tcp: annotate data-races around rskq_defer_accept

do_tcp_getsockopt() reads rskq_defer_accept while another cpu
might change its value.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230719212857.3943972-9-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/ipv4/tcp.c

@@ -3594,9 +3594,9 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 
 	case TCP_DEFER_ACCEPT:
 		/* Translate value in seconds to number of retransmits */
-		icsk->icsk_accept_queue.rskq_defer_accept =
-			secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
-					TCP_RTO_MAX / HZ);
+		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:
@@ -4002,8 +4002,9 @@ int do_tcp_getsockopt(struct sock *sk, int level,
 			val = (val ? : READ_ONCE(net->ipv4.sysctl_tcp_fin_timeout)) / HZ;
 		break;
 	case TCP_DEFER_ACCEPT:
-		val = retrans_to_secs(icsk->icsk_accept_queue.rskq_defer_accept,
-				      TCP_TIMEOUT_INIT / HZ, TCP_RTO_MAX / HZ);
+		val = READ_ONCE(icsk->icsk_accept_queue.rskq_defer_accept);
+		val = retrans_to_secs(val, TCP_TIMEOUT_INIT / HZ,
+				      TCP_RTO_MAX / HZ);
 		break;
 	case TCP_WINDOW_CLAMP:
 		val = tp->window_clamp;