[PATCH 6.6 214/583] sctp: fix busy polling

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6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
Cc: Xin Long <lucien.xin@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/sctp/socket.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 5fb02bbb4b34..6b9fcdb0952a 100644
--- 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;
-- 
2.43.0







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