linux-kernel - Re: [PATCH] virtio: Don't access index after unregister.

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Message-ID: <877gpv2yjx.fsf@rustcorp.com.au>
Date:	Fri, 09 Nov 2012 14:54:50 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Cornelia Huck <cornelia.huck@...ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio: Don't access index after unregister.

Cornelia Huck <cornelia.huck@...ibm.com> writes:
> Virtio wants to release used indices after the corresponding
> virtio device has been unregistered. However, virtio does not
> hold an extra reference, giving up its last reference with
> device_unregister(), making accessing dev->index afterwards
> invalid.
>
> I actually saw problems when testing my (not-yet-merged)
> virtio-ccw code:
>
> - device_add virtio-net,id=xxx
> -> creates device virtio<n> with n>0
>
> - device_del xxx
> -> deletes virtio<n>, but calls ida_simple_remove with an
>    index of 0
>
> - device_add virtio-net,id=xxx
> -> tries to add virtio0, which is still in use...
>
> So let's save the index we want to release before calling
> device_unregister().

Great catch!  I've add a CC:stable.

Applied,
Rusty.
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