tcp: seq_file: Replace listening_hash with lhash2

This patch moves the tcp seq_file iteration on listeners
from the port only listening_hash to the port+addr lhash2.

When iterating from the bpf iter, the next patch will need to
lock the socket such that the bpf iter can call setsockopt (e.g. to
change the TCP_CONGESTION). To avoid locking the bucket and then locking
the sock, the bpf iter will first batch some sockets from the same bucket
and then unlock the bucket. If the bucket size is small (which
usually is), it is easier to batch the whole bucket such that it is less
likely to miss a setsockopt on a socket due to changes in the bucket.

However, the port only listening_hash could have many listeners
hashed to a bucket (e.g. many individual VIP(s):443 and also
multiple by the number of SO_REUSEPORT). We have seen bucket size in
tens of thousands range. Also, the chance of having changes
in some popular port buckets (e.g. 443) is also high.

The port+addr lhash2 was introduced to solve this large listener bucket
issue. Also, the listening_hash usage has already been replaced with
lhash2 in the fast path inet[6]_lookup_listener(). This patch follows
the same direction on moving to lhash2 and iterates the lhash2
instead of listening_hash.

Signed-off-by: Martin KaFai Lau <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Acked-by: Kuniyuki Iwashima <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

include/net/inet_hashtables.h

···
 					____cacheline_aligned_in_smp;
 };
 
+#define inet_lhash2_for_each_icsk_continue(__icsk) \
+	hlist_for_each_entry_continue(__icsk, icsk_listen_portaddr_node)
+
+#define inet_lhash2_for_each_icsk(__icsk, list) \
+	hlist_for_each_entry(__icsk, list, icsk_listen_portaddr_node)
+
 #define inet_lhash2_for_each_icsk_rcu(__icsk, list) \
 	hlist_for_each_entry_rcu(__icsk, list, icsk_listen_portaddr_node)
 

net/ipv4/tcp_ipv4.c

···
 	struct tcp_iter_state *st = seq->private;
 
 	st->offset = 0;
-	for (; st->bucket < INET_LHTABLE_SIZE; st->bucket++) {
-		struct inet_listen_hashbucket *ilb;
-		struct hlist_nulls_node *node;
+	for (; st->bucket <= tcp_hashinfo.lhash2_mask; st->bucket++) {
+		struct inet_listen_hashbucket *ilb2;
+		struct inet_connection_sock *icsk;
 		struct sock *sk;
 
-		ilb = &tcp_hashinfo.listening_hash[st->bucket];
-		if (hlist_nulls_empty(&ilb->nulls_head))
+		ilb2 = &tcp_hashinfo.lhash2[st->bucket];
+		if (hlist_empty(&ilb2->head))
 			continue;
 
-		spin_lock(&ilb->lock);
-		sk_nulls_for_each(sk, node, &ilb->nulls_head) {
+		spin_lock(&ilb2->lock);
+		inet_lhash2_for_each_icsk(icsk, &ilb2->head) {
+			sk = (struct sock *)icsk;
 			if (seq_sk_match(seq, sk))
 				return sk;
 		}
-		spin_unlock(&ilb->lock);
+		spin_unlock(&ilb2->lock);
 	}
 
 	return NULL;
···
 static void *listening_get_next(struct seq_file *seq, void *cur)
 {
 	struct tcp_iter_state *st = seq->private;
-	struct inet_listen_hashbucket *ilb;
-	struct hlist_nulls_node *node;
+	struct inet_listen_hashbucket *ilb2;
+	struct inet_connection_sock *icsk;
 	struct sock *sk = cur;
 
 	++st->num;
 	++st->offset;
 
-	sk = sk_nulls_next(sk);
-
-	sk_nulls_for_each_from(sk, node) {
+	icsk = inet_csk(sk);
+	inet_lhash2_for_each_icsk_continue(icsk) {
+		sk = (struct sock *)icsk;
 		if (seq_sk_match(seq, sk))
 			return sk;
 	}
 
-	ilb = &tcp_hashinfo.listening_hash[st->bucket];
-	spin_unlock(&ilb->lock);
+	ilb2 = &tcp_hashinfo.lhash2[st->bucket];
+	spin_unlock(&ilb2->lock);
 	++st->bucket;
 	return listening_get_first(seq);
 }
···
 
 	switch (st->state) {
 	case TCP_SEQ_STATE_LISTENING:
-		if (st->bucket >= INET_LHTABLE_SIZE)
+		if (st->bucket > tcp_hashinfo.lhash2_mask)
 			break;
 		st->state = TCP_SEQ_STATE_LISTENING;
 		rc = listening_get_first(seq);
···
 	switch (st->state) {
 	case TCP_SEQ_STATE_LISTENING:
 		if (v != SEQ_START_TOKEN)
-			spin_unlock(&tcp_hashinfo.listening_hash[st->bucket].lock);
+			spin_unlock(&tcp_hashinfo.lhash2[st->bucket].lock);
 		break;
 	case TCP_SEQ_STATE_ESTABLISHED:
 		if (v)