Merge tag 'rxrpc-fixes-20200520' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

David Howells says:

====================
rxrpc: Fix retransmission timeout and ACK discard

Here are a couple of fixes and an extra tracepoint for AF_RXRPC:

 (1) Calculate the RTO pretty much as TCP does, rather than making
     something up, including an initial 4s timeout (which causes return
     probes from the fileserver to fail if a packet goes missing), and add
     backoff.

 (2) Fix the discarding of out-of-order received ACKs.  We mustn't let the
     hard-ACK point regress, nor do we want to do unnecessary
     retransmission because the soft-ACK list regresses.  This is not
     trivial, however, due to some loose wording in various old protocol
     specs, the ACK field that should be used for this sometimes has the
     wrong information in it.

 (3) Add a tracepoint to log a discarded ACK.
====================

Signed-off-by: David S. Miller <[email protected]>

Author: davem330

fs/afs/fs_probe.c

@@ -32,9 +32,8 @@ void afs_fileserver_probe_result(struct afs_call *call)
 	struct afs_server *server = call->server;
 	unsigned int server_index = call->server_index;
 	unsigned int index = call->addr_ix;
-	unsigned int rtt = UINT_MAX;
+	unsigned int rtt_us;
 	bool have_result = false;
-	u64 _rtt;
 	int ret = call->error;
 
 	_enter("%pU,%u", &server->uuid, index);
@@ -93,15 +92,9 @@ void afs_fileserver_probe_result(struct afs_call *call)
 		}
 	}
 
-	/* Get the RTT and scale it to fit into a 32-bit value that represents
-	 * over a minute of time so that we can access it with one instruction
-	 * on a 32-bit system.
-	 */
-	_rtt = rxrpc_kernel_get_rtt(call->net->socket, call->rxcall);
-	_rtt /= 64;
-	rtt = (_rtt > UINT_MAX) ? UINT_MAX : _rtt;
-	if (rtt < server->probe.rtt) {
-		server->probe.rtt = rtt;
+	rtt_us = rxrpc_kernel_get_srtt(call->net->socket, call->rxcall);
+	if (rtt_us < server->probe.rtt) {
+		server->probe.rtt = rtt_us;
 		alist->preferred = index;
 		have_result = true;
 	}
@@ -113,8 +106,7 @@ void afs_fileserver_probe_result(struct afs_call *call)
 	spin_unlock(&server->probe_lock);
 
 	_debug("probe [%u][%u] %pISpc rtt=%u ret=%d",
-	       server_index, index, &alist->addrs[index].transport,
-	       (unsigned int)rtt, ret);
+	       server_index, index, &alist->addrs[index].transport, rtt_us, ret);
 
 	have_result |= afs_fs_probe_done(server);
 	if (have_result)

fs/afs/vl_probe.c

@@ -31,10 +31,9 @@ void afs_vlserver_probe_result(struct afs_call *call)
 	struct afs_addr_list *alist = call->alist;
 	struct afs_vlserver *server = call->vlserver;
 	unsigned int server_index = call->server_index;
+	unsigned int rtt_us = 0;
 	unsigned int index = call->addr_ix;
-	unsigned int rtt = UINT_MAX;
 	bool have_result = false;
-	u64 _rtt;
 	int ret = call->error;
 
 	_enter("%s,%u,%u,%d,%d", server->name, server_index, index, ret, call->abort_code);
@@ -93,15 +92,9 @@ void afs_vlserver_probe_result(struct afs_call *call)
 		}
 	}
 
-	/* Get the RTT and scale it to fit into a 32-bit value that represents
-	 * over a minute of time so that we can access it with one instruction
-	 * on a 32-bit system.
-	 */
-	_rtt = rxrpc_kernel_get_rtt(call->net->socket, call->rxcall);
-	_rtt /= 64;
-	rtt = (_rtt > UINT_MAX) ? UINT_MAX : _rtt;
-	if (rtt < server->probe.rtt) {
-		server->probe.rtt = rtt;
+	rtt_us = rxrpc_kernel_get_srtt(call->net->socket, call->rxcall);
+	if (rtt_us < server->probe.rtt) {
+		server->probe.rtt = rtt_us;
 		alist->preferred = index;
 		have_result = true;
 	}
@@ -113,8 +106,7 @@ void afs_vlserver_probe_result(struct afs_call *call)
 	spin_unlock(&server->probe_lock);
 
 	_debug("probe [%u][%u] %pISpc rtt=%u ret=%d",
-	       server_index, index, &alist->addrs[index].transport,
-	       (unsigned int)rtt, ret);
+	       server_index, index, &alist->addrs[index].transport, rtt_us, ret);
 
 	have_result |= afs_vl_probe_done(server);
 	if (have_result) {

include/net/af_rxrpc.h

@@ -59,7 +59,7 @@ bool rxrpc_kernel_abort_call(struct socket *, struct rxrpc_call *,
 void rxrpc_kernel_end_call(struct socket *, struct rxrpc_call *);
 void rxrpc_kernel_get_peer(struct socket *, struct rxrpc_call *,
 			   struct sockaddr_rxrpc *);
-u64 rxrpc_kernel_get_rtt(struct socket *, struct rxrpc_call *);
+u32 rxrpc_kernel_get_srtt(struct socket *, struct rxrpc_call *);
 int rxrpc_kernel_charge_accept(struct socket *, rxrpc_notify_rx_t,
 			       rxrpc_user_attach_call_t, unsigned long, gfp_t,
 			       unsigned int);

include/trace/events/rxrpc.h

@@ -1112,18 +1112,17 @@ TRACE_EVENT(rxrpc_rtt_tx,
 TRACE_EVENT(rxrpc_rtt_rx,
 	    TP_PROTO(struct rxrpc_call *call, enum rxrpc_rtt_rx_trace why,
 		     rxrpc_serial_t send_serial, rxrpc_serial_t resp_serial,
-		     s64 rtt, u8 nr, s64 avg),
+		     u32 rtt, u32 rto),
 
-	    TP_ARGS(call, why, send_serial, resp_serial, rtt, nr, avg),
+	    TP_ARGS(call, why, send_serial, resp_serial, rtt, rto),
 
 	    TP_STRUCT__entry(
 		    __field(unsigned int,		call		)
 		    __field(enum rxrpc_rtt_rx_trace,	why		)
-		    __field(u8,				nr		)
 		    __field(rxrpc_serial_t,		send_serial	)
 		    __field(rxrpc_serial_t,		resp_serial	)
-		    __field(s64,			rtt		)
-		    __field(u64,			avg		)
+		    __field(u32,			rtt		)
+		    __field(u32,			rto		)
 			     ),
 
 	    TP_fast_assign(
@@ -1132,18 +1131,16 @@ TRACE_EVENT(rxrpc_rtt_rx,
 		    __entry->send_serial = send_serial;
 		    __entry->resp_serial = resp_serial;
 		    __entry->rtt = rtt;
-		    __entry->nr = nr;
-		    __entry->avg = avg;
+		    __entry->rto = rto;
 			   ),
 
-	    TP_printk("c=%08x %s sr=%08x rr=%08x rtt=%lld nr=%u avg=%lld",
+	    TP_printk("c=%08x %s sr=%08x rr=%08x rtt=%u rto=%u",
 		      __entry->call,
 		      __print_symbolic(__entry->why, rxrpc_rtt_rx_traces),
 		      __entry->send_serial,
 		      __entry->resp_serial,
 		      __entry->rtt,
-		      __entry->nr,
-		      __entry->avg)
+		      __entry->rto)
 	    );
 
 TRACE_EVENT(rxrpc_timer,
@@ -1544,6 +1541,41 @@ TRACE_EVENT(rxrpc_notify_socket,
 		      __entry->serial)
 	    );
 
+TRACE_EVENT(rxrpc_rx_discard_ack,
+	    TP_PROTO(unsigned int debug_id, rxrpc_serial_t serial,
+		     rxrpc_seq_t first_soft_ack, rxrpc_seq_t call_ackr_first,
+		     rxrpc_seq_t prev_pkt, rxrpc_seq_t call_ackr_prev),
+
+	    TP_ARGS(debug_id, serial, first_soft_ack, call_ackr_first,
+		    prev_pkt, call_ackr_prev),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,	debug_id	)
+		    __field(rxrpc_serial_t,	serial		)
+		    __field(rxrpc_seq_t,	first_soft_ack)
+		    __field(rxrpc_seq_t,	call_ackr_first)
+		    __field(rxrpc_seq_t,	prev_pkt)
+		    __field(rxrpc_seq_t,	call_ackr_prev)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->debug_id		= debug_id;
+		    __entry->serial		= serial;
+		    __entry->first_soft_ack	= first_soft_ack;
+		    __entry->call_ackr_first	= call_ackr_first;
+		    __entry->prev_pkt		= prev_pkt;
+		    __entry->call_ackr_prev	= call_ackr_prev;
+			   ),
+
+	    TP_printk("c=%08x r=%08x %08x<%08x %08x<%08x",
+		      __entry->debug_id,
+		      __entry->serial,
+		      __entry->first_soft_ack,
+		      __entry->call_ackr_first,
+		      __entry->prev_pkt,
+		      __entry->call_ackr_prev)
+	    );
+
 #endif /* _TRACE_RXRPC_H */
 
 /* This part must be outside protection */

net/rxrpc/Makefile

@@ -25,6 +25,7 @@ rxrpc-y := \
 	peer_event.o \
 	peer_object.o \
 	recvmsg.o \
+	rtt.o \
 	security.o \
 	sendmsg.o \
 	skbuff.o \

net/rxrpc/ar-internal.h

@@ -7,6 +7,7 @@
 
 #include <linux/atomic.h>
 #include <linux/seqlock.h>
+#include <linux/win_minmax.h>
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <net/sock.h>
@@ -311,11 +312,14 @@ struct rxrpc_peer {
 #define RXRPC_RTT_CACHE_SIZE 32
 	spinlock_t		rtt_input_lock;	/* RTT lock for input routine */
 	ktime_t			rtt_last_req;	/* Time of last RTT request */
-	u64			rtt;		/* Current RTT estimate (in nS) */
-	u64			rtt_sum;	/* Sum of cache contents */
-	u64			rtt_cache[RXRPC_RTT_CACHE_SIZE]; /* Determined RTT cache */
-	u8			rtt_cursor;	/* next entry at which to insert */
-	u8			rtt_usage;	/* amount of cache actually used */
+	unsigned int		rtt_count;	/* Number of samples we've got */
+
+	u32			srtt_us;	/* smoothed round trip time << 3 in usecs */
+	u32			mdev_us;	/* medium deviation			*/
+	u32			mdev_max_us;	/* maximal mdev for the last rtt period	*/
+	u32			rttvar_us;	/* smoothed mdev_max			*/
+	u32			rto_j;		/* Retransmission timeout in jiffies */
+	u8			backoff;	/* Backoff timeout */
 
 	u8			cong_cwnd;	/* Congestion window size */
 };
@@ -1041,7 +1045,6 @@ extern unsigned long rxrpc_idle_ack_delay;
 extern unsigned int rxrpc_rx_window_size;
 extern unsigned int rxrpc_rx_mtu;
 extern unsigned int rxrpc_rx_jumbo_max;
-extern unsigned long rxrpc_resend_timeout;
 
 extern const s8 rxrpc_ack_priority[];
 
@@ -1069,8 +1072,6 @@ void rxrpc_send_keepalive(struct rxrpc_peer *);
  * peer_event.c
  */
 void rxrpc_error_report(struct sock *);
-void rxrpc_peer_add_rtt(struct rxrpc_call *, enum rxrpc_rtt_rx_trace,
-			rxrpc_serial_t, rxrpc_serial_t, ktime_t, ktime_t);
 void rxrpc_peer_keepalive_worker(struct work_struct *);
 
 /*
@@ -1102,6 +1103,14 @@ extern const struct seq_operations rxrpc_peer_seq_ops;
 void rxrpc_notify_socket(struct rxrpc_call *);
 int rxrpc_recvmsg(struct socket *, struct msghdr *, size_t, int);
 
+/*
+ * rtt.c
+ */
+void rxrpc_peer_add_rtt(struct rxrpc_call *, enum rxrpc_rtt_rx_trace,
+			rxrpc_serial_t, rxrpc_serial_t, ktime_t, ktime_t);
+unsigned long rxrpc_get_rto_backoff(struct rxrpc_peer *, bool);
+void rxrpc_peer_init_rtt(struct rxrpc_peer *);
+
 /*
  * rxkad.c
  */

net/rxrpc/call_accept.c

@@ -248,7 +248,7 @@ static void rxrpc_send_ping(struct rxrpc_call *call, struct sk_buff *skb)
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	ktime_t now = skb->tstamp;
 
-	if (call->peer->rtt_usage < 3 ||
+	if (call->peer->rtt_count < 3 ||
 	    ktime_before(ktime_add_ms(call->peer->rtt_last_req, 1000), now))
 		rxrpc_propose_ACK(call, RXRPC_ACK_PING, sp->hdr.serial,
 				  true, true,

net/rxrpc/call_event.c

@@ -111,8 +111,8 @@ static void __rxrpc_propose_ACK(struct rxrpc_call *call, u8 ack_reason,
 	} else {
 		unsigned long now = jiffies, ack_at;
 
-		if (call->peer->rtt_usage > 0)
-			ack_at = nsecs_to_jiffies(call->peer->rtt);
+		if (call->peer->srtt_us != 0)
+			ack_at = usecs_to_jiffies(call->peer->srtt_us >> 3);
 		else
 			ack_at = expiry;
 
@@ -157,24 +157,18 @@ static void rxrpc_congestion_timeout(struct rxrpc_call *call)
 static void rxrpc_resend(struct rxrpc_call *call, unsigned long now_j)
 {
 	struct sk_buff *skb;
-	unsigned long resend_at;
+	unsigned long resend_at, rto_j;
 	rxrpc_seq_t cursor, seq, top;
-	ktime_t now, max_age, oldest, ack_ts, timeout, min_timeo;
+	ktime_t now, max_age, oldest, ack_ts;
 	int ix;
 	u8 annotation, anno_type, retrans = 0, unacked = 0;
 
 	_enter("{%d,%d}", call->tx_hard_ack, call->tx_top);
 
-	if (call->peer->rtt_usage > 1)
-		timeout = ns_to_ktime(call->peer->rtt * 3 / 2);
-	else
-		timeout = ms_to_ktime(rxrpc_resend_timeout);
-	min_timeo = ns_to_ktime((1000000000 / HZ) * 4);
-	if (ktime_before(timeout, min_timeo))
-		timeout = min_timeo;
+	rto_j = call->peer->rto_j;
 
 	now = ktime_get_real();
-	max_age = ktime_sub(now, timeout);
+	max_age = ktime_sub(now, jiffies_to_usecs(rto_j));
 
 	spin_lock_bh(&call->lock);
 
@@ -219,7 +213,7 @@ static void rxrpc_resend(struct rxrpc_call *call, unsigned long now_j)
 	}
 
 	resend_at = nsecs_to_jiffies(ktime_to_ns(ktime_sub(now, oldest)));
-	resend_at += jiffies + rxrpc_resend_timeout;
+	resend_at += jiffies + rto_j;
 	WRITE_ONCE(call->resend_at, resend_at);
 
 	if (unacked)
@@ -234,7 +228,7 @@ static void rxrpc_resend(struct rxrpc_call *call, unsigned long now_j)
 					rxrpc_timer_set_for_resend);
 		spin_unlock_bh(&call->lock);
 		ack_ts = ktime_sub(now, call->acks_latest_ts);
-		if (ktime_to_ns(ack_ts) < call->peer->rtt)
+		if (ktime_to_us(ack_ts) < (call->peer->srtt_us >> 3))
 			goto out;
 		rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, true, false,
 				  rxrpc_propose_ack_ping_for_lost_ack);

net/rxrpc/input.c

@@ -91,11 +91,11 @@ static void rxrpc_congestion_management(struct rxrpc_call *call,
 		/* We analyse the number of packets that get ACK'd per RTT
 		 * period and increase the window if we managed to fill it.
 		 */
-		if (call->peer->rtt_usage == 0)
+		if (call->peer->rtt_count == 0)
 			goto out;
 		if (ktime_before(skb->tstamp,
-				 ktime_add_ns(call->cong_tstamp,
-					      call->peer->rtt)))
+				 ktime_add_us(call->cong_tstamp,
+					      call->peer->srtt_us >> 3)))
 			goto out_no_clear_ca;
 		change = rxrpc_cong_rtt_window_end;
 		call->cong_tstamp = skb->tstamp;
@@ -802,6 +802,30 @@ static void rxrpc_input_soft_acks(struct rxrpc_call *call, u8 *acks,
 	}
 }
 
+/*
+ * Return true if the ACK is valid - ie. it doesn't appear to have regressed
+ * with respect to the ack state conveyed by preceding ACKs.
+ */
+static bool rxrpc_is_ack_valid(struct rxrpc_call *call,
+			       rxrpc_seq_t first_pkt, rxrpc_seq_t prev_pkt)
+{
+	rxrpc_seq_t base = READ_ONCE(call->ackr_first_seq);
+
+	if (after(first_pkt, base))
+		return true; /* The window advanced */
+
+	if (before(first_pkt, base))
+		return false; /* firstPacket regressed */
+
+	if (after_eq(prev_pkt, call->ackr_prev_seq))
+		return true; /* previousPacket hasn't regressed. */
+
+	/* Some rx implementations put a serial number in previousPacket. */
+	if (after_eq(prev_pkt, base + call->tx_winsize))
+		return false;
+	return true;
+}
+
 /*
  * Process an ACK packet.
  *
@@ -865,9 +889,12 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb)
 	}
 
 	/* Discard any out-of-order or duplicate ACKs (outside lock). */
-	if (before(first_soft_ack, call->ackr_first_seq) ||
-	    before(prev_pkt, call->ackr_prev_seq))
+	if (!rxrpc_is_ack_valid(call, first_soft_ack, prev_pkt)) {
+		trace_rxrpc_rx_discard_ack(call->debug_id, sp->hdr.serial,
+					   first_soft_ack, call->ackr_first_seq,
+					   prev_pkt, call->ackr_prev_seq);
 		return;
+	}
 
 	buf.info.rxMTU = 0;
 	ioffset = offset + nr_acks + 3;
@@ -878,9 +905,12 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb)
 	spin_lock(&call->input_lock);
 
 	/* Discard any out-of-order or duplicate ACKs (inside lock). */
-	if (before(first_soft_ack, call->ackr_first_seq) ||
-	    before(prev_pkt, call->ackr_prev_seq))
+	if (!rxrpc_is_ack_valid(call, first_soft_ack, prev_pkt)) {
+		trace_rxrpc_rx_discard_ack(call->debug_id, sp->hdr.serial,
+					   first_soft_ack, call->ackr_first_seq,
+					   prev_pkt, call->ackr_prev_seq);
 		goto out;
+	}
 	call->acks_latest_ts = skb->tstamp;
 
 	call->ackr_first_seq = first_soft_ack;

net/rxrpc/misc.c

@@ -63,11 +63,6 @@ unsigned int rxrpc_rx_mtu = 5692;
  */
 unsigned int rxrpc_rx_jumbo_max = 4;
 
-/*
- * Time till packet resend (in milliseconds).
- */
-unsigned long rxrpc_resend_timeout = 4 * HZ;
-
 const s8 rxrpc_ack_priority[] = {
 	[0]				= 0,
 	[RXRPC_ACK_DELAY]		= 1,