tcp: annotate data-races around icsk->icsk_user_timeout

This field can be read locklessly from do_tcp_getsockopt()

Fixes: dca43c7 ("tcp: Add TCP_USER_TIMEOUT socket option.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230719212857.3943972-11-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp.c

@@ -3300,7 +3300,7 @@ EXPORT_SYMBOL(tcp_sock_set_syncnt);
 void tcp_sock_set_user_timeout(struct sock *sk, u32 val)
 {
 	lock_sock(sk);
-	inet_csk(sk)->icsk_user_timeout = val;
+	WRITE_ONCE(inet_csk(sk)->icsk_user_timeout, val);
 	release_sock(sk);
 }
 EXPORT_SYMBOL(tcp_sock_set_user_timeout);
@@ -3620,7 +3620,7 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		if (val < 0)
 			err = -EINVAL;
 		else
-			icsk->icsk_user_timeout = val;
+			WRITE_ONCE(icsk->icsk_user_timeout, val);
 		break;
 
 	case TCP_FASTOPEN:
@@ -4141,7 +4141,7 @@ int do_tcp_getsockopt(struct sock *sk, int level,
 		break;
 
 	case TCP_USER_TIMEOUT:
-		val = icsk->icsk_user_timeout;
+		val = READ_ONCE(icsk->icsk_user_timeout);
 		break;
 
 	case TCP_FASTOPEN: