patch 'net/ice: fix DCF Rx packets statistics underflow' has been queued to stable release 25.11.3

[Kevin Traynor]

Hi,

FYI, your patch has been queued to stable release 25.11.3

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 08/01/26. So please
shout if anyone has objections.

Also note that after the patch there's a diff of the upstream commit vs the
patch applied to the branch. This will indicate if there was any rebasing
needed to apply to the stable branch. If there were code changes for rebasing
(ie: not only metadata diffs), please double check that the rebase was
correctly done.

Queued patches are on a temporary branch at:
https://github.com/kevintraynor/dpdk-stable

This queued commit can be viewed at:
https://github.com/kevintraynor/dpdk-stable/commit/479af51bef59270723cc13cd648f68d1837d34ff

Thanks.

Kevin

---
>From 479af51bef59270723cc13cd648f68d1837d34ff Mon Sep 17 00:00:00 2001
From: Ciara Loftus <ciara.loftus at intel.com>
Date: Thu, 25 Jun 2026 09:36:18 +0000
Subject: [PATCH] net/ice: fix DCF Rx packets statistics underflow

[ upstream commit 7d9336433af621915eb574179564cee5de63c433 ]

The number of Rx packets is computed as the sum of the unicast,
multicast and broadcast packet counters, minus the discarded packet
count:

    ipackets = rx_unicast + rx_multicast + rx_broadcast - rx_discards

The unicast, multicast and broadcast counters already include the
packets that were subsequently dropped, so subtracting rx_discards
yields only the packets delivered to the application. These values are
provided by the PF in a virtchnl_eth_stats message; the PF samples them
from separate sources and the order in which they are read cannot be
guaranteed. Under load, rx_discards can therefore momentarily exceed the
sum of the unicast, multicast and broadcast counters. As ipackets is
unsigned, the subtraction then wraps to a huge bogus value, reported to
the application as an enormous Rx packet count and packet rate.

The read order cannot be guaranteed, so use a saturating subtraction:
when rx_discards exceeds the sum of the unicast, multicast and broadcast
counters essentially nothing was delivered, so report zero instead of
underflowing.

Fixes: c9f889e99616 ("net/ice: enable stats for DCF")

Signed-off-by: Ciara Loftus <ciara.loftus at intel.com>
Acked-by: Bruce Richardson <bruce.richardson at intel.com>
---
 drivers/net/intel/ice/ice_dcf_ethdev.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/net/intel/ice/ice_dcf_ethdev.c b/drivers/net/intel/ice/ice_dcf_ethdev.c
index 81da5a4656..1d8b73d957 100644
--- a/drivers/net/intel/ice/ice_dcf_ethdev.c
+++ b/drivers/net/intel/ice/ice_dcf_ethdev.c
@@ -1532,6 +1532,14 @@ ice_dcf_stats_get(struct rte_eth_dev *dev, struct rte_eth_stats *stats,
 	if (ret == 0) {
 		ice_dcf_update_stats(&hw->eth_stats_offset, &pstats);
-		stats->ipackets = pstats.rx_unicast + pstats.rx_multicast +
-				pstats.rx_broadcast - pstats.rx_discards;
+		stats->ipackets = pstats.rx_unicast + pstats.rx_multicast + pstats.rx_broadcast;
+		/*
+		 * Unicast/multicast/broadcast counters include discarded packets, so subtract
+		 * rx_discards to report only the packets delivered to the application. The
+		 * counters are sampled from separate sources and can be momentarily inconsistent
+		 * under load. If rx_discards exceeds their sum then essentially nothing was
+		 * delivered, so saturate at zero rather than underflow.
+		 */
+		stats->ipackets = stats->ipackets >= pstats.rx_discards ?
+					stats->ipackets - pstats.rx_discards : 0;
 		stats->opackets = pstats.tx_broadcast + pstats.tx_multicast +
 						pstats.tx_unicast;
-- 
2.55.0

---
  Diff of the applied patch vs upstream commit (please double-check if non-empty:
---
--- -	2026-07-28 16:54:52.844433925 +0100
+++ 0070-net-ice-fix-DCF-Rx-packets-statistics-underflow.patch	2026-07-28 16:54:50.828728976 +0100
@@ -1 +1 @@
-From 7d9336433af621915eb574179564cee5de63c433 Mon Sep 17 00:00:00 2001
+From 479af51bef59270723cc13cd648f68d1837d34ff Mon Sep 17 00:00:00 2001
@@ -5,0 +6,2 @@
+[ upstream commit 7d9336433af621915eb574179564cee5de63c433 ]
+
@@ -28 +29,0 @@
-Cc: stable at dpdk.org
@@ -37 +38 @@
-index 4fce59617e..c78b290b0d 100644
+index 81da5a4656..1d8b73d957 100644
@@ -40 +41 @@
-@@ -1524,6 +1524,14 @@ ice_dcf_stats_get(struct rte_eth_dev *dev, struct rte_eth_stats *stats,
+@@ -1532,6 +1532,14 @@ ice_dcf_stats_get(struct rte_eth_dev *dev, struct rte_eth_stats *stats,