netdev - Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server

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Message-ID: <20091104130828.GC8920@redhat.com>
Date:	Wed, 4 Nov 2009 15:08:28 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, mingo@...e.hu,
	linux-mm@...ck.org, akpm@...ux-foundation.org
Subject: Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server

On Wed, Nov 04, 2009 at 01:59:57PM +0100, Andi Kleen wrote:
> > Fine?
> 
> I cannot say -- are there paths that could drop the device beforehand?

Do you mean drop the mm reference?

> (as in do you hold a reference to it?)

By design I think I always have a reference to mm before I use it.

This works like this:
ioctl SET_OWNER - calls get_task_mm, I think this gets a reference to mm
ioctl SET_BACKEND - checks that SET_OWNER was run, starts virtqueue
ioctl RESET_OWNER - stops virtqueues, drops the reference to mm
file close - stops virtqueues, if we still have it then drops mm

This is why I think I can call use_mm/unuse_mm while virtqueue is running,
safely.
Makes sense?

> -Andi
> -- 
> ak@...ux.intel.com -- Speaking for myself only.
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