netdev - Re: Deadlock, L2TP over IP are not working, 3.4.1

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Message-ID: <1339104606.6001.4.camel@edumazet-glaptop>
Date:	Thu, 07 Jun 2012 23:30:06 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Francois Romieu <romieu@...zoreil.com>
Cc:	Denys Fedoryshchenko <denys@...p.net.lb>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Deadlock, L2TP over IP are not working, 3.4.1

On Thu, 2012-06-07 at 22:53 +0200, Francois Romieu wrote:

> Any reason why it could not be made LLTX ?
> 

>  /* via l2tp_session_priv() */
> @@ -87,25 +95,56 @@ static int l2tp_eth_dev_xmit(struct sk_buff *skb, struct net_device *dev)
>  {
>  	struct l2tp_eth *priv = netdev_priv(dev);
>  	struct l2tp_session *session = priv->session;
> +	struct l2tp_eth_stats *tstats = &priv->tstats;
>  
>  	l2tp_xmit_skb(session, skb, session->hdr_len);
>  
> -	dev->stats.tx_bytes += skb->len;
> -	dev->stats.tx_packets++;
> +	u64_stats_update_begin(&tstats->syncp);
> +	tstats->packets++;
> +	tstats->bytes += skb->len;
> +	u64_stats_update_end(&tstats->syncp);
>  
>  	return 0;
>  }
>  

Its racy.

If LLTX is used, this means several cpus can execute this code at the
same time.

You need percpu stats, or use atomic primitives.



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