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Date:   Fri, 14 Jan 2022 15:12:42 -0500
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Marcel Holtmann <marcel@holtmann.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        linux-bluetooth@vger.kernel.org,
        virtualization@lists.linux-foundation.org
Subject: Re: [PATCH] Bluetooth: virtio_bt: fix device removal
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On Thu, Dec 16, 2021 at 08:58:31PM +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
> >>> 
> >>> 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

ping

it's been a month ...

I'm working on cleaning up module/device removal in virtio and bt
is kind of sticking out.

-- 
MST