[PATCH net-next v3] net: dlink: add synchronization for stats update

[Moon Yeounsu <yyyynoom@gmail.com>]

This patch synchronizes code that accesses from both user-space
and IRQ contexts. The `get_stats()` function can be called from both
context.

`dev->stats.tx_errors` and `dev->stats.collisions` are also updated
in the `tx_errors()` function. Therefore, these fields must also be
protected by synchronized.

There is no code that accessses `dev->stats.tx_errors` between the
previous and updated lines, so the updating point can be moved.

Signed-off-by: Moon Yeounsu <yyyynoom@gmail.com>
---
Changelog:
v1: https://lore.kernel.org/netdev/20250421191645.43526-2-yyyynoom@gmail.com/
v2: https://lore.kernel.org/netdev/20250425231352.102535-2-yyyynoom@gmail.com/
- fix incorrect method of updating `dev->stats.tx_errors` and
  `dev->stats.collisions`
v3:
- fix incorrect locking method
---
 drivers/net/ethernet/dlink/dl2k.c | 14 +++++++++++++-
 drivers/net/ethernet/dlink/dl2k.h |  2 ++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/dlink/dl2k.c b/drivers/net/ethernet/dlink/dl2k.c
index 232e839a9d07..038a0400c1f9 100644
--- a/drivers/net/ethernet/dlink/dl2k.c
+++ b/drivers/net/ethernet/dlink/dl2k.c
@@ -146,6 +146,8 @@ rio_probe1 (struct pci_dev *pdev, const struct pci_device_id *ent)
 	np->ioaddr = ioaddr;
 	np->chip_id = chip_idx;
 	np->pdev = pdev;
+
+	spin_lock_init(&np->stats_lock);
 	spin_lock_init (&np->tx_lock);
 	spin_lock_init (&np->rx_lock);
 
@@ -865,7 +867,6 @@ tx_error (struct net_device *dev, int tx_status)
 	frame_id = (tx_status & 0xffff0000);
 	printk (KERN_ERR "%s: Transmit error, TxStatus %4.4x, FrameId %d.\n",
 		dev->name, tx_status, frame_id);
-	dev->stats.tx_errors++;
 	/* Ttransmit Underrun */
 	if (tx_status & 0x10) {
 		dev->stats.tx_fifo_errors++;
@@ -902,9 +903,15 @@ tx_error (struct net_device *dev, int tx_status)
 		rio_set_led_mode(dev);
 		/* Let TxStartThresh stay default value */
 	}
+
+	spin_lock(&np->stats_lock);
 	/* Maximum Collisions */
 	if (tx_status & 0x08)
 		dev->stats.collisions++;
+
+	dev->stats.tx_errors++;
+	spin_unlock(&np->stats_lock);
+
 	/* Restart the Tx */
 	dw32(MACCtrl, dr16(MACCtrl) | TxEnable);
 }
@@ -1073,7 +1080,9 @@ get_stats (struct net_device *dev)
 	int i;
 #endif
 	unsigned int stat_reg;
+	unsigned long flags;
 
+	spin_lock_irqsave(&np->stats_lock, flags);
 	/* All statistics registers need to be acknowledged,
 	   else statistic overflow could cause problems */
 
@@ -1123,6 +1132,9 @@ get_stats (struct net_device *dev)
 	dr16(TCPCheckSumErrors);
 	dr16(UDPCheckSumErrors);
 	dr16(IPCheckSumErrors);
+
+	spin_unlock_irqrestore(&np->stats_lock, flags);
+
 	return &dev->stats;
 }
 
diff --git a/drivers/net/ethernet/dlink/dl2k.h b/drivers/net/ethernet/dlink/dl2k.h
index 0e33e2eaae96..56aff2f0bdbf 100644
--- a/drivers/net/ethernet/dlink/dl2k.h
+++ b/drivers/net/ethernet/dlink/dl2k.h
@@ -372,6 +372,8 @@ struct netdev_private {
 	struct pci_dev *pdev;
 	void __iomem *ioaddr;
 	void __iomem *eeprom_addr;
+	// To ensure synchronization when stats are updated.
+	spinlock_t stats_lock;
 	spinlock_t tx_lock;
 	spinlock_t rx_lock;
 	unsigned int rx_buf_sz;		/* Based on MTU+slack. */
-- 
2.49.0