net: mark racy access on sk->sk_rcvbuf

sk->sk_rcvbuf in __sock_queue_rcv_skb() and __sk_receive_skb() can be
changed by other threads. Mark this as benign using READ_ONCE().

This patch is aimed at reducing the number of benign races reported by
KCSAN in order to focus future debugging effort on harmful races.
Signed-off-by: linke li <lilinke99@qq.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -482,7 +482,7 @@ int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	unsigned long flags;
 	struct sk_buff_head *list = &sk->sk_receive_queue;
 
-	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) {
+	if (atomic_read(&sk->sk_rmem_alloc) >= READ_ONCE(sk->sk_rcvbuf)) {
 		atomic_inc(&sk->sk_drops);
 		trace_sock_rcvqueue_full(sk, skb);
 		return -ENOMEM;
@@ -552,7 +552,7 @@ int __sk_receive_skb(struct sock *sk, struct sk_buff *skb,
 
 	skb->dev = NULL;
 
-	if (sk_rcvqueues_full(sk, sk->sk_rcvbuf)) {
+	if (sk_rcvqueues_full(sk, READ_ONCE(sk->sk_rcvbuf))) {
 		atomic_inc(&sk->sk_drops);
 		goto discard_and_relse;
 	}