net: annotate lockless accesses to sk->sk_ack_backlog

sk->sk_ack_backlog can be read without any lock being held.
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

@@ -859,17 +859,17 @@ static inline gfp_t sk_gfp_mask(const struct sock *sk, gfp_t gfp_mask)
 
 static inline void sk_acceptq_removed(struct sock *sk)
 {
-	sk->sk_ack_backlog--;
+	WRITE_ONCE(sk->sk_ack_backlog, sk->sk_ack_backlog - 1);
 }
 
 static inline void sk_acceptq_added(struct sock *sk)
 {
-	sk->sk_ack_backlog++;
+	WRITE_ONCE(sk->sk_ack_backlog, sk->sk_ack_backlog + 1);
 }
 
 static inline bool sk_acceptq_is_full(const struct sock *sk)
 {
-	return sk->sk_ack_backlog > sk->sk_max_ack_backlog;
+	return READ_ONCE(sk->sk_ack_backlog) > sk->sk_max_ack_backlog;
 }
 
 /*

net/ipv4/tcp.c

@@ -3225,7 +3225,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 		 * tcpi_unacked -> Number of children ready for accept()
 		 * tcpi_sacked  -> max backlog
 		 */
-		info->tcpi_unacked = sk->sk_ack_backlog;
+		info->tcpi_unacked = READ_ONCE(sk->sk_ack_backlog);
 		info->tcpi_sacked = sk->sk_max_ack_backlog;
 		return;
 	}

net/ipv4/tcp_diag.c

@@ -21,7 +21,7 @@ static void tcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
 	struct tcp_info *info = _info;
 
 	if (inet_sk_state_load(sk) == TCP_LISTEN) {
-		r->idiag_rqueue = sk->sk_ack_backlog;
+		r->idiag_rqueue = READ_ONCE(sk->sk_ack_backlog);
 		r->idiag_wqueue = sk->sk_max_ack_backlog;
 	} else if (sk->sk_type == SOCK_STREAM) {
 		const struct tcp_sock *tp = tcp_sk(sk);

net/ipv4/tcp_ipv4.c

@@ -2451,7 +2451,7 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
 
 	state = inet_sk_state_load(sk);
 	if (state == TCP_LISTEN)
-		rx_queue = sk->sk_ack_backlog;
+		rx_queue = READ_ONCE(sk->sk_ack_backlog);
 	else
 		/* Because we don't lock the socket,
 		 * we might find a transient negative value.

net/ipv6/tcp_ipv6.c

@@ -1891,7 +1891,7 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
 
 	state = inet_sk_state_load(sp);
 	if (state == TCP_LISTEN)
-		rx_queue = sp->sk_ack_backlog;
+		rx_queue = READ_ONCE(sp->sk_ack_backlog);
 	else
 		/* Because we don't lock the socket,
 		 * we might find a transient negative value.

net/sched/em_meta.c

@@ -521,7 +521,7 @@ META_COLLECTOR(int_sk_ack_bl)
 		*err = -1;
 		return;
 	}
-	dst->value = sk->sk_ack_backlog;
+	dst->value = READ_ONCE(sk->sk_ack_backlog);
 }
 
 META_COLLECTOR(int_sk_max_ack_bl)

net/sctp/diag.c

@@ -425,7 +425,7 @@ static void sctp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
 		r->idiag_rqueue = atomic_read(&infox->asoc->rmem_alloc);
 		r->idiag_wqueue = infox->asoc->sndbuf_used;
 	} else {
-		r->idiag_rqueue = sk->sk_ack_backlog;
+		r->idiag_rqueue = READ_ONCE(sk->sk_ack_backlog);
 		r->idiag_wqueue = sk->sk_max_ack_backlog;
 	}
 	if (infox->sctpinfo)