netdev - [PATCH net-next] sctp: fix busy polling

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Message-ID: <20231219170017.73902-1-edumazet@google.com>
Date: Tue, 19 Dec 2023 17:00:17 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, Jacob Moroni <jmoroni@...gle.com>, 
	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, Xin Long <lucien.xin@...il.com>
Subject: [PATCH net-next] sctp: fix busy polling

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@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc: Xin Long <lucien.xin@...il.com>
---
 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 5fb02bbb4b349ef9ab9c2790cccb30fb4c4e897c..6b9fcdb0952a0fe599ae5d1d1cc6fa9557a3a3bc 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;
-- 
2.43.0.472.g3155946c3a-goog