[PATCH 4.4 30/31] rds: avoid unenecessary cong_update in loop transport

[Greg Kroah-Hartman]

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

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

From: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>

commit f1693c63ab133d16994cc50f773982b5905af264 upstream.

Loop transport which is self loopback, remote port congestion
update isn't relevant. Infact the xmit path already ignores it.
Receive path needs to do the same.

Reported-by: syzbot+4c20b3866171ce8441d2@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Sowmini Varadhan <sowmini.varadhan@xxxxxxxxxx>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/rds/loop.c |    1 +
 net/rds/rds.h  |    5 +++++
 net/rds/recv.c |    5 +++++
 3 files changed, 11 insertions(+)

--- a/net/rds/loop.c
+++ b/net/rds/loop.c
@@ -191,4 +191,5 @@ struct rds_transport rds_loop_transport
 	.inc_copy_to_user	= rds_message_inc_copy_to_user,
 	.inc_free		= rds_loop_inc_free,
 	.t_name			= "loopback",
+	.t_type			= RDS_TRANS_LOOP,
 };
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -401,6 +401,11 @@ struct rds_notifier {
 	int			n_status;
 };
 
+/* Available as part of RDS core, so doesn't need to participate
+ * in get_preferred transport etc
+ */
+#define	RDS_TRANS_LOOP	3
+
 /**
  * struct rds_transport -  transport specific behavioural hooks
  *
--- a/net/rds/recv.c
+++ b/net/rds/recv.c
@@ -76,6 +76,11 @@ static void rds_recv_rcvbuf_delta(struct
 		return;
 
 	rs->rs_rcv_bytes += delta;
+
+	/* loop transport doesn't send/recv congestion updates */
+	if (rs->rs_transport->t_type == RDS_TRANS_LOOP)
+		return;
+
 	now_congested = rs->rs_rcv_bytes > rds_sk_rcvbuf(rs);
 
 	rdsdebug("rs %p (%pI4:%u) recv bytes %d buf %d "