[PATCH net v2] net: nixge: stop IRQ producers before draining DMA error tasklet

[PATCH net v2] net: nixge: stop IRQ producers before draining DMA error tasklet

[Myeonghun Pak]

The TX and RX IRQ handlers can reschedule dma_err_tasklet after
tasklet_kill(), allowing it to access rings freed by nixge_stop().

Free both IRQs before killing the tasklet. Since pending recovery can
restart DMA, mask channel interrupts and wait for a DMA reset to finish
before releasing the rings. Clearing RUNSTOP alone does not ensure that
outstanding DMA accesses have completed.

If reset times out, retain the DMA buffers and reject subsequent opens
to prevent those buffers from being freed or their pointers overwritten.

Fixes: 492caffa8a1a ("net: ethernet: nixge: Add support for National Instruments XGE netdev")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Co-developed-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Myeonghun Pak <mhun512@gmail.com>
---
Changes in v2:
- Wait for DMA reset completion; retain buffers and reject reopen on timeout.

Based on net commit 6dc989ea46b96ce170840174b4a38c4a387fb005.
No hardware testing was performed.

 drivers/net/ethernet/ni/nixge.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/ni/nixge.c b/drivers/net/ethernet/ni/nixge.c
index 230d5ff..878ca67 100644
--- a/drivers/net/ethernet/ni/nixge.c
+++ b/drivers/net/ethernet/ni/nixge.c
@@ -185,6 +185,7 @@ struct nixge_priv {
 	void __iomem *dma_regs;
 
 	struct tasklet_struct dma_err_tasklet;
+	bool dma_stop_failed;
 
 	int tx_irq;
 	int rx_irq;
@@ -391,7 +392,7 @@ out:
 	return -ENOMEM;
 }
 
-static void __nixge_device_reset(struct nixge_priv *priv, off_t offset)
+static int __nixge_device_reset(struct nixge_priv *priv, off_t offset)
 {
 	u32 status;
 	int err;
@@ -407,6 +408,8 @@ static void __nixge_device_reset(struct nixge_priv *priv, off_t offset)
 				     1000);
 	if (err)
 		netdev_err(priv->ndev, "%s: DMA reset timeout!\n", __func__);
+
+	return err;
 }
 
 static void nixge_device_reset(struct net_device *ndev)
@@ -869,6 +872,10 @@ static int nixge_open(struct net_device *ndev)
 	struct phy_device *phy;
 	int ret;
 
+	/* A failed stop retained buffers which DMA may still be using. */
+	if (priv->dma_stop_failed)
+		return -EIO;
+
 	nixge_device_reset(ndev);
 
 	phy = of_phy_connect(ndev, priv->phy_node,
@@ -911,6 +918,7 @@ static int nixge_stop(struct net_device *ndev)
 {
 	struct nixge_priv *priv = netdev_priv(ndev);
 	u32 cr;
+	int ret;
 
 	netif_stop_queue(ndev);
 	napi_disable(&priv->napi);
@@ -920,6 +928,7 @@ static int nixge_stop(struct net_device *ndev)
 		phy_disconnect(ndev->phydev);
 	}
 
+	/* Stop DMA while the completion IRQ handlers are still installed. */
 	cr = nixge_dma_read_reg(priv, XAXIDMA_RX_CR_OFFSET);
 	nixge_dma_write_reg(priv, XAXIDMA_RX_CR_OFFSET,
 			    cr & (~XAXIDMA_CR_RUNSTOP_MASK));
@@ -927,11 +936,29 @@ static int nixge_stop(struct net_device *ndev)
 	nixge_dma_write_reg(priv, XAXIDMA_TX_CR_OFFSET,
 			    cr & (~XAXIDMA_CR_RUNSTOP_MASK));
 
-	tasklet_kill(&priv->dma_err_tasklet);
-
+	/* Remove both producers before draining the error tasklet. */
 	free_irq(priv->tx_irq, ndev);
 	free_irq(priv->rx_irq, ndev);
 
+	tasklet_kill(&priv->dma_err_tasklet);
+
+	/* Error recovery may have restarted DMA and enabled interrupts. */
+	cr = nixge_dma_read_reg(priv, XAXIDMA_RX_CR_OFFSET);
+	nixge_dma_write_reg(priv, XAXIDMA_RX_CR_OFFSET,
+			    cr & ~(XAXIDMA_CR_RUNSTOP_MASK | XAXIDMA_IRQ_ALL_MASK));
+	cr = nixge_dma_read_reg(priv, XAXIDMA_TX_CR_OFFSET);
+	nixge_dma_write_reg(priv, XAXIDMA_TX_CR_OFFSET,
+			    cr & ~(XAXIDMA_CR_RUNSTOP_MASK | XAXIDMA_IRQ_ALL_MASK));
+
+	/* Either channel's reset quiesces the entire AXI DMA engine. */
+	ret = __nixge_device_reset(priv, XAXIDMA_TX_CR_OFFSET);
+	if (ret) {
+		/* Retain DMA buffers and prevent a subsequent open replacing them. */
+		priv->dma_stop_failed = true;
+		netdev_err(ndev, "DMA stop failed; retaining DMA buffers\n");
+		return ret;
+	}
+
 	nixge_hw_dma_bd_release(ndev);
 
 	return 0;
-- 
2.53.0