linux-kernel - [PATCH V3 net 2/3] net: hibmcge: fix the division by zero issue

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Message-ID: <20250806102758.3632674-3-shaojijie@huawei.com>
Date: Wed, 6 Aug 2025 18:27:57 +0800
From: Jijie Shao <shaojijie@...wei.com>
To: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <andrew+netdev@...n.ch>, <horms@...nel.org>
CC: <shenjian15@...wei.com>, <liuyonglong@...wei.com>,
	<chenhao418@...wei.com>, <jonathan.cameron@...wei.com>,
	<shameerali.kolothum.thodi@...wei.com>, <salil.mehta@...wei.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<shaojijie@...wei.com>
Subject: [PATCH V3 net 2/3] net: hibmcge: fix the division by zero issue

When the network port is down, the queue is released, and ring->len is 0.
In debugfs, hbg_get_queue_used_num() will be called,
which may lead to a division by zero issue.

This patch adds a check, if ring->len is 0,
hbg_get_queue_used_num() directly returns 0.

Fixes: 40735e7543f9 ("net: hibmcge: Implement .ndo_start_xmit function")
Signed-off-by: Jijie Shao <shaojijie@...wei.com>
Reviewed-by: Simon Horman <horms@...nel.org>
---
ChangeLog:
v2 -> v3:
  - Use READ_ONCE() to read temporary variable, suggested by Jakub Kicinski
  v2: https://lore.kernel.org/all/20250805181446.3deaceb9@kernel.org/
---
 drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.h b/drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.h
index 2883a5899ae2..8b6110599e10 100644
--- a/drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.h
+++ b/drivers/net/ethernet/hisilicon/hibmcge/hbg_txrx.h
@@ -29,7 +29,12 @@ static inline bool hbg_fifo_is_full(struct hbg_priv *priv, enum hbg_dir dir)
 
 static inline u32 hbg_get_queue_used_num(struct hbg_ring *ring)
 {
-	return (ring->ntu + ring->len - ring->ntc) % ring->len;
+	u32 len = READ_ONCE(ring->len);
+
+	if (!len)
+		return 0;
+
+	return (READ_ONCE(ring->ntu) + len - READ_ONCE(ring->ntc)) % len;
 }
 
 netdev_tx_t hbg_net_start_xmit(struct sk_buff *skb, struct net_device *netdev);
-- 
2.33.0