rxrpc: Calculate serial skew on packet reception

Calculate the serial number skew in the data_ready handler when a packet
has been received and a connection looked up.  The skew is cached in the
sk_buff's priority field.

The connection highest received serial number is updated at this time also.
This can be done without locks or atomic instructions because, at this
point, the code is serialised by the socket.

This generates more accurate skew data because if the packet is offloaded
to a work queue before this is determined, more packets may come in,
bumping the highest serial number and thereby increasing the apparent skew.

This also removes some unnecessary atomic ops.

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

1 files changed, 23 insertions, 14 deletions

diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 70bb77818dea..34f7431bf494 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -125,6 +125,7 @@ static int rxrpc_fast_process_data(struct rxrpc_call *call,
 	bool terminal;
 	int ret, ackbit, ack;
 	u32 serial;
+	u16 skew;
 	u8 flags;
 
 	_enter("{%u,%u},,{%u}", call->rx_data_post, call->rx_first_oos, seq);
@@ -133,6 +134,7 @@ static int rxrpc_fast_process_data(struct rxrpc_call *call,
 	ASSERTCMP(sp->call, ==, NULL);
 	flags = sp->hdr.flags;
 	serial = sp->hdr.serial;
+	skew = skb->priority;
 
 	spin_lock(&call->lock);
 
@@ -231,7 +233,7 @@ static int rxrpc_fast_process_data(struct rxrpc_call *call,
 
 	spin_unlock(&call->lock);
 	atomic_inc(&call->ackr_not_idle);
-	rxrpc_propose_ACK(call, RXRPC_ACK_DELAY, serial, false);
+	rxrpc_propose_ACK(call, RXRPC_ACK_DELAY, skew, serial, false);
 	_leave(" = 0 [posted]");
 	return 0;
 
@@ -244,7 +246,7 @@ out:
 
 discard_and_ack:
 	_debug("discard and ACK packet %p", skb);
-	__rxrpc_propose_ACK(call, ack, serial, true);
+	__rxrpc_propose_ACK(call, ack, skew, serial, true);
 discard:
 	spin_unlock(&call->lock);
 	rxrpc_free_skb(skb);
@@ -252,7 +254,7 @@ discard:
 	return 0;
 
 enqueue_and_ack:
-	__rxrpc_propose_ACK(call, ack, serial, true);
+	__rxrpc_propose_ACK(call, ack, skew, serial, true);
 enqueue_packet:
 	_net("defer skb %p", skb);
 	spin_unlock(&call->lock);
@@ -304,7 +306,7 @@ void rxrpc_fast_process_packet(struct rxrpc_call *call, struct sk_buff *skb)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	__be32 wtmp;
-	u32 hi_serial, abort_code;
+	u32 abort_code;
 
 	_enter("%p,%p", call, skb);
 
@@ -321,18 +323,12 @@ void rxrpc_fast_process_packet(struct rxrpc_call *call, struct sk_buff *skb)
 	}
 #endif
 
-	/* track the latest serial number on this connection for ACK packet
-	 * information */
-	hi_serial = atomic_read(&call->conn->hi_serial);
-	while (sp->hdr.serial > hi_serial)
-		hi_serial = atomic_cmpxchg(&call->conn->hi_serial, hi_serial,
-					   sp->hdr.serial);
-
 	/* request ACK generation for any ACK or DATA packet that requests
 	 * it */
 	if (sp->hdr.flags & RXRPC_REQUEST_ACK) {
 		_proto("ACK Requested on %%%u", sp->hdr.serial);
-		rxrpc_propose_ACK(call, RXRPC_ACK_REQUESTED, sp->hdr.serial, false);
+		rxrpc_propose_ACK(call, RXRPC_ACK_REQUESTED,
+				  skb->priority, sp->hdr.serial, false);
 	}
 
 	switch (sp->hdr.type) {
@@ -637,7 +633,7 @@ void rxrpc_data_ready(struct sock *sk)
 	struct rxrpc_skb_priv *sp;
 	struct rxrpc_local *local = sk->sk_user_data;
 	struct sk_buff *skb;
-	int ret;
+	int ret, skew;
 
 	_enter("%p", sk);
 
@@ -700,8 +696,21 @@ void rxrpc_data_ready(struct sock *sk)
 	rcu_read_lock();
 
 	conn = rxrpc_find_connection_rcu(local, skb);
-	if (!conn)
+	if (!conn) {
+		skb->priority = 0;
 		goto cant_route_call;
+	}
+
+	/* Note the serial number skew here */
+	skew = (int)sp->hdr.serial - (int)conn->hi_serial;
+	if (skew >= 0) {
+		if (skew > 0)
+			conn->hi_serial = sp->hdr.serial;
+		skb->priority = 0;
+	} else {
+		skew = -skew;
+		skb->priority = min(skew, 65535);
+	}
 
 	if (sp->hdr.callNumber == 0) {
 		/* Connection-level packet */