rxrpc: Add keepalive for a call

We need to transmit a packet every so often to act as a keepalive for the
peer (which has a timeout from the last time it received a packet) and also
to prevent any intervening firewalls from closing the route.

Do this by resetting a timer every time we transmit a packet.  If the timer
ever expires, we transmit a PING ACK packet and thereby also elicit a PING
RESPONSE ACK from the other side - which prevents our last-rx timeout from
expiring.

The timer is set to 1/6 of the last-rx timeout so that we can detect the
other side going away if it misses 6 replies in a row.

This is particularly necessary for servers where the processing of the
service function may take a significant amount of time.

Signed-off-by: David Howells <dhowells@redhat.com>

3 files changed, 34 insertions, 0 deletions

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 7e7b817..cdcbc79 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -519,6 +519,7 @@ struct rxrpc_call {
 	unsigned long		ack_lost_at;	/* When ACK is figured as lost */
 	unsigned long		resend_at;	/* When next resend needs to happen */
 	unsigned long		ping_at;	/* When next to send a ping */
+	unsigned long		keepalive_at;	/* When next to send a keepalive ping */
 	unsigned long		expect_rx_by;	/* When we expect to get a packet by */
 	unsigned long		expect_req_by;	/* When we expect to get a request DATA packet by */
 	unsigned long		expect_term_by;	/* When we expect call termination by */
diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index c65666b..bda952f 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -366,6 +366,15 @@ recheck_state:
 		set_bit(RXRPC_CALL_EV_ACK_LOST, &call->events);
 	}
 
+	t = READ_ONCE(call->keepalive_at);
+	if (time_after_eq(now, t)) {
+		trace_rxrpc_timer(call, rxrpc_timer_exp_keepalive, now);
+		cmpxchg(&call->keepalive_at, t, now + MAX_JIFFY_OFFSET);
+		rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, 0, true, true,
+				  rxrpc_propose_ack_ping_for_keepalive);
+		set_bit(RXRPC_CALL_EV_PING, &call->events);
+	}
+
 	t = READ_ONCE(call->ping_at);
 	if (time_after_eq(now, t)) {
 		trace_rxrpc_timer(call, rxrpc_timer_exp_ping, now);
@@ -423,6 +432,7 @@ recheck_state:
 	set(call->ack_at);
 	set(call->ack_lost_at);
 	set(call->resend_at);
+	set(call->keepalive_at);
 	set(call->ping_at);
 
 	now = jiffies;
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index efe06ed..42410e9 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -33,6 +33,24 @@ struct rxrpc_abort_buffer {
 };
 
 /*
+ * Arrange for a keepalive ping a certain time after we last transmitted.  This
+ * lets the far side know we're still interested in this call and helps keep
+ * the route through any intervening firewall open.
+ *
+ * Receiving a response to the ping will prevent the ->expect_rx_by timer from
+ * expiring.
+ */
+static void rxrpc_set_keepalive(struct rxrpc_call *call)
+{
+	unsigned long now = jiffies, keepalive_at = call->next_rx_timo / 6;
+
+	keepalive_at += now;
+	WRITE_ONCE(call->keepalive_at, keepalive_at);
+	rxrpc_reduce_call_timer(call, keepalive_at, now,
+				rxrpc_timer_set_for_keepalive);
+}
+
+/*
  * Fill out an ACK packet.
  */
 static size_t rxrpc_fill_out_ack(struct rxrpc_connection *conn,
@@ -205,6 +223,8 @@ int rxrpc_send_ack_packet(struct rxrpc_call *call, bool ping,
 				call->ackr_seen = top;
 			spin_unlock_bh(&call->lock);
 		}
+
+		rxrpc_set_keepalive(call);
 	}
 
 out:
@@ -388,6 +408,9 @@ done:
 			}
 		}
 	}
+
+	rxrpc_set_keepalive(call);
+
 	_leave(" = %d [%u]", ret, call->peer->maxdata);
 	return ret;