[PATCH net-next 14/37] rxrpc: Only set DF=1 on initial DATA transmission

[David Howells <dhowells@redhat.com>]

Change how the DF flag is managed on DATA transmissions.  Set it on initial
transmission and don't set it on retransmissions.  Then remove the handling
for EMSGSIZE in rxrpc_send_data_packet() and just pretend it didn't happen,
leaving it to the retransmission path to retry.

The path-MTU discovery using PING ACKs is then used to probe for the
maximum DATA size - though notification by ICMP will be used if one is
received.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
---
 net/rxrpc/ar-internal.h |  1 +
 net/rxrpc/output.c      | 32 ++++++++++++++++----------------
 net/rxrpc/proc.c        |  5 +++--
 3 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 55cc68dd1b40..84efa21f176c 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -98,6 +98,7 @@ struct rxrpc_net {
 	atomic_t		stat_tx_data_send;
 	atomic_t		stat_tx_data_send_frag;
 	atomic_t		stat_tx_data_send_fail;
+	atomic_t		stat_tx_data_send_msgsize;
 	atomic_t		stat_tx_data_underflow;
 	atomic_t		stat_tx_data_cwnd_reset;
 	atomic_t		stat_rx_data;
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 56695c441514..95a3819dd85d 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -551,16 +551,11 @@ static int rxrpc_send_data_packet(struct rxrpc_call *call, struct rxrpc_txbuf *t
 	msg.msg_controllen = 0;
 	msg.msg_flags	= MSG_SPLICE_PAGES;
 
-	/* Track what we've attempted to transmit at least once so that the
-	 * retransmission algorithm doesn't try to resend what we haven't sent
-	 * yet.
+	/* Send the packet with the don't fragment bit set unless we think it's
+	 * too big or if this is a retransmission.
 	 */
-	if (txb->seq == call->tx_transmitted + 1)
-		call->tx_transmitted = txb->seq + n - 1;
-
-	/* send the packet with the don't fragment bit set if we currently
-	 * think it's small enough */
-	if (len >= sizeof(struct rxrpc_wire_header) + call->peer->max_data) {
+	if (txb->seq == call->tx_transmitted + 1 &&
+	    len >= sizeof(struct rxrpc_wire_header) + call->peer->max_data) {
 		rxrpc_local_dont_fragment(conn->local, false);
 		frag = rxrpc_tx_point_call_data_frag;
 	} else {
@@ -568,6 +563,13 @@ static int rxrpc_send_data_packet(struct rxrpc_call *call, struct rxrpc_txbuf *t
 		frag = rxrpc_tx_point_call_data_nofrag;
 	}
 
+	/* Track what we've attempted to transmit at least once so that the
+	 * retransmission algorithm doesn't try to resend what we haven't sent
+	 * yet.
+	 */
+	if (txb->seq == call->tx_transmitted + 1)
+		call->tx_transmitted = txb->seq + n - 1;
+
 	if (IS_ENABLED(CONFIG_AF_RXRPC_INJECT_LOSS)) {
 		static int lose;
 		if ((lose++ & 7) == 7) {
@@ -578,7 +580,6 @@ static int rxrpc_send_data_packet(struct rxrpc_call *call, struct rxrpc_txbuf *t
 		}
 	}
 
-retry:
 	/* send the packet by UDP
 	 * - returns -EMSGSIZE if UDP would have to fragment the packet
 	 *   to go out of the interface
@@ -589,7 +590,11 @@ static int rxrpc_send_data_packet(struct rxrpc_call *call, struct rxrpc_txbuf *t
 	ret = do_udp_sendmsg(conn->local->socket, &msg, len);
 	conn->peer->last_tx_at = ktime_get_seconds();
 
-	if (ret < 0) {
+	if (ret == -EMSGSIZE) {
+		rxrpc_inc_stat(call->rxnet, stat_tx_data_send_msgsize);
+		trace_rxrpc_tx_packet(call->debug_id, call->local->kvec[0].iov_base, frag);
+		ret = 0;
+	} else if (ret < 0) {
 		rxrpc_inc_stat(call->rxnet, stat_tx_data_send_fail);
 		trace_rxrpc_tx_fail(call->debug_id, txb->serial, ret, frag);
 	} else {
@@ -597,11 +602,6 @@ static int rxrpc_send_data_packet(struct rxrpc_call *call, struct rxrpc_txbuf *t
 	}
 
 	rxrpc_tx_backoff(call, ret);
-	if (ret == -EMSGSIZE && frag == rxrpc_tx_point_call_data_nofrag) {
-		rxrpc_local_dont_fragment(conn->local, false);
-		frag = rxrpc_tx_point_call_data_frag;
-		goto retry;
-	}
 
 done:
 	if (ret >= 0) {
diff --git a/net/rxrpc/proc.c b/net/rxrpc/proc.c
index 1f1387cf62c8..aab392b4281f 100644
--- a/net/rxrpc/proc.c
+++ b/net/rxrpc/proc.c
@@ -476,10 +476,11 @@ int rxrpc_stats_show(struct seq_file *seq, void *v)
 	struct rxrpc_net *rxnet = rxrpc_net(seq_file_single_net(seq));
 
 	seq_printf(seq,
-		   "Data     : send=%u sendf=%u fail=%u\n",
+		   "Data     : send=%u sendf=%u fail=%u emsz=%u\n",
 		   atomic_read(&rxnet->stat_tx_data_send),
 		   atomic_read(&rxnet->stat_tx_data_send_frag),
-		   atomic_read(&rxnet->stat_tx_data_send_fail));
+		   atomic_read(&rxnet->stat_tx_data_send_fail),
+		   atomic_read(&rxnet->stat_tx_data_send_msgsize));
 	seq_printf(seq,
 		   "Data-Tx  : nr=%u retrans=%u uf=%u cwr=%u\n",
 		   atomic_read(&rxnet->stat_tx_data),