tcp: relax listening_hash operations

softirq handlers use RCU protection to lookup listeners,
and write operations all happen from process context.
We do not need to block BH for dump operations.

Also SYN_RECV since request sockets are stored in the ehash table :

 1) inet_diag_dump_icsk() no longer need to clear
    cb->args[3] and cb->args[4] that were used as cursors while
    iterating the old per listener hash table.

 2) Also factorize a test : No need to scan listening_hash[]
    if r->id.idiag_dport is not zero.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/inet_diag.c

@@ -863,7 +863,7 @@ void inet_diag_dump_icsk(struct inet_hashinfo *hashinfo, struct sk_buff *skb,
 	s_num = num = cb->args[2];
 
 	if (cb->args[0] == 0) {
-		if (!(idiag_states & TCPF_LISTEN))
+		if (!(idiag_states & TCPF_LISTEN) || r->id.idiag_dport)
 			goto skip_listen_ht;
 
 		for (i = s_i; i < INET_LHTABLE_SIZE; i++) {
@@ -872,7 +872,7 @@ void inet_diag_dump_icsk(struct inet_hashinfo *hashinfo, struct sk_buff *skb,
 
 			num = 0;
 			ilb = &hashinfo->listening_hash[i];
-			spin_lock_bh(&ilb->lock);
+			spin_lock(&ilb->lock);
 			sk_for_each(sk, &ilb->head) {
 				struct inet_sock *inet = inet_sk(sk);
 
@@ -892,26 +892,18 @@ void inet_diag_dump_icsk(struct inet_hashinfo *hashinfo, struct sk_buff *skb,
 				    r->id.idiag_sport)
 					goto next_listen;
 
-				if (r->id.idiag_dport ||
-				    cb->args[3] > 0)
-					goto next_listen;
-
 				if (inet_csk_diag_dump(sk, skb, cb, r,
 						       bc, net_admin) < 0) {
-					spin_unlock_bh(&ilb->lock);
+					spin_unlock(&ilb->lock);
 					goto done;
 				}
 
 next_listen:
-				cb->args[3] = 0;
-				cb->args[4] = 0;
 				++num;
 			}
-			spin_unlock_bh(&ilb->lock);
+			spin_unlock(&ilb->lock);
 
 			s_num = 0;
-			cb->args[3] = 0;
-			cb->args[4] = 0;
 		}
 skip_listen_ht:
 		cb->args[0] = 1;

net/ipv4/tcp_ipv4.c

@@ -1893,7 +1893,7 @@ static void *listening_get_next(struct seq_file *seq, void *cur)
 	if (!sk) {
 get_head:
 		ilb = &tcp_hashinfo.listening_hash[st->bucket];
-		spin_lock_bh(&ilb->lock);
+		spin_lock(&ilb->lock);
 		sk = sk_head(&ilb->head);
 		st->offset = 0;
 		goto get_sk;
@@ -1911,7 +1911,7 @@ static void *listening_get_next(struct seq_file *seq, void *cur)
 			return sk;
 		icsk = inet_csk(sk);
 	}
-	spin_unlock_bh(&ilb->lock);
+	spin_unlock(&ilb->lock);
 	st->offset = 0;
 	if (++st->bucket < INET_LHTABLE_SIZE)
 		goto get_head;
@@ -2119,7 +2119,7 @@ static void tcp_seq_stop(struct seq_file *seq, void *v)
 	switch (st->state) {
 	case TCP_SEQ_STATE_LISTENING:
 		if (v != SEQ_START_TOKEN)
-			spin_unlock_bh(&tcp_hashinfo.listening_hash[st->bucket].lock);
+			spin_unlock(&tcp_hashinfo.listening_hash[st->bucket].lock);
 		break;
 	case TCP_SEQ_STATE_ESTABLISHED:
 		if (v)