[PATCH] rds: avoid unenecessary cong_update in loop transport

[Santosh Shilimkar <santosh.shilimkar@oracle.com>]

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@syzkaller.appspotmail.com
Reviewed-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
---
 net/rds/loop.c | 1 +
 net/rds/rds.h  | 5 +++++
 net/rds/recv.c | 5 +++++
 3 files changed, 11 insertions(+)

diff --git a/net/rds/loop.c b/net/rds/loop.c
index f2bf78d..dac6218 100644
--- a/net/rds/loop.c
+++ b/net/rds/loop.c
@@ -193,4 +193,5 @@ 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,
 };
diff --git a/net/rds/rds.h b/net/rds/rds.h
index b04c333..f2272fb 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -479,6 +479,11 @@ 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
  *
diff --git a/net/rds/recv.c b/net/rds/recv.c
index dc67458..192ac6f 100644
--- a/net/rds/recv.c
+++ b/net/rds/recv.c
@@ -103,6 +103,11 @@ static void rds_recv_rcvbuf_delta(struct rds_sock *rs, struct sock *sk,
 		rds_stats_add(s_recv_bytes_added_to_socket, delta);
 	else
 		rds_stats_add(s_recv_bytes_removed_from_socket, -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 "
-- 
1.9.1