tcp: set TCP_DEFER_ACCEPT locklessly

rskq_defer_accept field can be read/written without
the need of holding the socket lock.
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

@@ -3479,6 +3479,12 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		else
 			WRITE_ONCE(tp->linger2, val * HZ);
 		return 0;
+	case TCP_DEFER_ACCEPT:
+		/* Translate value in seconds to number of retransmits */
+		WRITE_ONCE(icsk->icsk_accept_queue.rskq_defer_accept,
+			   secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
+					   TCP_RTO_MAX / HZ));
+		return 0;
 	}
 
 	sockopt_lock_sock(sk);
@@ -3584,13 +3590,6 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 			tp->save_syn = val;
 		break;
 
-	case TCP_DEFER_ACCEPT:
-		/* Translate value in seconds to number of retransmits */
-		WRITE_ONCE(icsk->icsk_accept_queue.rskq_defer_accept,
-			   secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
-					   TCP_RTO_MAX / HZ));
-		break;
-
 	case TCP_WINDOW_CLAMP:
 		err = tcp_set_window_clamp(sk, val);
 		break;

net/ipv4/tcp_input.c

@@ -6324,7 +6324,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 		if (fastopen_fail)
 			return -1;
 		if (sk->sk_write_pending ||
-		    icsk->icsk_accept_queue.rskq_defer_accept ||
+		    READ_ONCE(icsk->icsk_accept_queue.rskq_defer_accept) ||
 		    inet_csk_in_pingpong_mode(sk)) {
 			/* Save one ACK. Data will be ready after
 			 * several ticks, if write_pending is set.

net/ipv4/tcp_minisocks.c

@@ -792,7 +792,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 		return sk;
 
 	/* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
-	if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
+	if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) &&
 	    TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
 		inet_rsk(req)->acked = 1;
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);