From mboxrd@z Thu Jan  1 00:00:00 1970
From: Francois Romieu <romieu@fr.zoreil.com>
Subject: Re: [PATCH v2] ethernet:arc: Fix racing of TX ring buffer
Date: Sat, 21 May 2016 21:47:33 +0200
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Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>,
	David Miller <davem@davemloft.net>, wxt@rock-chips.com,
	heiko@sntech.de, linux-rockchip@lists.infradead.org,
	netdev@vger.kernel.org
To: Shuyu Wei <wsy2220@gmail.com>
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Shuyu Wei <wsy2220@gmail.com> :
[...]
> diff --git a/drivers/net/ethernet/arc/emac_main.c b/drivers/net/ethernet/arc/emac_main.c
> index a3a9392..c2447b0 100644
> --- a/drivers/net/ethernet/arc/emac_main.c
> +++ b/drivers/net/ethernet/arc/emac_main.c
> @@ -686,6 +686,9 @@ static int arc_emac_tx(struct sk_buff *skb, struct net_device *ndev)
>  
>         skb_tx_timestamp(skb);
>  
> +       /* Make sure timestamp is set */
> +       smp_wmb();

Should be dma_wmb() (see davem's message).

It's completely unrelated to SMP.

-- 
Ueimor