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

Marcel Holtmann
2021-12-16T19:58:35Z

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
>>>
>>> So Marcel, do I read it right that you are working on a fix
>>> and I can drop this patch for now?
>>
>> ping
>
>
> If I don't hear otherwise I'll queue my version - it might not
> be ideal but it at least does not violate the spec.
> We can work on not allocating/freeing buffers later
> as appropriate.

I have a patch, but it is not fully tested yet.

Regards

Marcel