netdev - [PATCH net 2/2] RDS: TCP: Avoid rds connection churn from rogue SYNs

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Message-Id: <b768a2aabf58f282e8058cf04dfed5d682cf0110.1463579486.git.sowmini.varadhan@oracle.com>
Date:	Wed, 18 May 2016 10:06:24 -0700
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	netdev@...r.kernel.org
Cc:	davem@...emloft.net, rds-devel@....oracle.com,
	ajaykumar.hotchandani@...cle.com, sowmini.varadhan@...cle.com,
	santosh.shilimkar@...cle.com
Subject: [PATCH net 2/2] RDS: TCP: Avoid rds connection churn from rogue SYNs

When a rogue SYN is received after the connection arbitration
algorithm has converged, the incoming SYN should not needlessly
quiesce the transmit path, and it should not result in needless
TCP connection resets due to re-execution of the connection
arbitration logic.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
---
 net/rds/tcp_listen.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
index e10b422..bc387c2 100644
--- a/net/rds/tcp_listen.c
+++ b/net/rds/tcp_listen.c
@@ -132,11 +132,13 @@ int rds_tcp_accept_one(struct socket *sock)
 		 * so we must quiesce any send threads before resetting
 		 * c_transport_data.
 		 */
-		wait_event(conn->c_waitq,
-			   !test_bit(RDS_IN_XMIT, &conn->c_flags));
-		if (ntohl(inet->inet_saddr) < ntohl(inet->inet_daddr)) {
+		if (ntohl(inet->inet_saddr) < ntohl(inet->inet_daddr) ||
+		    !conn->c_outgoing) {
 			goto rst_nsk;
-		} else if (rs_tcp->t_sock) {
+		} else {
+			atomic_set(&conn->c_state, RDS_CONN_CONNECTING);
+			wait_event(conn->c_waitq,
+				   !test_bit(RDS_IN_XMIT, &conn->c_flags));
 			rds_tcp_restore_callbacks(rs_tcp->t_sock, rs_tcp);
 			conn->c_outgoing = 0;
 		}
-- 
1.7.1