rxrpc: Fix decision on when to generate an IDLE ACK

Fix the decision on when to generate an IDLE ACK by keeping a count of the
number of packets we've received, but not yet soft-ACK'd, and the number of
packets we've processed, but not yet hard-ACK'd, rather than trying to keep
track of which DATA sequence numbers correspond to those points.

We then generate an ACK when either counter exceeds 2.  The counters are
both cleared when we transcribe the information into any sort of ACK packet
for transmission.  IDLE and DELAY ACKs are skipped if both counters are 0
(ie. no change).

Fixes: 805b21b9 ("rxrpc: Send an ACK after every few DATA packets we receive")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: David S. Miller <davem@davemloft.net>

include/trace/events/rxrpc.h

@@ -1509,7 +1509,7 @@ TRACE_EVENT(rxrpc_call_reset,
 		    __entry->call_serial = call->rx_serial;
 		    __entry->conn_serial = call->conn->hi_serial;
 		    __entry->tx_seq = call->tx_hard_ack;
-		    __entry->rx_seq = call->ackr_seen;
+		    __entry->rx_seq = call->rx_hard_ack;
 			   ),
 
 	    TP_printk("c=%08x %08x:%08x r=%08x/%08x tx=%08x rx=%08x",

net/rxrpc/ar-internal.h

@@ -680,8 +680,8 @@ struct rxrpc_call {
 	u8			ackr_reason;	/* reason to ACK */
 	rxrpc_serial_t		ackr_serial;	/* serial of packet being ACK'd */
 	rxrpc_seq_t		ackr_highest_seq; /* Higest sequence number received */
-	rxrpc_seq_t		ackr_consumed;	/* Highest packet shown consumed */
-	rxrpc_seq_t		ackr_seen;	/* Highest packet shown seen */
+	atomic_t		ackr_nr_unacked; /* Number of unacked packets */
+	atomic_t		ackr_nr_consumed; /* Number of packets needing hard ACK */
 
 	/* RTT management */
 	rxrpc_serial_t		rtt_serial[4];	/* Serial number of DATA or PING sent */

net/rxrpc/input.c

@@ -412,8 +412,8 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	enum rxrpc_call_state state;
-	unsigned int j, nr_subpackets;
-	rxrpc_serial_t serial = sp->hdr.serial, ack_serial = 0;
+	unsigned int j, nr_subpackets, nr_unacked = 0;
+	rxrpc_serial_t serial = sp->hdr.serial, ack_serial = serial;
 	rxrpc_seq_t seq0 = sp->hdr.seq, hard_ack;
 	bool immediate_ack = false, jumbo_bad = false;
 	u8 ack = 0;
@@ -569,6 +569,8 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
 			sp = NULL;
 		}
 
+		nr_unacked++;
+
 		if (last) {
 			set_bit(RXRPC_CALL_RX_LAST, &call->flags);
 			if (!ack) {
@@ -588,9 +590,14 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
 			}
 			call->rx_expect_next = seq + 1;
 		}
+		if (!ack)
+			ack_serial = serial;
 	}
 
 ack:
+	if (atomic_add_return(nr_unacked, &call->ackr_nr_unacked) > 2 && !ack)
+		ack = RXRPC_ACK_IDLE;
+
 	if (ack)
 		rxrpc_propose_ACK(call, ack, ack_serial,
 				  immediate_ack, true,

net/rxrpc/output.c

@@ -74,11 +74,18 @@ static size_t rxrpc_fill_out_ack(struct rxrpc_connection *conn,
 				 u8 reason)
 {
 	rxrpc_serial_t serial;
+	unsigned int tmp;
 	rxrpc_seq_t hard_ack, top, seq;
 	int ix;
 	u32 mtu, jmax;
 	u8 *ackp = pkt->acks;
 
+	tmp = atomic_xchg(&call->ackr_nr_unacked, 0);
+	tmp |= atomic_xchg(&call->ackr_nr_consumed, 0);
+	if (!tmp && (reason == RXRPC_ACK_DELAY ||
+		     reason == RXRPC_ACK_IDLE))
+		return 0;
+
 	/* Barrier against rxrpc_input_data(). */
 	serial = call->ackr_serial;
 	hard_ack = READ_ONCE(call->rx_hard_ack);
@@ -223,6 +230,10 @@ int rxrpc_send_ack_packet(struct rxrpc_call *call, bool ping,
 	n = rxrpc_fill_out_ack(conn, call, pkt, &hard_ack, &top, reason);
 
 	spin_unlock_bh(&call->lock);
+	if (n == 0) {
+		kfree(pkt);
+		return 0;
+	}
 
 	iov[0].iov_base	= pkt;
 	iov[0].iov_len	= sizeof(pkt->whdr) + sizeof(pkt->ack) + n;
@@ -259,13 +270,6 @@ int rxrpc_send_ack_packet(struct rxrpc_call *call, bool ping,
 					  ntohl(pkt->ack.serial),
 					  false, true,
 					  rxrpc_propose_ack_retry_tx);
-		} else {
-			spin_lock_bh(&call->lock);
-			if (after(hard_ack, call->ackr_consumed))
-				call->ackr_consumed = hard_ack;
-			if (after(top, call->ackr_seen))
-				call->ackr_seen = top;
-			spin_unlock_bh(&call->lock);
 		}
 
 		rxrpc_set_keepalive(call);

net/rxrpc/recvmsg.c

@@ -260,11 +260,9 @@ static void rxrpc_rotate_rx_window(struct rxrpc_call *call)
 		rxrpc_end_rx_phase(call, serial);
 	} else {
 		/* Check to see if there's an ACK that needs sending. */
-		if (after_eq(hard_ack, call->ackr_consumed + 2) ||
-		    after_eq(top, call->ackr_seen + 2) ||
-		    (hard_ack == top && after(hard_ack, call->ackr_consumed)))
-			rxrpc_propose_ACK(call, RXRPC_ACK_DELAY, serial,
-					  true, true,
+		if (atomic_inc_return(&call->ackr_nr_consumed) > 2)
+			rxrpc_propose_ACK(call, RXRPC_ACK_IDLE, serial,
+					  true, false,
 					  rxrpc_propose_ack_rotate_rx);
 		if (call->ackr_reason && call->ackr_reason != RXRPC_ACK_DELAY)
 			rxrpc_send_ack_packet(call, false, NULL);