netdev - Re: tun: Use netif_receive_skb instead of netif

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Message-ID: <20100521105128.GA29521@hmsreliant.think-freely.org>
Date:	Fri, 21 May 2010 06:51:28 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	David Miller <davem@...emloft.net>
Cc:	herbert@...dor.apana.org.au, eric.dumazet@...il.com,
	bmb@...enacr.com, tgraf@...hat.com, nhorman@...hat.com,
	netdev@...r.kernel.org
Subject: Re: tun: Use netif_receive_skb instead of netif_rx

On Thu, May 20, 2010 at 10:49:44PM -0700, David Miller wrote:
> From: Neil Horman <nhorman@...driver.com>
> Date: Thu, 20 May 2010 20:39:39 -0400
> 
> > On Fri, May 21, 2010 at 09:16:30AM +1000, Herbert Xu wrote:
> >> On Thu, May 20, 2010 at 01:29:18PM -0400, Neil Horman wrote:
> >> >
> >> > So, I'm testing this patch out now, and unfotunately it doesn't seem to be
> >> > working.  Every frame seems to be holding a classid of 0.  Trying to figure out
> >> > why now.
> >> 
> >> Not very surprising since tun.c doesn't go through the normal
> >> socket interface.  I'll send a additional patch for that.
> >> 
> > I don't think thats it.  I think its a chicken and egg situation.  I think the
> > problem is that tasks can't be assigned to cgroups until their created, and in
> > that time a sock can be created.  Its a natural race.  If you create a socket
> > before you assign it to a cgroup, that socket retains a classid of zero.  I'm
> > going to try modify the patch to update sockets owned by tasks when the cgroup
> > is assigned.
> 
> Neil, you must not be using Herbert's most recent patch.
> 
I'm not, I was testing the version prior. I wrote my note before he posted the
update for the tun driver

> Either that or you haven't even read it.
> 
I read it, we just described the issue in diferent terms.

Neil

> Herbert's most recent patch doesn't create this chicken and egg
> problem you mention because it explicitly watches for cgroupid changes
> at all socket I/O operations including sendmsg() and sendmsg().  And
> if it sees a different cgroupid at a socket I/O call, it updates the
> cgroupid value in the socket.
> 
> So you very much can change the cgroup of the process mid-socket
> ownership and it will work.
> 
> The only problem is, as Herbert stated, tun.  Because it does it's
> networking I/O directly by calling netif_receive_skb() so it won't
> hit any of Herbert's cgroup check points.
> 
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