Merge branch 'sctp-pmtud-convergence'

Xin Long says:

====================
sctp: make the PLPMTUD probe more effective and efficient

As David Laight noticed, it currently takes quite some time to find
the optimal pmtu in the Search state, and also lacks the black hole
detection in the Search Complete state. This patchset is to address
them to mke the PLPMTUD probe more effective and efficient.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.rst

@@ -2835,10 +2835,14 @@ encap_port - INTEGER
 	Default: 0
 
 plpmtud_probe_interval - INTEGER
-        The time interval (in milliseconds) for sending PLPMTUD probe chunks.
-        These chunks are sent at the specified interval with a variable size
-        to probe the mtu of a given path between 2 endpoints. PLPMTUD will
-        be disabled when 0 is set, and other values for it must be >= 5000.
+        The time interval (in milliseconds) for the PLPMTUD probe timer,
+        which is configured to expire after this period to receive an
+        acknowledgment to a probe packet. This is also the time interval
+        between the probes for the current pmtu when the probe search
+        is done.
+
+        PLPMTUD will be disabled when 0 is set, and other values for it
+        must be >= 5000.
 
 	Default: 0
 

include/net/sctp/structs.h

@@ -987,7 +987,8 @@ struct sctp_transport {
 		__u16 pmtu;
 		__u16 probe_size;
 		__u16 probe_high;
-		__u8 probe_count;
+		__u8 probe_count:3;
+		__u8 raise_count:5;
 		__u8 state;
 	} pl; /* plpmtud related */
 

net/sctp/sm_statefuns.c

@@ -1275,7 +1275,10 @@ enum sctp_disposition sctp_sf_backbeat_8_3(struct net *net,
 			return SCTP_DISPOSITION_DISCARD;
 
 		sctp_transport_pl_recv(link);
+		if (link->pl.state == SCTP_PL_COMPLETE)
 			return SCTP_DISPOSITION_CONSUME;
+
+		return sctp_sf_send_probe(net, ep, asoc, type, link, commands);
 	}
 
 	max_interval = link->hbinterval + link->rto;

net/sctp/transport.c

@@ -213,15 +213,10 @@ void sctp_transport_reset_reconf_timer(struct sctp_transport *transport)
 
 void sctp_transport_reset_probe_timer(struct sctp_transport *transport)
 {
-	int scale = 1;
-
 	if (timer_pending(&transport->probe_timer))
 		return;
-	if (transport->pl.state == SCTP_PL_COMPLETE &&
-	    transport->pl.probe_count == 1)
-		scale = 30; /* works as PMTU_RAISE_TIMER */
 	if (!mod_timer(&transport->probe_timer,
-		       jiffies + transport->probe_interval * scale))
+		       jiffies + transport->probe_interval))
 		sctp_transport_hold(transport);
 }
 
@@ -333,13 +328,15 @@ void sctp_transport_pl_recv(struct sctp_transport *t)
 		t->pl.probe_size += SCTP_PL_MIN_STEP;
 		if (t->pl.probe_size >= t->pl.probe_high) {
 			t->pl.probe_high = 0;
+			t->pl.raise_count = 0;
 			t->pl.state = SCTP_PL_COMPLETE; /* Search -> Search Complete */
 
 			t->pl.probe_size = t->pl.pmtu;
 			t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t);
 			sctp_assoc_sync_pmtu(t->asoc);
 		}
-	} else if (t->pl.state == SCTP_PL_COMPLETE) {
+	} else if (t->pl.state == SCTP_PL_COMPLETE && ++t->pl.raise_count == 30) {
+		/* Raise probe_size again after 30 * interval in Search Complete */
 		t->pl.state = SCTP_PL_SEARCH; /* Search Complete -> Search */
 		t->pl.probe_size += SCTP_PL_MIN_STEP;
 	}