netdev - Aw: [PATCH v2] ethernet:arc: Fix racing of TX ring buffer

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Date:	Tue, 17 May 2016 18:36:11 +0200
From:	"Lino Sanfilippo" <LinoSanfilippo@....de>
To:	"Shuyu Wei" <wsy2220@...il.com>
Cc:	wxt@...k-chips.com, davem@...emloft.net, romieu@...zoreil.com,
	heiko@...ech.de, linux-rockchip@...ts.infradead.org,
	netdev@...r.kernel.org
Subject: Aw: [PATCH v2] ethernet:arc: Fix racing of TX ring buffer

Hi,

> Von: "Shuyu Wei" <wsy2220@...il.com>
> @@ -685,13 +684,15 @@ static int arc_emac_tx(struct sk_buff *skb, struct net_device *ndev)
>  	wmb();
>  
>  	skb_tx_timestamp(skb);
> +	priv->tx_buff[*txbd_curr].skb = skb;
> +
> +	dma_wmb();
>  
>  	*info = cpu_to_le32(FOR_EMAC | FIRST_OR_LAST_MASK | len);
>  
>  	/* Make sure info word is set */
>  	wmb();
>  
> -	priv->tx_buff[*txbd_curr].skb = skb;
>  
>  	/* Increment index to point to the next BD */
>  	*txbd_curr = (*txbd_curr + 1) % TX_BD_NUM;
> 

I wonder if this is correct. AFAIK a dma_wmb() only guarantees ordering of writes to DMA memory.
The assignment of the skb however is to RAM not to DMA.


Regards,
Lino