sctp: fix busy polling

[ Upstream commit a562c0a2d651e040681b0bfce9b4d229ac3b0b8c ]

Busy polling while holding the socket lock makes litle sense,
because incoming packets wont reach our receive queue.

Fixes: 8465a5fcd1ce ("sctp: add support for busy polling to sctp protocol")
Reported-by: Jacob Moroni <jmoroni@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 5fb02bb..6b9fcdb 100644 (file)
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -2102,6 +2102,10 @@ static int sctp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
        if (unlikely(flags & MSG_ERRQUEUE))
                return inet_recv_error(sk, msg, len, addr_len);
 
+       if (sk_can_busy_loop(sk) &&
+           skb_queue_empty_lockless(&sk->sk_receive_queue))
+               sk_busy_loop(sk, flags & MSG_DONTWAIT);
+
        lock_sock(sk);
 
        if (sctp_style(sk, TCP) && !sctp_sstate(sk, ESTABLISHED) &&
@@ -9046,12 +9050,6 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, int *err)
                if (sk->sk_shutdown & RCV_SHUTDOWN)
                        break;
 
-               if (sk_can_busy_loop(sk)) {
-                       sk_busy_loop(sk, flags & MSG_DONTWAIT);
-
-                       if (!skb_queue_empty_lockless(&sk->sk_receive_queue))
-                               continue;
-               }
 
                /* User doesn't want to wait.  */
                error = -EAGAIN;