[dpdk-stable] [PATCH 20.11 2/2] net/hns3: fix stats flip overflow

[Huisong Li <lihuisong@huawei.com>]

From: Chengchang Tang <tangchengchang@huawei.com>

[ upstream commit c27e64ee3e9b4ae6c763a4f00f72927e80e2e5f2 ]

Currently, statistics may overflow in some scenarios.

For example, if HW statistics are reset by stats reset operation,
but there are still a lot of residual packets exist in the HW
queues and these packets are error packets, flip may occurred
because the ipacket is obtained by subtracting the number of
software error packets from the number of HW received packets.

This patch verifies the calculation and returns 0 when overflow
may occur.

Fixes: 8839c5e202f3 ("net/hns3: support device stats")

Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Lijun Ou <oulijun@huawei.com>
---
 drivers/net/hns3/hns3_stats.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/net/hns3/hns3_stats.c b/drivers/net/hns3/hns3_stats.c
index 62a712b..48ab6a3 100644
--- a/drivers/net/hns3/hns3_stats.c
+++ b/drivers/net/hns3/hns3_stats.c
@@ -521,8 +521,15 @@ hns3_stats_get(struct rte_eth_dev *eth_dev, struct rte_eth_stats *rte_stats)
 		if (rxq) {
 			cnt = rxq->l2_errors + rxq->pkt_len_errors;
 			rte_stats->q_errors[i] = cnt;
+			/*
+			 * If HW statistics are reset by stats_reset, but
+			 * a lot of residual packets exist in the hardware
+			 * queue and these packets are error packets, flip
+			 * overflow may occurred. So return 0 in this case.
+			 */
 			rte_stats->q_ipackets[i] =
-				stats->rcb_rx_ring_pktnum[i] - cnt;
+				stats->rcb_rx_ring_pktnum[i] > cnt ?
+				stats->rcb_rx_ring_pktnum[i] - cnt : 0;
 			rte_stats->ierrors += cnt;
 		}
 	}
@@ -535,8 +542,9 @@ hns3_stats_get(struct rte_eth_dev *eth_dev, struct rte_eth_stats *rte_stats)
 	}
 
 	rte_stats->oerrors = 0;
-	rte_stats->ipackets  = stats->rcb_rx_ring_pktnum_rcd -
-		rte_stats->ierrors;
+	rte_stats->ipackets =
+		stats->rcb_rx_ring_pktnum_rcd > rte_stats->ierrors ?
+		stats->rcb_rx_ring_pktnum_rcd - rte_stats->ierrors : 0;
 	rte_stats->opackets  = stats->rcb_tx_ring_pktnum_rcd -
 		rte_stats->oerrors;
 	rte_stats->rx_nombuf = eth_dev->data->rx_mbuf_alloc_failed;
-- 
2.8.1