net: use skb_queue_empty_lockless() in busy poll contexts

[ Upstream commit 3f926af3f4d688e2e11e7f8ed04e277a14d4d4a4 ]

Busy polling usually runs without locks.
Let's use skb_queue_empty_lockless() instead of skb_queue_empty()

Also uses READ_ONCE() in __skb_try_recv_datagram() to address
a similar potential problem.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/crypto/chelsio/chtls/chtls_io.c

@@ -1716,7 +1716,7 @@ int chtls_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		return peekmsg(sk, msg, len, nonblock, flags);
 
 	if (sk_can_busy_loop(sk) &&
-	    skb_queue_empty(&sk->sk_receive_queue) &&
+	    skb_queue_empty_lockless(&sk->sk_receive_queue) &&
 	    sk->sk_state == TCP_ESTABLISHED)
 		sk_busy_loop(sk, nonblock);
 

net/core/datagram.c

@@ -279,7 +279,7 @@ struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags,
 			break;
 
 		sk_busy_loop(sk, flags & MSG_DONTWAIT);
-	} while (sk->sk_receive_queue.prev != *last);
+	} while (READ_ONCE(sk->sk_receive_queue.prev) != *last);
 
 	error = -EAGAIN;
 

net/core/sock.c

@@ -3483,7 +3483,7 @@ bool sk_busy_loop_end(void *p, unsigned long start_time)
 {
 	struct sock *sk = p;
 
-	return !skb_queue_empty(&sk->sk_receive_queue) ||
+	return !skb_queue_empty_lockless(&sk->sk_receive_queue) ||
 	       sk_busy_loop_timeout(sk, start_time);
 }
 EXPORT_SYMBOL(sk_busy_loop_end);

net/ipv4/tcp.c

@@ -1948,7 +1948,7 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
 	if (unlikely(flags & MSG_ERRQUEUE))
 		return inet_recv_error(sk, msg, len, addr_len);
 
-	if (sk_can_busy_loop(sk) && skb_queue_empty(&sk->sk_receive_queue) &&
+	if (sk_can_busy_loop(sk) && skb_queue_empty_lockless(&sk->sk_receive_queue) &&
 	    (sk->sk_state == TCP_ESTABLISHED))
 		sk_busy_loop(sk, nonblock);
 

net/sctp/socket.c

@@ -8334,7 +8334,7 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags,
 		if (sk_can_busy_loop(sk)) {
 			sk_busy_loop(sk, noblock);
 
-			if (!skb_queue_empty(&sk->sk_receive_queue))
+			if (!skb_queue_empty_lockless(&sk->sk_receive_queue))
 				continue;
 		}