tcp: annotate data-races around tp->linger2

do_tcp_getsockopt() reads tp->linger2 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/20230719212857.3943972-8-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp.c

@@ -3585,11 +3585,11 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 
 	case TCP_LINGER2:
 		if (val < 0)
-			tp->linger2 = -1;
+			WRITE_ONCE(tp->linger2, -1);
 		else if (val > TCP_FIN_TIMEOUT_MAX / HZ)
-			tp->linger2 = TCP_FIN_TIMEOUT_MAX;
+			WRITE_ONCE(tp->linger2, TCP_FIN_TIMEOUT_MAX);
 		else
-			tp->linger2 = val * HZ;
+			WRITE_ONCE(tp->linger2, val * HZ);
 		break;
 
 	case TCP_DEFER_ACCEPT:
@@ -3997,7 +3997,7 @@ int do_tcp_getsockopt(struct sock *sk, int level,
 			READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
 		break;
 	case TCP_LINGER2:
-		val = tp->linger2;
+		val = READ_ONCE(tp->linger2);
 		if (val >= 0)
 			val = (val ? : READ_ONCE(net->ipv4.sysctl_tcp_fin_timeout)) / HZ;
 		break;