Date:   Thu, 9 Dec 2021 16:22:52 -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
Message-ID: <20211209162149-mutt-send-email-mst@kernel.org>
References: <20211125174200.133230-1-mst@redhat.com>
 <F52F65FE-6A07-486B-8E84-684ED85709E9@holtmann.org>
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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

So Marcel, do I read it right that you are working on a fix
and I can drop this patch for now?

-- 
MST