Re: [PATCH net-next] net: stmmac: add BQL support

From: Florian Fainelli
Date: Mon Dec 29 2014 - 02:49:14 EST

2014-12-28 6:57 GMT-08:00 Beniamino Galvani <b.galvani@xxxxxxxxx>:
> Add support for Byte Queue Limits to the STMicro MAC driver.
> Tested on a Amlogic S805 Cortex-A5 board, where the use of BQL
> slightly decreases the ping latency from ~10ms to ~3ms when the
> 100Mbps link is saturated by TCP streams. No difference is
> observed at 1Gbps.
> Signed-off-by: Beniamino Galvani <b.galvani@xxxxxxxxx>
> ---


> priv->dev->stats.tx_errors++;
> @@ -2049,6 +2057,7 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
> skb_tx_timestamp(skb);
> priv->hw->dma->enable_dma_transmission(priv->ioaddr);
> + netdev_sent_queue(dev, skb->len);

You are introducing a potential use after free here in case tx_lock is
eliminated one day and your TX reclaim logic kicks in and frees the
freshly transmitted SKB, it would be safer to just cache skb->len in a
local variable, and use it here.

> spin_unlock(&priv->tx_lock);
> return NETDEV_TX_OK;
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