[PATCH 6.19 73/86] rxrpc: Fix to request an ack if window is limited

[Greg Kroah-Hartman]

6.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Marc Dionne <marc.c.dionne at gmail.com>

commit 0cd3e3f3f2ec1a45aa559e2c0f3d57fac5eb3c25 upstream.

Peers may only send immediate acks for every 2 UDP packets received.
When sending a jumbogram, it is important to check that there is
sufficient window space to send another same sized jumbogram following
the current one, and request an ack if there isn't.  Failure to do so may
cause the call to stall waiting for an ack until the resend timer fires.

Where jumbograms are in use this causes a very significant drop in
performance.

Fixes: fe24a5494390 ("rxrpc: Send jumbo DATA packets")
Signed-off-by: Marc Dionne <marc.dionne at auristor.com>
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Jeffrey Altman <jaltman at auristor.com>
cc: Simon Horman <horms at kernel.org>
cc: linux-afs at lists.infradead.org
cc: stable at kernel.org
Link: https://patch.msgid.link/20260408121252.2249051-10-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 include/trace/events/rxrpc.h |    1 +
 net/rxrpc/ar-internal.h      |    2 +-
 net/rxrpc/output.c           |    2 ++
 net/rxrpc/proc.c             |    5 +++--
 4 files changed, 7 insertions(+), 3 deletions(-)

--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -521,6 +521,7 @@
 #define rxrpc_req_ack_traces \
 	EM(rxrpc_reqack_ack_lost,		"ACK-LOST  ")	\
 	EM(rxrpc_reqack_app_stall,		"APP-STALL ")	\
+	EM(rxrpc_reqack_jumbo_win,		"JUMBO-WIN ")	\
 	EM(rxrpc_reqack_more_rtt,		"MORE-RTT  ")	\
 	EM(rxrpc_reqack_no_srv_last,		"NO-SRVLAST")	\
 	EM(rxrpc_reqack_old_rtt,		"OLD-RTT   ")	\
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -117,7 +117,7 @@ struct rxrpc_net {
 	atomic_t		stat_tx_jumbo[10];
 	atomic_t		stat_rx_jumbo[10];
 
-	atomic_t		stat_why_req_ack[8];
+	atomic_t		stat_why_req_ack[9];
 
 	atomic_t		stat_io_loop;
 };
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -479,6 +479,8 @@ static size_t rxrpc_prepare_data_subpack
 		why = rxrpc_reqack_old_rtt;
 	else if (!last && !after(READ_ONCE(call->send_top), txb->seq))
 		why = rxrpc_reqack_app_stall;
+	else if (call->tx_winsize <= (2 * req->n) || call->cong_cwnd <= (2 * req->n))
+		why = rxrpc_reqack_jumbo_win;
 	else
 		goto dont_set_request_ack;
 
--- a/net/rxrpc/proc.c
+++ b/net/rxrpc/proc.c
@@ -518,11 +518,12 @@ int rxrpc_stats_show(struct seq_file *se
 		   atomic_read(&rxnet->stat_rx_acks[RXRPC_ACK_IDLE]),
 		   atomic_read(&rxnet->stat_rx_acks[0]));
 	seq_printf(seq,
-		   "Why-Req-A: acklost=%u mrtt=%u ortt=%u stall=%u\n",
+		   "Why-Req-A: acklost=%u mrtt=%u ortt=%u stall=%u jwin=%u\n",
 		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_ack_lost]),
 		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_more_rtt]),
 		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_old_rtt]),
-		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_app_stall]));
+		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_app_stall]),
+		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_jumbo_win]));
 	seq_printf(seq,
 		   "Why-Req-A: nolast=%u retx=%u slows=%u smtxw=%u\n",
 		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_no_srv_last]),