diff mbox

[V2,6/8] net: mediatek: fix TX locking

Message ID 1460057210-55786-7-git-send-email-blogic@openwrt.org
State Changes Requested, archived
Delegated to: David Miller
Headers show

Commit Message

John Crispin April 7, 2016, 7:26 p.m. UTC 
Inside the TX path there is a lock inside the tx_map function. This is
however too late. The patch moves the lock to the start of the xmit
function right before the free count check of the DMA ring happens.
If we do not do this, the code becomes racy leading to TX stalls and
dropped packets. This happens as there are 2 netdevs running on the
same physical DMA ring.

Signed-off-by: John Crispin <blogic@openwrt.org>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

Comments

Sergei Shtylyov April 7, 2016, 7:46 p.m. UTC | #1 
Hello.

On 04/07/2016 10:26 PM, John Crispin wrote:

> Inside the TX path there is a lock inside the tx_map function. This is
> however too late. The patch moves the lock to the start of the xmit
> function right before the free count check of the DMA ring happens.
> If we do not do this, the code becomes racy leading to TX stalls and
> dropped packets. This happens as there are 2 netdevs running on the
> same physical DMA ring.
>
> Signed-off-by: John Crispin <blogic@openwrt.org>
> ---
>   drivers/net/ethernet/mediatek/mtk_eth_soc.c |   20 ++++++++++----------
>   1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index 60b66ab..8434355 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
[...]
> @@ -712,14 +702,22 @@ static int mtk_start_xmit(struct sk_buff *skb, struct net_device *dev)
>   	struct mtk_eth *eth = mac->hw;
>   	struct mtk_tx_ring *ring = &eth->tx_ring;
>   	struct net_device_stats *stats = &dev->stats;
> +	unsigned long flags;
>   	bool gso = false;
>   	int tx_num;
>
> +	/* normally we can rely on the stack not calling this more than once,
> +	 * however we have 2 queues running ont he same ring so we need to lock

    s/ont he/ on the/, perhaps a good chance to fix the comment?

> +	 * the ring access
> +	 */
> +	spin_lock_irqsave(&eth->page_lock, flags);
> +
>   	tx_num = mtk_cal_txd_req(skb);
>   	if (unlikely(atomic_read(&ring->free_count) <= tx_num)) {
>   		mtk_stop_queue(eth);
>   		netif_err(eth, tx_queued, dev,
>   			  "Tx Ring full when queue awake!\n");
> +		spin_unlock_irqrestore(&eth->page_lock, flags);
>   		return NETDEV_TX_BUSY;
>   	}
>
[...]

MBR, Sergei
diff mbox

Patch

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 60b66ab..8434355 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -536,7 +536,6 @@  static int mtk_tx_map(struct sk_buff *skb, struct net_device *dev,
 	struct mtk_eth *eth = mac->hw;
 	struct mtk_tx_dma *itxd, *txd;
 	struct mtk_tx_buf *tx_buf;
-	unsigned long flags;
 	dma_addr_t mapped_addr;
 	unsigned int nr_frags;
 	int i, n_desc = 1;
@@ -568,11 +567,6 @@  static int mtk_tx_map(struct sk_buff *skb, struct net_device *dev,
 	if (unlikely(dma_mapping_error(&dev->dev, mapped_addr)))
 		return -ENOMEM;
 
-	/* normally we can rely on the stack not calling this more than once,
-	 * however we have 2 queues running ont he same ring so we need to lock
-	 * the ring access
-	 */
-	spin_lock_irqsave(&eth->page_lock, flags);
 	WRITE_ONCE(itxd->txd1, mapped_addr);
 	tx_buf->flags |= MTK_TX_FLAGS_SINGLE0;
 	dma_unmap_addr_set(tx_buf, dma_addr0, mapped_addr);
@@ -632,8 +626,6 @@  static int mtk_tx_map(struct sk_buff *skb, struct net_device *dev,
 	WRITE_ONCE(itxd->txd3, (TX_DMA_SWC | TX_DMA_PLEN0(skb_headlen(skb)) |
 				(!nr_frags * TX_DMA_LS0)));
 
-	spin_unlock_irqrestore(&eth->page_lock, flags);
-
 	netdev_sent_queue(dev, skb->len);
 	skb_tx_timestamp(skb);
 
@@ -661,8 +653,6 @@  err_dma:
 		itxd = mtk_qdma_phys_to_virt(ring, itxd->txd2);
 	} while (itxd != txd);
 
-	spin_unlock_irqrestore(&eth->page_lock, flags);
-
 	return -ENOMEM;
 }
 
@@ -712,14 +702,22 @@  static int mtk_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct mtk_eth *eth = mac->hw;
 	struct mtk_tx_ring *ring = &eth->tx_ring;
 	struct net_device_stats *stats = &dev->stats;
+	unsigned long flags;
 	bool gso = false;
 	int tx_num;
 
+	/* normally we can rely on the stack not calling this more than once,
+	 * however we have 2 queues running ont he same ring so we need to lock
+	 * the ring access
+	 */
+	spin_lock_irqsave(&eth->page_lock, flags);
+
 	tx_num = mtk_cal_txd_req(skb);
 	if (unlikely(atomic_read(&ring->free_count) <= tx_num)) {
 		mtk_stop_queue(eth);
 		netif_err(eth, tx_queued, dev,
 			  "Tx Ring full when queue awake!\n");
+		spin_unlock_irqrestore(&eth->page_lock, flags);
 		return NETDEV_TX_BUSY;
 	}
 
@@ -747,10 +745,12 @@  static int mtk_start_xmit(struct sk_buff *skb, struct net_device *dev)
 			     ring->thresh))
 			mtk_wake_queue(eth);
 	}
+	spin_unlock_irqrestore(&eth->page_lock, flags);
 
 	return NETDEV_TX_OK;
 
 drop:
+	spin_unlock_irqrestore(&eth->page_lock, flags);
 	stats->tx_dropped++;
 	dev_kfree_skb(skb);
 	return NETDEV_TX_OK;