On Thu, Nov 08, 2012 at 11:43:47AM +0100, Cornelia Huck wrote:
> 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().
>
> Signed-off-by: Cornelia Huck <[email protected]>
> ---
> drivers/virtio/virtio.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 1e8659c..809b0de 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -225,8 +225,10 @@ EXPORT_SYMBOL_GPL(register_virtio_device);
>
> void unregister_virtio_device(struct virtio_device *dev)
> {
> + int index = dev->index; /* save for after device release */
It's obvious from code that we safe for after release,
I think a better comment would explain *why* we do this.
Something like
/*
device_unregister drops reference to device so put_device could
invoke release callback. In case that callback will free the device,
make sure we don't access device after this call.
*/
int index = dev->index;
?
> +
> device_unregister(&dev->dev);
> - ida_simple_remove(&virtio_index_ida, dev->index);
> + ida_simple_remove(&virtio_index_ida, index);
> }
> EXPORT_SYMBOL_GPL(unregister_virtio_device);
>
> --
> 1.7.12.4
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