tcp: set TCP_LINGER2 locklessly

tp->linger2 can be set locklessly as long as readers
use READ_ONCE().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -2865,7 +2865,7 @@ void __tcp_close(struct sock *sk, long timeout)
 
 	if (sk->sk_state == TCP_FIN_WAIT2) {
 		struct tcp_sock *tp = tcp_sk(sk);
-		if (tp->linger2 < 0) {
+		if (READ_ONCE(tp->linger2) < 0) {
 			tcp_set_state(sk, TCP_CLOSE);
 			tcp_send_active_reset(sk, GFP_ATOMIC);
 			__NET_INC_STATS(sock_net(sk),
@@ -3471,6 +3471,14 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		return tcp_sock_set_keepintvl(sk, val);
 	case TCP_KEEPCNT:
 		return tcp_sock_set_keepcnt(sk, val);
+	case TCP_LINGER2:
+		if (val < 0)
+			WRITE_ONCE(tp->linger2, -1);
+		else if (val > TCP_FIN_TIMEOUT_MAX / HZ)
+			WRITE_ONCE(tp->linger2, TCP_FIN_TIMEOUT_MAX);
+		else
+			WRITE_ONCE(tp->linger2, val * HZ);
+		return 0;
 	}
 
 	sockopt_lock_sock(sk);
@@ -3576,15 +3584,6 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 			tp->save_syn = val;
 		break;
 
-	case TCP_LINGER2:
-		if (val < 0)
-			WRITE_ONCE(tp->linger2, -1);
-		else if (val > TCP_FIN_TIMEOUT_MAX / HZ)
-			WRITE_ONCE(tp->linger2, TCP_FIN_TIMEOUT_MAX);
-		else
-			WRITE_ONCE(tp->linger2, val * HZ);
-		break;
-
 	case TCP_DEFER_ACCEPT:
 		/* Translate value in seconds to number of retransmits */
 		WRITE_ONCE(icsk->icsk_accept_queue.rskq_defer_accept,

net/ipv4/tcp_input.c

@@ -6624,7 +6624,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 			break;
 		}
 
-		if (tp->linger2 < 0) {
+		if (READ_ONCE(tp->linger2) < 0) {
 			tcp_done(sk);
 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
 			return 1;

net/ipv4/tcp_timer.c

@@ -714,7 +714,7 @@ static void tcp_keepalive_timer (struct timer_list *t)
 
 	tcp_mstamp_refresh(tp);
 	if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
-		if (tp->linger2 >= 0) {
+		if (READ_ONCE(tp->linger2) >= 0) {
 			const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 
 			if (tmo > 0) {