linux-kernel - Re: [PATCH v3] Bluetooth: virtio

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Date:   Mon, 15 Aug 2022 16:23:37 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Hulk Robot <hulkci@...wei.com>,
        Yang Yingliang <yangyingliang@...wei.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>
Subject: Re: [PATCH v3] Bluetooth: virtio_bt: fix device removal

On Mon, Aug 15, 2022 at 11:07:05AM -0700, Luiz Augusto von Dentz wrote:
> Hi Michael,
> 
> On Thu, Aug 11, 2022 at 2:46 AM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > 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.
> >
> > NB: This is a hacky way to handle this - virtbt_{open,close} as NOP is
> > not really what a driver is supposed 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, users expect that no resources/queues are in
> > use.  It does work with all other transports like USB, SDIO, UART etc.
> > 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.
> >
> > The way to implement a proper fix would be using vq reset if supported,
> > or even using a full device reset.
> >
> > The cost of the hack is a single skb wasted on an unused bt device.
> >
> > NB2: with this fix in place driver still suffers from a race condition
> > if an interrupt triggers while device is being reset.  To fix, in the
> > virtbt_close() callback we should deactivate all interrupts.  To be
> > fixed.
> >
> > squashed fixup: bluetooth: virtio_bt: fix an error code in probe()
> 
> Shouldn't the line above be a Fixes tag with the commit hash you are
> attempting to fix, other than that I'd be fine to apply these changes.

No - what I tried to say here is that I posted the original patch
and then Dan and Yang posted fixups, I squashed them in but
wanted to keep contribution.


> > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > Reported-by: Hulk Robot <hulkci@...wei.com>
> > Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > Message-Id: <20220811080943.198245-1-mst@...hat.com>
> > ---
> >
> > changes from v2:
> >         tkeaked commit log to make lines shorter
> > changes from v1:
> >         fixed error handling
> >
> >  drivers/bluetooth/virtio_bt.c | 19 +++++++++++++++++--
> >  1 file changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/bluetooth/virtio_bt.c b/drivers/bluetooth/virtio_bt.c
> > index 67c21263f9e0..f6d699fed139 100644
> > --- a/drivers/bluetooth/virtio_bt.c
> > +++ b/drivers/bluetooth/virtio_bt.c
> > @@ -50,8 +50,11 @@ static int virtbt_add_inbuf(struct virtio_bluetooth *vbt)
> >
> >  static int virtbt_open(struct hci_dev *hdev)
> >  {
> > -       struct virtio_bluetooth *vbt = hci_get_drvdata(hdev);
> > +       return 0;
> > +}
> >
> > +static int virtbt_open_vdev(struct virtio_bluetooth *vbt)
> > +{
> >         if (virtbt_add_inbuf(vbt) < 0)
> >                 return -EIO;
> >
> > @@ -61,7 +64,11 @@ static int virtbt_open(struct hci_dev *hdev)
> >
> >  static int virtbt_close(struct hci_dev *hdev)
> >  {
> > -       struct virtio_bluetooth *vbt = hci_get_drvdata(hdev);
> > +       return 0;
> > +}
> > +
> > +static int virtbt_close_vdev(struct virtio_bluetooth *vbt)
> > +{
> >         int i;
> >
> >         cancel_work_sync(&vbt->rx);
> > @@ -354,8 +361,15 @@ static int virtbt_probe(struct virtio_device *vdev)
> >                 goto failed;
> >         }
> >
> > +       virtio_device_ready(vdev);
> > +       err = virtbt_open_vdev(vbt);
> > +       if (err)
> > +               goto open_failed;
> > +
> >         return 0;
> >
> > +open_failed:
> > +       hci_free_dev(hdev);
> >  failed:
> >         vdev->config->del_vqs(vdev);
> >         return err;
> > @@ -368,6 +382,7 @@ static void virtbt_remove(struct virtio_device *vdev)
> >
> >         hci_unregister_dev(hdev);
> >         virtio_reset_device(vdev);
> > +       virtbt_close_vdev(vbt);
> >
> >         hci_free_dev(hdev);
> >         vbt->hdev = NULL;
> > --
> > MST
> >
> 
> 
> -- 
> Luiz Augusto von Dentz