af_unix: Annotate data-race of net->unx.sysctl_max_dgram_qlen.

net->unx.sysctl_max_dgram_qlen is exposed as a sysctl knob and can be
changed concurrently.

Let's use READ_ONCE() in unix_create1().

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/unix/af_unix.c

@@ -976,7 +976,7 @@ static struct sock *unix_create1(struct net *net, struct socket *sock, int kern,
 	sk->sk_hash		= unix_unbound_hash(sk);
 	sk->sk_allocation	= GFP_KERNEL_ACCOUNT;
 	sk->sk_write_space	= unix_write_space;
-	sk->sk_max_ack_backlog	= net->unx.sysctl_max_dgram_qlen;
+	sk->sk_max_ack_backlog	= READ_ONCE(net->unx.sysctl_max_dgram_qlen);
 	sk->sk_destruct		= unix_sock_destructor;
 	u = unix_sk(sk);
 	u->listener = NULL;