first(struct seq_file *seq, int start)
 {
 	struct sock *sk;
 	struct udp_iter_state *state = seq->private;
 	struct net *net = seq_file_net(seq);
 
-	for (state->bucket = 0; state->bucket < UDP_HTABLE_SIZE; ++state->bucket) {
+	for (state->bucket = start; state->bucket < UDP_HTABLE_SIZE; ++state->bucket) {
 		struct hlist_node *node;
-		sk_for_each(sk, node, state->hashtable + state->bucket) {
+		struct udp_hslot *hslot = &state->udp_table->hash[state->bucket];
+		spin_lock_bh(&hslot->lock);
+		sk_for_each(sk, node, &hslot->head) {
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (sk->sk_family == state->family)
 				goto found;
 		}
+		spin_unlock_bh(&hslot->lock);
 	}
 	sk = NULL;
 found:
@@ -1525,20 +1557,18 @@ static struct sock *udp_get_next(struct seq_file *seq, struct sock *sk)
 
 	do {
 		sk = sk_next(sk);
-try_again:
-		;
 	} while (sk && (!net_eq(sock_net(sk), net) || sk->sk_family != state->family));
 
-	if (!sk && ++state->bucket < UDP_HTABLE_SIZE) {
-		sk = sk_head(state->hashtable + state->bucket);
-		goto try_again;
+	if (!sk) {
+		spin_unlock(&state->udp_table->hash[state->bucket].lock);
+		return udp_get_first(seq, state->bucket + 1);
 	}
 	return sk;
 }
 
 static struct sock *udp_get_idx(struct seq_file *seq, loff_t pos)
 {
-	struct sock *sk = udp_get_first(seq);
+	struct sock *sk = udp_get_first(seq, 0);
 
 	if (sk)
 		while (pos && (sk = udp_get_next(seq, sk)) != NULL)
@@ -1547,9 +1577,7 @@ static struct sock *udp_get_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *udp_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(udp_hash_lock)
 {
-	read_lock(&udp_hash_lock);
 	return *pos ? udp_get_idx(seq, *pos-1) : SEQ_START_TOKEN;
 }
 
@@ -1567,9 +1595,11 @@ static void *udp_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void udp_seq_stop(struct seq_file *seq, void *v)
-	__releases(udp_hash_lock)
 {
-	read_unlock(&udp_hash_lock);
+	struct udp_iter_state *state = seq->private;
+
+	if (state->bucket < UDP_HTABLE_SIZE)
+		spin_unlock_bh(&state->udp_table->hash[state->bucket].lock);
 }
 
 static int udp_seq_open(struct inode *inode, struct file *file)
@@ -1585,7 +1615,7 @@ static int udp_seq_open(struct inode *inode, struct file *file)
 
 	s = ((struct seq_file *)file->private_data)->private;
 	s->family		= afinfo->family;
-	s->hashtable		= afinfo->hashtable;
+	s->udp_table		= afinfo->udp_table;
 	return err;
 }
 
@@ -1657,7 +1687,7 @@ int udp4_seq_show(struct seq_file *seq, void *v)
 static struct udp_seq_afinfo udp4_seq_afinfo = {
 	.name		= "udp",
 	.family		= AF_INET,
-	.hashtable	= udp_hash,
+	.udp_table	= &udp_table,
 	.seq_fops	= {
 		.owner	=	THIS_MODULE,
 	},
@@ -1692,10 +1722,21 @@ void udp4_proc_exit(void)
 }
 #endif /* CONFIG_PROC_FS */
 
+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);
+		spin_lock_init(&table->hash[i].lock);
+	}
+}
+
 void __init udp_init(void)
 {
 	unsigned long limit;
 
+	udp_table_init(&udp_table);
 	/* Set the pressure threshold up by the same strategy of TCP. It is a
 	 * fraction of global memory that is up to 1/2 at 256 MB, decreasing
 	 * toward zero with the amount of memory, with a floor of 128 pages.
@@ -1712,8 +1753,6 @@ void __init udp_init(void)
 }
 
 EXPORT_SYMBOL(udp_disconnect);
-EXPORT_SYMBOL(udp_hash);
-EXPORT_SYMBOL(udp_hash_lock);
 EXPORT_SYMBOL(udp_ioctl);
 EXPORT_SYMBOL(udp_prot);
 EXPORT_SYMBOL(udp_sendmsg);