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

Hi Michael,

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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.

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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.

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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.

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.

so you mean move virtio_find_vqs() into virtbt_open() and del_vqs() into
virtbt_close()?

Or is there are way to set up the queues without starting them?

However I am failing to understand your initial concern, we do reset()
before del_vqs() in virtbt_remove(). Should we be doing something different
in virtbt_close() other than virtqueue_detach_unused_buf(). Why would I
keep buffers attached if they are not used.

Regards

Marcel