Re: [PATCH] Bluetooth: virtio_bt: fix device removal

Michael S. Tsirkin
2021-11-25T20:47:04Z

On Thu, Nov 25, 2021 at 09:02:01PM +0100, Marcel Holtmann wrote:
> Hi Michael,
>
> > Device removal is clearly out of virtio spec: it attempts to remove
> > unused buffers from a VQ before invoking device reset. To fix, make
> > open/close NOPs and do all cleanup/setup in probe/remove.
>
> so the virtbt_{open,close} as NOP is not really what a driver is suppose
> to be doing. These are transport enable/disable callbacks from the BT
> Core towards the driver. It maps to a device being enabled/disabled by
> something like bluetoothd for example. So if disabled, I expect that no
> resources/queues are in use.
>
> Maybe I misunderstand the virtio spec in that regard, but I would like
> to keep this fundamental concept of a Bluetooth driver. It does work
> with all other transports like USB, SDIO, UART etc.
>
> > The cost here is a single skb wasted on an unused bt device - which
> > seems modest.
>
> There should be no buffer used if the device is powered off. We also don’t
> have any USB URBs in-flight if the transport is not active.
>
> > NB: with this fix in place driver still suffers from a race condition if
> > an interrupt triggers while device is being reset. Work on a fix for
> > that issue is in progress.
>
> In the virtbt_close() callback we should deactivate all interrupts.
>
> Regards
>
> Marcel

If you want to do that then device has to be reset on close,
and fully reinitialized on open.
Can you work on a patch like that?
Given I don't have the device such a rework is probably more
than I can undertake.

--
MST