[RFC PATCHv2 net-next 0/3] udp: Add 4-tuple hash for connected sockets

[RFC PATCHv2 net-next 0/3] udp: Add 4-tuple hash for connected sockets

[Philo Lu]

This RFC patchset introduces 4-tuple hash for connected udp sockets, to
make connected udp lookup faster. It is a tentative proposal and any
comment is welcome.

Patch1: Add a new counter for hslot2 named hash4_cnt, to avoid cache line
        miss when lookup.
Patch2 and 3: Implement 4-tuple hash for ipv4.

The detailed motivation is described in Patch 3.

AFAICT the patchset can be further improved by:
(a) Better interact with hash2/reuseport. Now hash4 hardly affects other
mechanisms, but maintaining sockets in both hash4 and hash2 lists seems
unnecessary.
(b) Support early demux and ipv6.

changelogs:
RFCv1 -> RFCv2:
- add a new struct for hslot2
- remove the sockopt UDP_HASH4 because it has little side effect for
  unconnected sockets
- add rehash in connect()
- re-organize the patch into 3 smaller ones
- other minor fix

RFCv1:
https://lore.kernel.org/all/20240913100941.8565-1-lulie@linux.alibaba.com/

Philo Lu (3):
  net/udp: Add a new struct for hash2 slot
  net/udp: Add 4-tuple hash list basis
  ipv4/udp: Add 4-tuple hash for connected socket

 include/linux/udp.h |   7 ++
 include/net/udp.h   |  44 ++++++++--
 net/ipv4/udp.c      | 197 ++++++++++++++++++++++++++++++++++++++------
 net/ipv6/udp.c      |  17 ++--
 4 files changed, 223 insertions(+), 42 deletions(-)

--
2.32.0.3.g01195cf9f

[RFC PATCHv2 net-next 1/3] net/udp: Add a new struct for hash2 slot

[Philo Lu]

Preparing for udp 4-tuple hash (uhash4 for short).

To implement uhash4 without cache line missing when lookup, hslot2 is
used to record the number of hashed sockets in hslot4. Thus adding a new
struct udp_hslot_main with field hash4_cnt, which is used by hash2. The
new struct is used to avoid doubling the size of udp_hslot.

Before uhash4 lookup, firstly checking hash4_cnt to see if there are
hashed sks in hslot4. Because hslot2 is always used in lookup, there is
no cache line miss.

Related helpers are updated, and use the helpers as possible.

uhash4 is implemented in following patches.

Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
---
 include/net/udp.h | 27 +++++++++++++++++++++++----
 net/ipv4/udp.c    | 44 +++++++++++++++++++++++---------------------
 net/ipv6/udp.c    | 15 ++++++---------
 3 files changed, 52 insertions(+), 34 deletions(-)

diff --git a/include/net/udp.h b/include/net/udp.h
index 61222545ab1cf..f13f7220c2f41 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -50,7 +50,7 @@ struct udp_skb_cb {
 #define UDP_SKB_CB(__skb)	((struct udp_skb_cb *)((__skb)->cb))
 
 /**
- *	struct udp_hslot - UDP hash slot
+ *	struct udp_hslot - UDP hash slot used by udp_table.hash
  *
  *	@head:	head of list of sockets
  *	@count:	number of sockets in 'head' list
@@ -60,7 +60,19 @@ struct udp_hslot {
 	struct hlist_head	head;
 	int			count;
 	spinlock_t		lock;
-} __attribute__((aligned(2 * sizeof(long))));
+} __aligned(2 * sizeof(long));
+
+/**
+ *	struct udp_hslot_main - UDP hash slot used by udp_table.hash2
+ *
+ *	@hslot:	basic hash slot
+ *	@hash4_cnt: number of sockets in hslot4 of the same (local port, local address)
+ */
+struct udp_hslot_main {
+	struct udp_hslot	hslot; /* must be the first member */
+	u32			hash4_cnt;
+} __aligned(2 * sizeof(long));
+#define UDP_HSLOT_MAIN(__hslot) ((struct udp_hslot_main *)(__hslot))
 
 /**
  *	struct udp_table - UDP table
@@ -72,7 +84,7 @@ struct udp_hslot {
  */
 struct udp_table {
 	struct udp_hslot	*hash;
-	struct udp_hslot	*hash2;
+	struct udp_hslot_main	*hash2;
 	unsigned int		mask;
 	unsigned int		log;
 };
@@ -84,6 +96,13 @@ static inline struct udp_hslot *udp_hashslot(struct udp_table *table,
 {
 	return &table->hash[udp_hashfn(net, num, table->mask)];
 }
+
+static inline struct udp_hslot_main *udp_hashslot2_main(struct udp_table *table,
+							unsigned int hash)
+{
+	return &table->hash2[hash & table->mask];
+}
+
 /*
  * For secondary hash, net_hash_mix() is performed before calling
  * udp_hashslot2(), this explains difference with udp_hashslot()
@@ -91,7 +110,7 @@ static inline struct udp_hslot *udp_hashslot(struct udp_table *table,
 static inline struct udp_hslot *udp_hashslot2(struct udp_table *table,
 					      unsigned int hash)
 {
-	return &table->hash2[hash & table->mask];
+	return (struct udp_hslot *)udp_hashslot2_main(table, hash);
 }
 
 extern struct proto udp_prot;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 8accbf4cb2956..e17c8ae121f27 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -486,13 +486,12 @@ struct sock *__udp4_lib_lookup(const struct net *net, __be32 saddr,
 		int sdif, struct udp_table *udptable, struct sk_buff *skb)
 {
 	unsigned short hnum = ntohs(dport);
-	unsigned int hash2, slot2;
 	struct udp_hslot *hslot2;
 	struct sock *result, *sk;
+	unsigned int hash2;
 
 	hash2 = ipv4_portaddr_hash(net, daddr, hnum);
-	slot2 = hash2 & udptable->mask;
-	hslot2 = &udptable->hash2[slot2];
+	hslot2 = udp_hashslot2(udptable, hash2);
 
 	/* Lookup connected or non-wildcard socket */
 	result = udp4_lib_lookup2(net, saddr, sport,
@@ -519,8 +518,7 @@ struct sock *__udp4_lib_lookup(const struct net *net, __be32 saddr,
 
 	/* Lookup wildcard sockets */
 	hash2 = ipv4_portaddr_hash(net, htonl(INADDR_ANY), hnum);
-	slot2 = hash2 & udptable->mask;
-	hslot2 = &udptable->hash2[slot2];
+	hslot2 = udp_hashslot2(udptable, hash2);
 
 	result = udp4_lib_lookup2(net, saddr, sport,
 				  htonl(INADDR_ANY), hnum, dif, sdif,
@@ -2266,7 +2264,7 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
 			    udptable->mask;
 		hash2 = ipv4_portaddr_hash(net, daddr, hnum) & udptable->mask;
 start_lookup:
-		hslot = &udptable->hash2[hash2];
+		hslot = &udptable->hash2[hash2].hslot;
 		offset = offsetof(typeof(*sk), __sk_common.skc_portaddr_node);
 	}
 
@@ -2537,14 +2535,13 @@ static struct sock *__udp4_lib_demux_lookup(struct net *net,
 	struct udp_table *udptable = net->ipv4.udp_table;
 	INET_ADDR_COOKIE(acookie, rmt_addr, loc_addr);
 	unsigned short hnum = ntohs(loc_port);
-	unsigned int hash2, slot2;
 	struct udp_hslot *hslot2;
+	unsigned int hash2;
 	__portpair ports;
 	struct sock *sk;
 
 	hash2 = ipv4_portaddr_hash(net, loc_addr, hnum);
-	slot2 = hash2 & udptable->mask;
-	hslot2 = &udptable->hash2[slot2];
+	hslot2 = udp_hashslot2(udptable, hash2);
 	ports = INET_COMBINED_PORTS(rmt_port, hnum);
 
 	udp_portaddr_for_each_entry_rcu(sk, &hslot2->head) {
@@ -3185,7 +3182,7 @@ static struct sock *bpf_iter_udp_batch(struct seq_file *seq)
 	batch_sks = 0;
 
 	for (; state->bucket <= udptable->mask; state->bucket++) {
-		struct udp_hslot *hslot2 = &udptable->hash2[state->bucket];
+		struct udp_hslot *hslot2 = &udptable->hash2[state->bucket].hslot;
 
 		if (hlist_empty(&hslot2->head))
 			continue;
@@ -3426,10 +3423,11 @@ __setup("uhash_entries=", set_uhash_entries);
 
 void __init udp_table_init(struct udp_table *table, const char *name)
 {
-	unsigned int i;
+	unsigned int i, slot_size;
 
+	slot_size = sizeof(struct udp_hslot) + sizeof(struct udp_hslot_main);
 	table->hash = alloc_large_system_hash(name,
-					      2 * sizeof(struct udp_hslot),
+					      slot_size,
 					      uhash_entries,
 					      21, /* one slot per 2 MB */
 					      0,
@@ -3438,16 +3436,17 @@ void __init udp_table_init(struct udp_table *table, const char *name)
 					      UDP_HTABLE_SIZE_MIN,
 					      UDP_HTABLE_SIZE_MAX);
 
-	table->hash2 = table->hash + (table->mask + 1);
+	table->hash2 = UDP_HSLOT_MAIN(table->hash + (table->mask + 1));
 	for (i = 0; i <= table->mask; i++) {
 		INIT_HLIST_HEAD(&table->hash[i].head);
 		table->hash[i].count = 0;
 		spin_lock_init(&table->hash[i].lock);
 	}
 	for (i = 0; i <= table->mask; i++) {
-		INIT_HLIST_HEAD(&table->hash2[i].head);
-		table->hash2[i].count = 0;
-		spin_lock_init(&table->hash2[i].lock);
+		INIT_HLIST_HEAD(&table->hash2[i].hslot.head);
+		table->hash2[i].hslot.count = 0;
+		spin_lock_init(&table->hash2[i].hslot.lock);
+		table->hash2[i].hash4_cnt = 0;
 	}
 }
 
@@ -3474,18 +3473,20 @@ static void __net_init udp_sysctl_init(struct net *net)
 static struct udp_table __net_init *udp_pernet_table_alloc(unsigned int hash_entries)
 {
 	struct udp_table *udptable;
+	unsigned int slot_size;
 	int i;
 
 	udptable = kmalloc(sizeof(*udptable), GFP_KERNEL);
 	if (!udptable)
 		goto out;
 
-	udptable->hash = vmalloc_huge(hash_entries * 2 * sizeof(struct udp_hslot),
+	slot_size = sizeof(struct udp_hslot) + sizeof(struct udp_hslot_main);
+	udptable->hash = vmalloc_huge(hash_entries * slot_size,
 				      GFP_KERNEL_ACCOUNT);
 	if (!udptable->hash)
 		goto free_table;
 
-	udptable->hash2 = udptable->hash + hash_entries;
+	udptable->hash2 = UDP_HSLOT_MAIN(udptable->hash + hash_entries);
 	udptable->mask = hash_entries - 1;
 	udptable->log = ilog2(hash_entries);
 
@@ -3494,9 +3495,10 @@ static struct udp_table __net_init *udp_pernet_table_alloc(unsigned int hash_ent
 		udptable->hash[i].count = 0;
 		spin_lock_init(&udptable->hash[i].lock);
 
-		INIT_HLIST_HEAD(&udptable->hash2[i].head);
-		udptable->hash2[i].count = 0;
-		spin_lock_init(&udptable->hash2[i].lock);
+		INIT_HLIST_HEAD(&udptable->hash2[i].hslot.head);
+		udptable->hash2[i].hslot.count = 0;
+		spin_lock_init(&udptable->hash2[i].hslot.lock);
+		udptable->hash2[i].hash4_cnt = 0;
 	}
 
 	return udptable;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 52dfbb2ff1a80..bbf3352213c40 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -224,13 +224,12 @@ struct sock *__udp6_lib_lookup(const struct net *net,
 			       struct sk_buff *skb)
 {
 	unsigned short hnum = ntohs(dport);
-	unsigned int hash2, slot2;
 	struct udp_hslot *hslot2;
 	struct sock *result, *sk;
+	unsigned int hash2;
 
 	hash2 = ipv6_portaddr_hash(net, daddr, hnum);
-	slot2 = hash2 & udptable->mask;
-	hslot2 = &udptable->hash2[slot2];
+	hslot2 = udp_hashslot2(udptable, hash2);
 
 	/* Lookup connected or non-wildcard sockets */
 	result = udp6_lib_lookup2(net, saddr, sport,
@@ -257,8 +256,7 @@ struct sock *__udp6_lib_lookup(const struct net *net,
 
 	/* Lookup wildcard sockets */
 	hash2 = ipv6_portaddr_hash(net, &in6addr_any, hnum);
-	slot2 = hash2 & udptable->mask;
-	hslot2 = &udptable->hash2[slot2];
+	hslot2 = udp_hashslot2(udptable, hash2);
 
 	result = udp6_lib_lookup2(net, saddr, sport,
 				  &in6addr_any, hnum, dif, sdif,
@@ -859,7 +857,7 @@ static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
 			    udptable->mask;
 		hash2 = ipv6_portaddr_hash(net, daddr, hnum) & udptable->mask;
 start_lookup:
-		hslot = &udptable->hash2[hash2];
+		hslot = &udptable->hash2[hash2].hslot;
 		offset = offsetof(typeof(*sk), __sk_common.skc_portaddr_node);
 	}
 
@@ -1065,14 +1063,13 @@ static struct sock *__udp6_lib_demux_lookup(struct net *net,
 {
 	struct udp_table *udptable = net->ipv4.udp_table;
 	unsigned short hnum = ntohs(loc_port);
-	unsigned int hash2, slot2;
 	struct udp_hslot *hslot2;
+	unsigned int hash2;
 	__portpair ports;
 	struct sock *sk;
 
 	hash2 = ipv6_portaddr_hash(net, loc_addr, hnum);
-	slot2 = hash2 & udptable->mask;
-	hslot2 = &udptable->hash2[slot2];
+	hslot2 = udp_hashslot2(udptable, hash2);
 	ports = INET_COMBINED_PORTS(rmt_port, hnum);
 
 	udp_portaddr_for_each_entry_rcu(sk, &hslot2->head) {
-- 
2.32.0.3.g01195cf9f

[RFC PATCHv2 net-next 1/3] net/udp: Add a new struct for hash2 slot

[Gur Stavi]

> + *	@hslot:	basic hash slot
> + *	@hash4_cnt: number of sockets in hslot4 of the same (local port, local address)
> + */
> +struct udp_hslot_main {
> +	struct udp_hslot	hslot; /* must be the first member */
> +	u32			hash4_cnt;
> +} __aligned(2 * sizeof(long));
> +#define UDP_HSLOT_MAIN(__hslot) ((struct udp_hslot_main *)(__hslot))

Wouldn't container_of be more suitable than brutal cast?

> @@ -91,7 +110,7 @@ static inline struct udp_hslot *udp_hashslot(struct udp_table *table,
>  static inline struct udp_hslot *udp_hashslot2(struct udp_table *table,
>  					      unsigned int hash)
>  {
> -	return &table->hash2[hash & table->mask];
> +	return (struct udp_hslot *)udp_hashslot2_main(table, hash);

Why cast and not use ->hslot. Preferably with a local variable?

> @@ -3438,16 +3436,17 @@ void __init udp_table_init(struct udp_table *table, const char *name)
>  					      UDP_HTABLE_SIZE_MIN,
>  					      UDP_HTABLE_SIZE_MAX);
>
> -	table->hash2 = table->hash + (table->mask + 1);
> +	table->hash2 = UDP_HSLOT_MAIN(table->hash + (table->mask + 1));

Wouldn't it be simpler to just cast to void? It is pure pointer
arithmetic where type checking is meaningless.
(void *)(table->hash + (table->mask + 1))
I realize now why UDP_HSLOT_MAIN couldn't use container_of but it
just demonstrates how convoluted this is.

Re: [RFC PATCHv2 net-next 1/3] net/udp: Add a new struct for hash2 slot

[Philo Lu]

On 2024/9/24 20:30, Gur Stavi wrote:
>> + *	@hslot:	basic hash slot
>> + *	@hash4_cnt: number of sockets in hslot4 of the same (local port, local address)
>> + */
>> +struct udp_hslot_main {
>> +	struct udp_hslot	hslot; /* must be the first member */
>> +	u32			hash4_cnt;
>> +} __aligned(2 * sizeof(long));
>> +#define UDP_HSLOT_MAIN(__hslot) ((struct udp_hslot_main *)(__hslot))
> 
> Wouldn't container_of be more suitable than brutal cast?

I think struct udp_hslot_main is like a subclass of struct udp_hslot, so 
casting is reasonable here.

> 
>> @@ -91,7 +110,7 @@ static inline struct udp_hslot *udp_hashslot(struct udp_table *table,
>>   static inline struct udp_hslot *udp_hashslot2(struct udp_table *table,
>>   					      unsigned int hash)
>>   {
>> -	return &table->hash2[hash & table->mask];
>> +	return (struct udp_hslot *)udp_hashslot2_main(table, hash);
> 
> Why cast and not use ->hslot. Preferably with a local variable?

Got it. Will fix.

> 
>> @@ -3438,16 +3436,17 @@ void __init udp_table_init(struct udp_table *table, const char *name)
>>   					      UDP_HTABLE_SIZE_MIN,
>>   					      UDP_HTABLE_SIZE_MAX);
>>
>> -	table->hash2 = table->hash + (table->mask + 1);
>> +	table->hash2 = UDP_HSLOT_MAIN(table->hash + (table->mask + 1));
> 
> Wouldn't it be simpler to just cast to void? It is pure pointer
> arithmetic where type checking is meaningless.
> (void *)(table->hash + (table->mask + 1))
> I realize now why UDP_HSLOT_MAIN couldn't use container_of but it
> just demonstrates how convoluted this is.

Will fix. I agree that (void *) is better here.

Thank you for your review, Gur.

-- 
Philo

[RFC PATCHv2 net-next 1/3] net/udp: Add a new struct for hash2 slot

[Gur Stavi]

> @@ -224,13 +224,12 @@ struct sock *__udp6_lib_lookup(const struct net *net,
>  			       struct sk_buff *skb)
>  {
>  	unsigned short hnum = ntohs(dport);
> -	unsigned int hash2, slot2;
>  	struct udp_hslot *hslot2;
>  	struct sock *result, *sk;
> +	unsigned int hash2;
>
>  	hash2 = ipv6_portaddr_hash(net, daddr, hnum);
> -	slot2 = hash2 & udptable->mask;
> -	hslot2 = &udptable->hash2[slot2];
> +	hslot2 = udp_hashslot2(udptable, hash2);
>

Why not minimize the code change by using udptable->hash2[slot2].hslot?
Especially since later you do it in __udp6_lib_mcast_deliver.
I think that many developers would find usage of C primitives more
readable.

Re: [RFC PATCHv2 net-next 1/3] net/udp: Add a new struct for hash2 slot

[Philo Lu]

On 2024/9/24 20:51, Gur Stavi wrote:
>> @@ -224,13 +224,12 @@ struct sock *__udp6_lib_lookup(const struct net *net,
>>   			       struct sk_buff *skb)
>>   {
>>   	unsigned short hnum = ntohs(dport);
>> -	unsigned int hash2, slot2;
>>   	struct udp_hslot *hslot2;
>>   	struct sock *result, *sk;
>> +	unsigned int hash2;
>>
>>   	hash2 = ipv6_portaddr_hash(net, daddr, hnum);
>> -	slot2 = hash2 & udptable->mask;
>> -	hslot2 = &udptable->hash2[slot2];
>> +	hslot2 = udp_hashslot2(udptable, hash2);
>>
> 
> Why not minimize the code change by using udptable->hash2[slot2].hslot?
> Especially since later you do it in __udp6_lib_mcast_deliver.
> I think that many developers would find usage of C primitives more
> readable.

Yes I can use udptable->hash2[slot2].hslot. But I prefer the 
udp_hashslot2() helper, because I found I have to add ".hslot" at many 
places, while most of them look exactly what udp_hashslot2() does. I 
think replacing them may get the codes simpler and benefit future coding.

Some places like __udp6_lib_mcast_deliver() get hslot2 differently from 
udp_hashslot2(), so just appending ".hslot" to avoid functionality change.

Thanks.
-- 
Philo

[RFC PATCHv2 net-next 2/3] net/udp: Add 4-tuple hash list basis

[Philo Lu]

Add a new hash list, hash4, in udp table. It will be used to implement
4-tuple hash for connected udp sockets. This patch adds the hlist to
table, and implements helpers and the initialization. 4-tuple hash is
implemented in the following patch.

Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
Signed-off-by: Cambda Zhu <cambda@linux.alibaba.com>
Signed-off-by: Fred Chen <fred.cc@alibaba-inc.com>
Signed-off-by: Yubing Qiu <yubing.qiuyubing@alibaba-inc.com>
---
 include/linux/udp.h |  7 +++++++
 include/net/udp.h   | 16 +++++++++++++++-
 net/ipv4/udp.c      | 17 +++++++++++++----
 3 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/include/linux/udp.h b/include/linux/udp.h
index 3eb3f2b9a2a05..c04808360a05d 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -56,6 +56,10 @@ struct udp_sock {
 	int		 pending;	/* Any pending frames ? */
 	__u8		 encap_type;	/* Is this an Encapsulation socket? */
 
+	/* For UDP 4-tuple hash */
+	__u16 udp_lrpa_hash;
+	struct hlist_node udp_lrpa_node;
+
 	/*
 	 * Following member retains the information to create a UDP header
 	 * when the socket is uncorked.
@@ -206,6 +210,9 @@ static inline void udp_allow_gso(struct sock *sk)
 #define udp_portaddr_for_each_entry_rcu(__sk, list) \
 	hlist_for_each_entry_rcu(__sk, list, __sk_common.skc_portaddr_node)
 
+#define udp_lrpa_for_each_entry_rcu(__up, list) \
+	hlist_for_each_entry_rcu(__up, list, udp_lrpa_node)
+
 #define IS_UDPLITE(__sk) (__sk->sk_protocol == IPPROTO_UDPLITE)
 
 #endif	/* _LINUX_UDP_H */
diff --git a/include/net/udp.h b/include/net/udp.h
index f13f7220c2f41..94005363b8abd 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -50,7 +50,7 @@ struct udp_skb_cb {
 #define UDP_SKB_CB(__skb)	((struct udp_skb_cb *)((__skb)->cb))
 
 /**
- *	struct udp_hslot - UDP hash slot used by udp_table.hash
+ *	struct udp_hslot - UDP hash slot used by udp_table.hash/hash4
  *
  *	@head:	head of list of sockets
  *	@count:	number of sockets in 'head' list
@@ -79,12 +79,15 @@ struct udp_hslot_main {
  *
  *	@hash:	hash table, sockets are hashed on (local port)
  *	@hash2:	hash table, sockets are hashed on (local port, local address)
+ *	@hash4:	hash table, connected sockets are hashed on
+ *		(local port, local address, remote port, remote address)
  *	@mask:	number of slots in hash tables, minus 1
  *	@log:	log2(number of slots in hash table)
  */
 struct udp_table {
 	struct udp_hslot	*hash;
 	struct udp_hslot_main	*hash2;
+	struct udp_hslot	*hash4;
 	unsigned int		mask;
 	unsigned int		log;
 };
@@ -113,6 +116,17 @@ static inline struct udp_hslot *udp_hashslot2(struct udp_table *table,
 	return (struct udp_hslot *)udp_hashslot2_main(table, hash);
 }
 
+static inline struct udp_hslot *udp_hashslot4(struct udp_table *table,
+					      unsigned int hash)
+{
+	return &table->hash4[hash & table->mask];
+}
+
+static inline bool udp_hashed4(const struct sock *sk)
+{
+	return !hlist_unhashed(&udp_sk(sk)->udp_lrpa_node);
+}
+
 extern struct proto udp_prot;
 
 extern atomic_long_t udp_memory_allocated;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index e17c8ae121f27..5564896686fa5 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -3425,7 +3425,7 @@ void __init udp_table_init(struct udp_table *table, const char *name)
 {
 	unsigned int i, slot_size;
 
-	slot_size = sizeof(struct udp_hslot) + sizeof(struct udp_hslot_main);
+	slot_size = 2 * sizeof(struct udp_hslot) + sizeof(struct udp_hslot_main);
 	table->hash = alloc_large_system_hash(name,
 					      slot_size,
 					      uhash_entries,
@@ -3437,6 +3437,7 @@ void __init udp_table_init(struct udp_table *table, const char *name)
 					      UDP_HTABLE_SIZE_MAX);
 
 	table->hash2 = UDP_HSLOT_MAIN(table->hash + (table->mask + 1));
+	table->hash4 = (struct udp_hslot *)(table->hash2 + (table->mask + 1));
 	for (i = 0; i <= table->mask; i++) {
 		INIT_HLIST_HEAD(&table->hash[i].head);
 		table->hash[i].count = 0;
@@ -3448,6 +3449,11 @@ void __init udp_table_init(struct udp_table *table, const char *name)
 		spin_lock_init(&table->hash2[i].hslot.lock);
 		table->hash2[i].hash4_cnt = 0;
 	}
+	for (i = 0; i <= table->mask; i++) {
+		INIT_HLIST_HEAD(&table->hash4[i].head);
+		table->hash4[i].count = 0;
+		spin_lock_init(&table->hash4[i].lock);
+	}
 }
 
 u32 udp_flow_hashrnd(void)
@@ -3480,16 +3486,15 @@ static struct udp_table __net_init *udp_pernet_table_alloc(unsigned int hash_ent
 	if (!udptable)
 		goto out;
 
-	slot_size = sizeof(struct udp_hslot) + sizeof(struct udp_hslot_main);
+	slot_size = 2 * sizeof(struct udp_hslot) + sizeof(struct udp_hslot_main);
 	udptable->hash = vmalloc_huge(hash_entries * slot_size,
 				      GFP_KERNEL_ACCOUNT);
 	if (!udptable->hash)
 		goto free_table;
 
 	udptable->hash2 = UDP_HSLOT_MAIN(udptable->hash + hash_entries);
-	udptable->mask = hash_entries - 1;
+	udptable->hash4 = (struct udp_hslot *)(udptable->hash2 + hash_entries);
 	udptable->log = ilog2(hash_entries);
-
 	for (i = 0; i < hash_entries; i++) {
 		INIT_HLIST_HEAD(&udptable->hash[i].head);
 		udptable->hash[i].count = 0;
@@ -3499,6 +3504,10 @@ static struct udp_table __net_init *udp_pernet_table_alloc(unsigned int hash_ent
 		udptable->hash2[i].hslot.count = 0;
 		spin_lock_init(&udptable->hash2[i].hslot.lock);
 		udptable->hash2[i].hash4_cnt = 0;
+
+		INIT_HLIST_HEAD(&udptable->hash4[i].head);
+		udptable->hash4[i].count = 0;
+		spin_lock_init(&udptable->hash4[i].lock);
 	}
 
 	return udptable;
-- 
2.32.0.3.g01195cf9f

[RFC PATCHv2 net-next 3/3] ipv4/udp: Add 4-tuple hash for connected socket

[Philo Lu]

Currently, the udp_table has two hash table, the port hash and portaddr
hash. Usually for UDP servers, all sockets have the same local port and
addr, so they are all on the same hash slot within a reuseport group.

In some applications, UDP servers use connect() to manage clients. In
particular, when firstly receiving from an unseen 4 tuple, a new socket
is created and connect()ed to the remote addr:port, and then the fd is
used exclusively by the client.

Once there are connected sks in a reuseport group, udp has to score all
sks in the same hash2 slot to find the best match. This could be
inefficient with a large number of connections, resulting in high
softirq overhead.

To solve the problem, this patch implement 4-tuple hash for connected
udp sockets. During connect(), hash4 slot is updated, as well as a
corresponding counter, hash4_cnt, in hslot2. In __udp4_lib_lookup(),
hslot4 will be searched firstly if the counter is non-zero. Otherwise,
hslot2 is used like before. Note that only connected sockets enter this
hash4 path, while un-connected ones are not affected.

Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
Signed-off-by: Cambda Zhu <cambda@linux.alibaba.com>
Signed-off-by: Fred Chen <fred.cc@alibaba-inc.com>
Signed-off-by: Yubing Qiu <yubing.qiuyubing@alibaba-inc.com>
---
 include/net/udp.h |   3 +-
 net/ipv4/udp.c    | 140 ++++++++++++++++++++++++++++++++++++++++++++--
 net/ipv6/udp.c    |   2 +-
 3 files changed, 139 insertions(+), 6 deletions(-)

diff --git a/include/net/udp.h b/include/net/udp.h
index 94005363b8abd..3bb0c4f24692a 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -226,7 +226,7 @@ static inline int udp_lib_hash(struct sock *sk)
 }
 
 void udp_lib_unhash(struct sock *sk);
-void udp_lib_rehash(struct sock *sk, u16 new_hash);
+void udp_lib_rehash(struct sock *sk, u16 new_hash, u16 new_hash4);
 
 static inline void udp_lib_close(struct sock *sk, long timeout)
 {
@@ -319,6 +319,7 @@ int udp_rcv(struct sk_buff *skb);
 int udp_ioctl(struct sock *sk, int cmd, int *karg);
 int udp_init_sock(struct sock *sk);
 int udp_pre_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
+int udp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
 int __udp_disconnect(struct sock *sk, int flags);
 int udp_disconnect(struct sock *sk, int flags);
 __poll_t udp_poll(struct file *file, struct socket *sock, poll_table *wait);
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 5564896686fa5..1d48d3ad17c57 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -478,6 +478,27 @@ static struct sock *udp4_lib_lookup2(const struct net *net,
 	return result;
 }
 
+static struct sock *udp4_lib_lookup4(const struct net *net,
+				     __be32 saddr, __be16 sport,
+				     __be32 daddr, unsigned int hnum,
+				     int dif, int sdif,
+				     struct udp_table *udptable)
+{
+	unsigned int hash4 = udp_ehashfn(net, daddr, hnum, saddr, sport);
+	const __portpair ports = INET_COMBINED_PORTS(sport, hnum);
+	struct udp_hslot *hslot4 = udp_hashslot4(udptable, hash4);
+	struct udp_sock *up;
+	struct sock *sk;
+
+	INET_ADDR_COOKIE(acookie, saddr, daddr);
+	udp_lrpa_for_each_entry_rcu(up, &hslot4->head) {
+		sk = (struct sock *)up;
+		if (inet_match(net, sk, acookie, ports, dif, sdif))
+			return sk;
+	}
+	return NULL;
+}
+
 /* UDP is nearly always wildcards out the wazoo, it makes no sense to try
  * harder than this. -DaveM
  */
@@ -493,6 +514,12 @@ struct sock *__udp4_lib_lookup(const struct net *net, __be32 saddr,
 	hash2 = ipv4_portaddr_hash(net, daddr, hnum);
 	hslot2 = udp_hashslot2(udptable, hash2);
 
+	if (UDP_HSLOT_MAIN(hslot2)->hash4_cnt) {
+		result = udp4_lib_lookup4(net, saddr, sport, daddr, hnum, dif, sdif, udptable);
+		if (result) /* udp4_lib_lookup4 return sk or NULL */
+			return result;
+	}
+
 	/* Lookup connected or non-wildcard socket */
 	result = udp4_lib_lookup2(net, saddr, sport,
 				  daddr, hnum, dif, sdif,
@@ -1931,6 +1958,83 @@ int udp_pre_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 }
 EXPORT_SYMBOL(udp_pre_connect);
 
+/* In hash4, rehash can also happen in connect(), where hash4_cnt keeps unchanged. */
+static void udp4_rehash4(struct udp_table *udptable, struct sock *sk, u16 newhash4)
+{
+	struct udp_hslot *hslot4, *nhslot4;
+
+	hslot4 = udp_hashslot4(udptable, udp_sk(sk)->udp_lrpa_hash);
+	nhslot4 = udp_hashslot4(udptable, newhash4);
+	udp_sk(sk)->udp_lrpa_hash = newhash4;
+
+	if (hslot4 != nhslot4) {
+		spin_lock_bh(&hslot4->lock);
+		hlist_del_init_rcu(&udp_sk(sk)->udp_lrpa_node);
+		hslot4->count--;
+		spin_unlock_bh(&hslot4->lock);
+
+		spin_lock_bh(&nhslot4->lock);
+		hlist_add_head_rcu(&udp_sk(sk)->udp_lrpa_node, &nhslot4->head);
+		nhslot4->count++;
+		spin_unlock_bh(&nhslot4->lock);
+	}
+}
+
+/* call with sock lock */
+static void udp4_hash4(struct sock *sk)
+{
+	struct udp_hslot *hslot, *hslot4;
+	struct udp_hslot_main *hslotm2;
+	struct net *net = sock_net(sk);
+	struct udp_table *udptable;
+	unsigned int hash;
+
+	if (sk_unhashed(sk) || inet_sk(sk)->inet_rcv_saddr == htonl(INADDR_ANY))
+		return;
+
+	hash = udp_ehashfn(net, inet_sk(sk)->inet_rcv_saddr, inet_sk(sk)->inet_num,
+			   inet_sk(sk)->inet_daddr, inet_sk(sk)->inet_dport);
+
+	udptable = net->ipv4.udp_table;
+	if (udp_hashed4(sk)) {
+		udp4_rehash4(udptable, sk, hash);
+		return;
+	}
+
+	hslot = udp_hashslot(udptable, net, udp_sk(sk)->udp_port_hash);
+	hslotm2 = udp_hashslot2_main(udptable, udp_sk(sk)->udp_portaddr_hash);
+	hslot4 = udp_hashslot4(udptable, hash);
+	udp_sk(sk)->udp_lrpa_hash = hash;
+
+	spin_lock_bh(&hslot->lock);
+	if (rcu_access_pointer(sk->sk_reuseport_cb))
+		reuseport_detach_sock(sk);
+
+	spin_lock(&hslot4->lock);
+	hlist_add_head_rcu(&udp_sk(sk)->udp_lrpa_node, &hslot4->head);
+	hslot4->count++;
+	spin_unlock(&hslot4->lock);
+
+	spin_lock(&hslotm2->hslot.lock);
+	hslotm2->hash4_cnt++;
+	spin_unlock(&hslotm2->hslot.lock);
+
+	spin_unlock_bh(&hslot->lock);
+}
+
+int udp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
+{
+	int res;
+
+	lock_sock(sk);
+	res = __ip4_datagram_connect(sk, uaddr, addr_len);
+	if (!res)
+		udp4_hash4(sk);
+	release_sock(sk);
+	return res;
+}
+EXPORT_SYMBOL(udp_connect);
+
 int __udp_disconnect(struct sock *sk, int flags)
 {
 	struct inet_sock *inet = inet_sk(sk);
@@ -1972,7 +2076,7 @@ void udp_lib_unhash(struct sock *sk)
 {
 	if (sk_hashed(sk)) {
 		struct udp_table *udptable = udp_get_table_prot(sk);
-		struct udp_hslot *hslot, *hslot2;
+		struct udp_hslot *hslot, *hslot2, *hslot4;
 
 		hslot  = udp_hashslot(udptable, sock_net(sk),
 				      udp_sk(sk)->udp_port_hash);
@@ -1990,6 +2094,18 @@ void udp_lib_unhash(struct sock *sk)
 			hlist_del_init_rcu(&udp_sk(sk)->udp_portaddr_node);
 			hslot2->count--;
 			spin_unlock(&hslot2->lock);
+
+			if (udp_hashed4(sk)) {
+				hslot4 = udp_hashslot4(udptable, udp_sk(sk)->udp_lrpa_hash);
+				spin_lock(&hslot4->lock);
+				hlist_del_init_rcu(&udp_sk(sk)->udp_lrpa_node);
+				hslot4->count--;
+				spin_unlock(&hslot4->lock);
+
+				spin_lock(&hslot2->lock);
+				UDP_HSLOT_MAIN(hslot2)->hash4_cnt--;
+				spin_unlock(&hslot2->lock);
+			}
 		}
 		spin_unlock_bh(&hslot->lock);
 	}
@@ -1999,7 +2115,7 @@ EXPORT_SYMBOL(udp_lib_unhash);
 /*
  * inet_rcv_saddr was changed, we must rehash secondary hash
  */
-void udp_lib_rehash(struct sock *sk, u16 newhash)
+void udp_lib_rehash(struct sock *sk, u16 newhash, u16 newhash4)
 {
 	if (sk_hashed(sk)) {
 		struct udp_table *udptable = udp_get_table_prot(sk);
@@ -2031,6 +2147,19 @@ void udp_lib_rehash(struct sock *sk, u16 newhash)
 				spin_unlock(&nhslot2->lock);
 			}
 
+			if (udp_hashed4(sk)) {
+				udp4_rehash4(udptable, sk, newhash4);
+
+				if (hslot2 != nhslot2) {
+					spin_lock(&hslot2->lock);
+					UDP_HSLOT_MAIN(hslot2)->hash4_cnt--;
+					spin_unlock(&hslot2->lock);
+
+					spin_lock(&nhslot2->lock);
+					UDP_HSLOT_MAIN(nhslot2)->hash4_cnt++;
+					spin_unlock(&nhslot2->lock);
+				}
+			}
 			spin_unlock_bh(&hslot->lock);
 		}
 	}
@@ -2042,7 +2171,10 @@ void udp_v4_rehash(struct sock *sk)
 	u16 new_hash = ipv4_portaddr_hash(sock_net(sk),
 					  inet_sk(sk)->inet_rcv_saddr,
 					  inet_sk(sk)->inet_num);
-	udp_lib_rehash(sk, new_hash);
+	u16 new_hash4 = udp_ehashfn(sock_net(sk),
+				    inet_sk(sk)->inet_rcv_saddr, inet_sk(sk)->inet_num,
+				    inet_sk(sk)->inet_daddr, inet_sk(sk)->inet_dport);
+	udp_lib_rehash(sk, new_hash, new_hash4);
 }
 
 static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
@@ -2935,7 +3067,7 @@ struct proto udp_prot = {
 	.owner			= THIS_MODULE,
 	.close			= udp_lib_close,
 	.pre_connect		= udp_pre_connect,
-	.connect		= ip4_datagram_connect,
+	.connect		= udp_connect,
 	.disconnect		= udp_disconnect,
 	.ioctl			= udp_ioctl,
 	.init			= udp_init_sock,
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index bbf3352213c40..4d3dfcb48a39d 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -111,7 +111,7 @@ void udp_v6_rehash(struct sock *sk)
 					  &sk->sk_v6_rcv_saddr,
 					  inet_sk(sk)->inet_num);
 
-	udp_lib_rehash(sk, new_hash);
+	udp_lib_rehash(sk, new_hash, 0); /* 4-tuple hash not implemented */
 }
 
 static int compute_score(struct sock *sk, const struct net *net,
-- 
2.32.0.3.g01195cf9f

[RFC PATCHv2 net-next 3/3] ipv4/udp: Add 4-tuple hash for connected socket

[Gur Stavi]

> +/* In hash4, rehash can also happen in connect(), where hash4_cnt keeps unchanged. */
> +static void udp4_rehash4(struct udp_table *udptable, struct sock *sk, u16 newhash4)
> +{
> +	struct udp_hslot *hslot4, *nhslot4;
> +
> +	hslot4 = udp_hashslot4(udptable, udp_sk(sk)->udp_lrpa_hash);
> +	nhslot4 = udp_hashslot4(udptable, newhash4);
> +	udp_sk(sk)->udp_lrpa_hash = newhash4;
> +
> +	if (hslot4 != nhslot4) {
> +		spin_lock_bh(&hslot4->lock);
> +		hlist_del_init_rcu(&udp_sk(sk)->udp_lrpa_node);
> +		hslot4->count--;
> +		spin_unlock_bh(&hslot4->lock);

I realize this is copied from udp_lib_rehash, but isn't it an RCU bug?
Once a node is removed from a list, shouldn't synchronize_rcu be called
before it is reused for a new list? A reader that was traversing the
old list may find itself on the new list.

> +
> +		spin_lock_bh(&nhslot4->lock);
> +		hlist_add_head_rcu(&udp_sk(sk)->udp_lrpa_node, &nhslot4->head);
> +		nhslot4->count++;
> +		spin_unlock_bh(&nhslot4->lock);
> +	}
> +}
> +

Re: [RFC PATCHv2 net-next 3/3] ipv4/udp: Add 4-tuple hash for connected socket

[Philo Lu]

On 2024/9/24 20:31, Gur Stavi wrote:
>> +/* In hash4, rehash can also happen in connect(), where hash4_cnt keeps unchanged. */
>> +static void udp4_rehash4(struct udp_table *udptable, struct sock *sk, u16 newhash4)
>> +{
>> +	struct udp_hslot *hslot4, *nhslot4;
>> +
>> +	hslot4 = udp_hashslot4(udptable, udp_sk(sk)->udp_lrpa_hash);
>> +	nhslot4 = udp_hashslot4(udptable, newhash4);
>> +	udp_sk(sk)->udp_lrpa_hash = newhash4;
>> +
>> +	if (hslot4 != nhslot4) {
>> +		spin_lock_bh(&hslot4->lock);
>> +		hlist_del_init_rcu(&udp_sk(sk)->udp_lrpa_node);
>> +		hslot4->count--;
>> +		spin_unlock_bh(&hslot4->lock);
> 
> I realize this is copied from udp_lib_rehash, but isn't it an RCU bug?
> Once a node is removed from a list, shouldn't synchronize_rcu be called
> before it is reused for a new list? A reader that was traversing the
> old list may find itself on the new list.
> 
>> +
>> +		spin_lock_bh(&nhslot4->lock);
>> +		hlist_add_head_rcu(&udp_sk(sk)->udp_lrpa_node, &nhslot4->head);
>> +		nhslot4->count++;
>> +		spin_unlock_bh(&nhslot4->lock);
>> +	}
>> +}
>> +

Good catch! IIUC, synchronize_rcu() is needed here, or otherwise, this 
could happen:

    Reader(lookup)     Writer(rehash)
    -----------------  ---------------
1. rcu_read_lock()
2. pos = sk;
3.                     hlist_del_init_rcu(sk, old_slot)
4.                     hlist_add_head_rcu(sk, new_slot)
5. pos = pos->next; <=
6. rcu_read_unlock()

In step 5, we wrongly moved from old_slot to new_slot.

Perhaps the similar codes in udp_lib_rehash() for hslot2 also need a fix.

Thanks.
-- 
Philo