net: annotate lockless accesses to sk->sk_max_ack_backlog

sk->sk_max_ack_backlog can be read without any lock being held
at least in TCP/DCCP cases.

We need to use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing
and/or potential KCSAN warnings.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: edumazet

include/net/sock.h

@@ -869,7 +869,7 @@ static inline void sk_acceptq_added(struct sock *sk)
 
 static inline bool sk_acceptq_is_full(const struct sock *sk)
 {
-	return READ_ONCE(sk->sk_ack_backlog) > sk->sk_max_ack_backlog;
+	return READ_ONCE(sk->sk_ack_backlog) > READ_ONCE(sk->sk_max_ack_backlog);
 }
 
 /*

net/dccp/proto.c

@@ -944,7 +944,7 @@ int inet_dccp_listen(struct socket *sock, int backlog)
 	if (!((1 << old_state) & (DCCPF_CLOSED | DCCPF_LISTEN)))
 		goto out;
 
-	sk->sk_max_ack_backlog = backlog;
+	WRITE_ONCE(sk->sk_max_ack_backlog, backlog);
 	/* Really, if the socket is already in listen state
 	 * we can only allow the backlog to be adjusted.
 	 */

net/ipv4/af_inet.c

@@ -208,7 +208,7 @@ int inet_listen(struct socket *sock, int backlog)
 	if (!((1 << old_state) & (TCPF_CLOSE | TCPF_LISTEN)))
 		goto out;
 
-	sk->sk_max_ack_backlog = backlog;
+	WRITE_ONCE(sk->sk_max_ack_backlog, backlog);
 	/* Really, if the socket is already in listen state
 	 * we can only allow the backlog to be adjusted.
 	 */

net/ipv4/inet_connection_sock.c

@@ -716,7 +716,7 @@ static void reqsk_timer_handler(struct timer_list *t)
 	 * ones are about to clog our table.
 	 */
 	qlen = reqsk_queue_len(queue);
-	if ((qlen << 1) > max(8U, sk_listener->sk_max_ack_backlog)) {
+	if ((qlen << 1) > max(8U, READ_ONCE(sk_listener->sk_max_ack_backlog))) {
 		int young = reqsk_queue_len_young(queue) << 1;
 
 		while (thresh > 2) {

net/ipv4/tcp.c

@@ -3226,7 +3226,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 		 * tcpi_sacked  -> max backlog
 		 */
 		info->tcpi_unacked = READ_ONCE(sk->sk_ack_backlog);
-		info->tcpi_sacked = sk->sk_max_ack_backlog;
+		info->tcpi_sacked = READ_ONCE(sk->sk_max_ack_backlog);
 		return;
 	}
 

net/ipv4/tcp_diag.c

@@ -22,7 +22,7 @@ static void tcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
 
 	if (inet_sk_state_load(sk) == TCP_LISTEN) {
 		r->idiag_rqueue = READ_ONCE(sk->sk_ack_backlog);
-		r->idiag_wqueue = sk->sk_max_ack_backlog;
+		r->idiag_wqueue = READ_ONCE(sk->sk_max_ack_backlog);
 	} else if (sk->sk_type == SOCK_STREAM) {
 		const struct tcp_sock *tp = tcp_sk(sk);
 

net/sched/em_meta.c

@@ -532,7 +532,7 @@ META_COLLECTOR(int_sk_max_ack_bl)
 		*err = -1;
 		return;
 	}
-	dst->value = sk->sk_max_ack_backlog;
+	dst->value = READ_ONCE(sk->sk_max_ack_backlog);
 }
 
 META_COLLECTOR(int_sk_prio)

net/sctp/diag.c

@@ -426,7 +426,7 @@ static void sctp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
 		r->idiag_wqueue = infox->asoc->sndbuf_used;
 	} else {
 		r->idiag_rqueue = READ_ONCE(sk->sk_ack_backlog);
-		r->idiag_wqueue = sk->sk_max_ack_backlog;
+		r->idiag_wqueue = READ_ONCE(sk->sk_max_ack_backlog);
 	}
 	if (infox->sctpinfo)
 		sctp_get_sctp_info(sk, infox->asoc, infox->sctpinfo);

net/sctp/socket.c

@@ -8376,7 +8376,7 @@ static int sctp_listen_start(struct sock *sk, int backlog)
 		}
 	}
 
-	sk->sk_max_ack_backlog = backlog;
+	WRITE_ONCE(sk->sk_max_ack_backlog, backlog);
 	return sctp_hash_endpoint(ep);
 }
 
@@ -8430,7 +8430,7 @@ int sctp_inet_listen(struct socket *sock, int backlog)
 
 	/* If we are already listening, just update the backlog */
 	if (sctp_sstate(sk, LISTENING))
-		sk->sk_max_ack_backlog = backlog;
+		WRITE_ONCE(sk->sk_max_ack_backlog, backlog);
 	else {
 		err = sctp_listen_start(sk, backlog);
 		if (err)