txhash: fix sk->sk_txrehash default

This code fix a bug that sk->sk_txrehash gets its default enable
value from sysctl_txrehash only when the socket is a TCP listener.

We should have sysctl_txrehash to set the default sk->sk_txrehash,
no matter TCP, nor listerner/connector.

Tested by following packetdrill:
  0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
  +0 socket(..., SOCK_DGRAM, IPPROTO_UDP) = 4
  // SO_TXREHASH == 74, default to sysctl_txrehash == 1
  +0 getsockopt(3, SOL_SOCKET, 74, [1], [4]) = 0
  +0 getsockopt(4, SOL_SOCKET, 74, [1], [4]) = 0

Fixes: 2685924 ("txhash: Add socket option to control TX hash rethink behavior")
Signed-off-by: Kevin Yang <yyd@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: yydcool

net/core/sock.c

@@ -1531,6 +1531,8 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 			ret = -EINVAL;
 			break;
 		}
+		if ((u8)val == SOCK_TXREHASH_DEFAULT)
+			val = READ_ONCE(sock_net(sk)->core.sysctl_txrehash);
 		/* Paired with READ_ONCE() in tcp_rtx_synack() */
 		WRITE_ONCE(sk->sk_txrehash, (u8)val);
 		break;
@@ -3451,7 +3453,6 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 	sk->sk_pacing_rate = ~0UL;
 	WRITE_ONCE(sk->sk_pacing_shift, 10);
 	sk->sk_incoming_cpu = -1;
-	sk->sk_txrehash = SOCK_TXREHASH_DEFAULT;
 
 	sk_rx_queue_clear(sk);
 	/*

net/ipv4/af_inet.c

@@ -347,6 +347,7 @@ static int inet_create(struct net *net, struct socket *sock, int protocol,
 	sk->sk_destruct	   = inet_sock_destruct;
 	sk->sk_protocol	   = protocol;
 	sk->sk_backlog_rcv = sk->sk_prot->backlog_rcv;
+	sk->sk_txrehash = READ_ONCE(net->core.sysctl_txrehash);
 
 	inet->uc_ttl	= -1;
 	inet->mc_loop	= 1;

net/ipv4/inet_connection_sock.c

@@ -1225,9 +1225,6 @@ int inet_csk_listen_start(struct sock *sk)
 	sk->sk_ack_backlog = 0;
 	inet_csk_delack_init(sk);
 
-	if (sk->sk_txrehash == SOCK_TXREHASH_DEFAULT)
-		sk->sk_txrehash = READ_ONCE(sock_net(sk)->core.sysctl_txrehash);
-
 	/* There is race window here: we announce ourselves listening,
 	 * but this transition is still not validated by get_port().
 	 * It is OK, because this socket enters to hash table only

net/ipv6/af_inet6.c

@@ -222,6 +222,7 @@ static int inet6_create(struct net *net, struct socket *sock, int protocol,
 	np->pmtudisc	= IPV6_PMTUDISC_WANT;
 	np->repflow	= net->ipv6.sysctl.flowlabel_reflect & FLOWLABEL_REFLECT_ESTABLISHED;
 	sk->sk_ipv6only	= net->ipv6.sysctl.bindv6only;
+	sk->sk_txrehash = READ_ONCE(net->core.sysctl_txrehash);
 
 	/* Init the ipv4 part of the socket since we can have sockets
 	 * using v6 API for ipv4.