Messages in this thread | | | Date | Tue, 12 Apr 2011 10:09:12 +0100 | Subject | Re: [PATCH] virtio: decrement dev_index when device is unregistered | From | Stefan Hajnoczi <> |
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On Mon, Apr 11, 2011 at 10:11 AM, Takuma Umeya <tumeya@redhat.com> wrote: > ----- Original Message ----- >> On Tue, Apr 5, 2011 at 5:49 AM, Takuma Umeya <tumeya@redhat.com> >> wrote: >> > When virtio device is removed, dev_index does not get decremented. >> > The next device hotplug event results in consuming the next pci to >> > the one that is suppose to be available. >> > >> > Signed-off-by: Takuma Umeya <tumeya@redhat.com> >> > >> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c >> > index efb35aa..67fe71d 100644 >> > --- a/drivers/virtio/virtio.c >> > +++ b/drivers/virtio/virtio.c >> > @@ -216,6 +216,7 @@ EXPORT_SYMBOL_GPL(register_virtio_device); >> > void unregister_virtio_device(struct virtio_device *dev) >> > { >> > device_unregister(&dev->dev); >> > + dev_index--; >> >> I don't think there is any guarantee that virtio devices are >> added/removed in first-in-last-out order. >> >> That means I could add a virtio-net device (index 0) followed by a >> virtio-blk device (index 1). Now I remove the virtio-net device >> (index 0) which causes me to decrement dev_index and hand index 1 out >> again to the next device. This leaves us with virtio-blk (index 1) >> and the new device with index 1, which is not unique. >> >> Perhaps I missed a constraint which prevents this from occurring? > I believe the address is assigned up to 1f so using u32 value > to track use/free. This should make the code immune to the scenario. > Would this be adequate?
This issue was also brought up by Jens Axboe on your other patch for virtio block devices. He suggested using idr. I think that would be a nicer solution than a u32 bitfield.
I'm not sure where you got 0x1f from but that seems like an artifical limitation. Nothing should stop us from having more virtio devices.
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