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

Marcel Holtmann
2021-11-25T20:04:06Z

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