tcp: annotate data-races around tp->keepalive_intvl

do_tcp_getsockopt() reads tp->keepalive_intvl while another cpu
might change its value.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230719212857.3943972-5-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/tcp.h

@@ -1509,9 +1509,14 @@ void tcp_leave_memory_pressure(struct sock *sk);
 static inline int keepalive_intvl_when(const struct tcp_sock *tp)
 {
 	struct net *net = sock_net((struct sock *)tp);
+	int val;
+
+	/* Paired with WRITE_ONCE() in tcp_sock_set_keepintvl()
+	 * and do_tcp_setsockopt().
+	 */
+	val = READ_ONCE(tp->keepalive_intvl);
 
-	return tp->keepalive_intvl ? :
-		READ_ONCE(net->ipv4.sysctl_tcp_keepalive_intvl);
+	return val ? : READ_ONCE(net->ipv4.sysctl_tcp_keepalive_intvl);
 }
 
 static inline int keepalive_time_when(const struct tcp_sock *tp)

net/ipv4/tcp.c

@@ -3345,7 +3345,7 @@ int tcp_sock_set_keepintvl(struct sock *sk, int val)
 		return -EINVAL;
 
 	lock_sock(sk);
-	tcp_sk(sk)->keepalive_intvl = val * HZ;
+	WRITE_ONCE(tcp_sk(sk)->keepalive_intvl, val * HZ);
 	release_sock(sk);
 	return 0;
 }
@@ -3559,7 +3559,7 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		if (val < 1 || val > MAX_TCP_KEEPINTVL)
 			err = -EINVAL;
 		else
-			tp->keepalive_intvl = val * HZ;
+			WRITE_ONCE(tp->keepalive_intvl, val * HZ);
 		break;
 	case TCP_KEEPCNT:
 		if (val < 1 || val > MAX_TCP_KEEPCNT)