netdev - Re: [PATCH] net: Add etun driver

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Date:	Fri, 06 Apr 2007 13:57:25 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	Jeff Garzik <jgarzik@...ox.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Ben Greear <greearb@...delatech.com>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Dmitry Mishin <dim@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>
Subject: Re: [PATCH] net: Add etun driver

 > +/*
 > + * The higher levels take care of making this non-reentrant (it's
 > + * called with bh's disabled).
 > + */
 > +static int etun_xmit(struct sk_buff *skb, struct net_device *tx_dev)

You have this comment, but then...

 > +	dev->features		= NETIF_F_FRAGLIST
 > +				  | NETIF_F_HIGHDMA
 > +				  | NETIF_F_LLTX;

you set LLTX, which means that the upper layers _don't_ make sure that
your xmit routine is not reentrant.

It looks like the impact of multiple simultaneous xmit calls is just
the possibility of screwing up the statistics, but still I think you
want to drop the LLTX feature (since you have no lock of your own to
try and take).
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