netdev - Re: [PATCH 0/3 v4] macvtap driver

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Message-Id: <1265825143.30414.81.camel@w-sridhar.beaverton.ibm.com>
Date:	Wed, 10 Feb 2010 10:05:43 -0800
From:	Sridhar Samudrala <sri@...ibm.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Ed Swierk <eswierk@...stanetworks.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 0/3 v4] macvtap driver

On Wed, 2010-02-10 at 15:48 +0100, Arnd Bergmann wrote:
> On Monday 08 February 2010, Sridhar Samudrala wrote:
> > I am also seeing this issue with net-next-2.6.
> > Basically macvtap_put_user() and macvtap_get_user() call copy_to/from_user
> > from within a RCU read-side critical section.
> > 
> > The following patch fixes this issue by releasing the RCU read lock before
> > calling these routines, but instead hold a reference to q->sk.
> > 
> > Signed-off-by: Sridhar Samudrala <sri@...ibm.com>
> 
> Yes, we need something like this, but we also need to protect the
> device from going away. The concept right now is to use file_get_queue
> to protect both the macvtap_queue and the macvlan_dev from going
> away. The sock_hold will keep the macvtap_queue around, but
> as far as I can tell, a user could still destroy the macvlan_dev
> using netlink at the same time, which still breaks.

may be we should do a dev_hold() in macvtap_set_queue() and dev_put()
in macvtap_del_queue() so that the underlying device cannot go away as
long the macvtap fd is open.

Thanks
Sridhar

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