Date:   Fri, 6 Jul 2018 15:22:36 +0200
From:   Jon Maloy <jon.maloy@...csson.com>
To:     <davem@...emloft.net>, <netdev@...r.kernel.org>
CC:     <mohan.krishna.ghanta.krishnamurthy@...csson.com>,
        <tung.q.nguyen@...tech.com.au>, <hoang.h.le@...tech.com.au>,
        <jon.maloy@...csson.com>, <canh.d.luu@...tech.com.au>,
        <ying.xue@...driver.com>, <tipc-discussion@...ts.sourceforge.net>
Subject: [net-next  1/1] tipc: extend link reset criteria for stale packet retransmission

Currently a link is declared stale and reset if there has been 100
repeated attempts to retransmit the same packet. However, in certain
infrastructures we see that packet (NACK) duplicates and delays may
cause such retransmit attempts to occur at a high rate, so that the
peer doesn't have a reasonable chance to acknowledge the reception
before the 100-limit is hit. This may take much less than the
stipulated link tolerance time, and despite that probe/probe replies
otherwise go through as normal.

We now extend the criteria for link reset to also being time based.
I.e., we don't reset the link until the link tolerance time is passed
AND we have made 100 retransmissions attempts.

Acked-by: Ying Xue <ying.xue@...driver.com>
Signed-off-by: Jon Maloy <jon.maloy@...csson.com>
---
 net/tipc/link.c | 43 ++++++++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/net/tipc/link.c b/net/tipc/link.c
index 6386032..ec4d283 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -106,7 +106,8 @@ struct tipc_stats {
  * @backlogq: queue for messages waiting to be sent
  * @snt_nxt: next sequence number to use for outbound messages
  * @last_retransmitted: sequence number of most recently retransmitted message
- * @stale_count: # of identical retransmit requests made by peer
+ * @stale_cnt: counter for number of identical retransmit attempts
+ * @stale_limit: time when repeated identical retransmits must force link reset
  * @ackers: # of peers that needs to ack each packet before it can be released
  * @acked: # last packet acked by a certain peer. Used for broadcast.
  * @rcv_nxt: next sequence number to expect for inbound messages
@@ -161,7 +162,8 @@ struct tipc_link {
 	u16 snd_nxt;
 	u16 last_retransm;
 	u16 window;
-	u32 stale_count;
+	u16 stale_cnt;
+	unsigned long stale_limit;
 
 	/* Reception */
 	u16 rcv_nxt;
@@ -860,7 +862,7 @@ void tipc_link_reset(struct tipc_link *l)
 	l->acked = 0;
 	l->silent_intv_cnt = 0;
 	l->rst_cnt = 0;
-	l->stale_count = 0;
+	l->stale_cnt = 0;
 	l->bc_peer_is_up = false;
 	memset(&l->mon_state, 0, sizeof(l->mon_state));
 	tipc_link_reset_stats(l);
@@ -997,39 +999,41 @@ static void link_retransmit_failure(struct tipc_link *l, struct sk_buff *skb)
 		msg_seqno(hdr), msg_prevnode(hdr), msg_orignode(hdr));
 }
 
-int tipc_link_retrans(struct tipc_link *l, struct tipc_link *nacker,
+/* tipc_link_retrans() - retransmit one or more packets
+ * @l: the link to transmit on
+ * @r: the receiving link ordering the retransmit. Same as l if unicast
+ * @from: retransmit from (inclusive) this sequence number
+ * @to: retransmit to (inclusive) this sequence number
+ * xmitq: queue for accumulating the retransmitted packets
+ */
+int tipc_link_retrans(struct tipc_link *l, struct tipc_link *r,
 		      u16 from, u16 to, struct sk_buff_head *xmitq)
 {
 	struct sk_buff *_skb, *skb = skb_peek(&l->transmq);
-	struct tipc_msg *hdr;
-	u16 ack = l->rcv_nxt - 1;
 	u16 bc_ack = l->bc_rcvlink->rcv_nxt - 1;
+	u16 ack = l->rcv_nxt - 1;
+	struct tipc_msg *hdr;
 
 	if (!skb)
 		return 0;
 
 	/* Detect repeated retransmit failures on same packet */
-	if (nacker->last_retransm != buf_seqno(skb)) {
-		nacker->last_retransm = buf_seqno(skb);
-		nacker->stale_count = 1;
-	} else if (++nacker->stale_count > 100) {
+	if (r->last_retransm != buf_seqno(skb)) {
+		r->last_retransm = buf_seqno(skb);
+		r->stale_limit = jiffies + msecs_to_jiffies(l->tolerance);
+	} else if (++r->stale_cnt > 99 && time_after(jiffies, r->stale_limit)) {
 		link_retransmit_failure(l, skb);
-		nacker->stale_count = 0;
 		if (link_is_bc_sndlink(l))
 			return TIPC_LINK_DOWN_EVT;
 		return tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
 	}
 
-	/* Move forward to where retransmission should start */
 	skb_queue_walk(&l->transmq, skb) {
-		if (!less(buf_seqno(skb), from))
-			break;
-	}
-
-	skb_queue_walk_from(&l->transmq, skb) {
-		if (more(buf_seqno(skb), to))
-			break;
 		hdr = buf_msg(skb);
+		if (less(msg_seqno(hdr), from))
+			continue;
+		if (more(msg_seqno(hdr), to))
+			break;
 		_skb = __pskb_copy(skb, MIN_H_SIZE, GFP_ATOMIC);
 		if (!_skb)
 			return 0;
@@ -1272,6 +1276,7 @@ int tipc_link_rcv(struct tipc_link *l, struct sk_buff *skb,
 
 		/* Forward queues and wake up waiting users */
 		if (likely(tipc_link_release_pkts(l, msg_ack(hdr)))) {
+			l->stale_cnt = 0;
 			tipc_link_advance_backlog(l, xmitq);
 			if (unlikely(!skb_queue_empty(&l->wakeupq)))
 				link_prepare_wakeup(l);
-- 
2.1.4

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