From: Eric Dumazet <edumazet@google.com>
Date: Wed, 23 Oct 2019 22:44:51 -0700
Subject: net: use skb_queue_empty_lockless() in busy poll contexts
Git-commit: 3f926af3f4d688e2e11e7f8ed04e277a14d4d4a4
Patch-mainline: 5.4-rc6
References: networking-stable-19_11_05

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.

[js] no nvme and chelsio in 4.12 yet.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/core/datagram.c |    2 +-
 net/core/sock.c     |    2 +-
 net/ipv4/tcp.c      |    2 +-
 net/sctp/socket.c   |    2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -274,7 +274,7 @@ struct sk_buff *__skb_try_recv_datagram(
 			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;
 
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3289,7 +3289,7 @@ bool sk_busy_loop_end(void *p, unsigned
 {
 	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);
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1653,7 +1653,7 @@ int tcp_recvmsg(struct sock *sk, struct
 	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);
 
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -7645,7 +7645,7 @@ struct sk_buff *sctp_skb_recv_datagram(s
 		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;
 		}