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From:   Jesse Melhuish <melhuishj@chromium.org>
Date:   Fri, 12 Nov 2021 17:03:10 -0600
Message-ID: <CACGnfjSdxUGj=6Wk-oUcH-jwe3PYMm9gbPdi_atmaozN8A-mWg@mail.gmail.com>
Subject: Re: [PATCH v2] Bluetooth: Don't initialize msft/aosp when using user channel
To:     Jesse Melhuish <melhuishj@chromium.org>
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        linux-bluetooth <linux-bluetooth@vger.kernel.org>,
        Abhishek Pandit-Subedi <abhishekpandit@chromium.org>,
        Sonny Sasaka <sonnysasaka@chromium.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
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Hi Marcel,

Forgot to include: patch v3 incorporating your feedback will follow
very shortly.

On Fri, Nov 12, 2021 at 4:50 PM Jesse Melhuish <melhuishj@chromium.org> wrote:
>
> Hi Marcel,
>
> No problem, thanks. Happy to extend userchan-tester; do you mind if we
> continue reviewing this patch for approval in the meantime so we can
> mitigate the issue on our end?
>
> On Thu, Nov 11, 2021 at 12:43 PM Marcel Holtmann <marcel@holtmann.org> wrote:
> >
> > Hi Jesse,
> >
> > > A race condition is triggered when usermode control is given to
> > > userspace before the kernel's MSFT query responds, resulting in an
> > > unexpected response to userspace's reset command.
> > >
> > > Issue can be observed in btmon:
> > > < HCI Command: Vendor (0x3f|0x001e) plen 2                    #3 [hci0]
> > >        05 01                                            ..
> > > @ USER Open: bt_stack_manage (privileged) version 2.22  {0x0002} [hci0]
> > > < HCI Command: Reset (0x03|0x0003) plen 0                     #4 [hci0]
> > >> HCI Event: Command Complete (0x0e) plen 5                   #5 [hci0]
> > >      Vendor (0x3f|0x001e) ncmd 1
> > >       Status: Command Disallowed (0x0c)
> > >       05                                               .
> > >> HCI Event: Command Complete (0x0e) plen 4                   #6 [hci0]
> > >      Reset (0x03|0x0003) ncmd 2
> > >       Status: Success (0x00)
> > >
> > > Signed-off-by: Jesse Melhuish <melhuishj@chromium.org>
> > > Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
> > > Reviewed-by: Sonny Sasaka <sonnysasaka@chromium.org>
> > > ---
> > >
> > > Changes in v2:
> > > - Moved guard to the new home for this code.
> > >
> > > net/bluetooth/hci_sync.c | 6 ++++--
> > > 1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> > > index b794605dc882..5f1f59ac1813 100644
> > > --- a/net/bluetooth/hci_sync.c
> > > +++ b/net/bluetooth/hci_sync.c
> > > @@ -3887,8 +3887,10 @@ int hci_dev_open_sync(struct hci_dev *hdev)
> > >           hci_dev_test_flag(hdev, HCI_VENDOR_DIAG) && hdev->set_diag)
> > >               ret = hdev->set_diag(hdev, true);
> > >
> > > -     msft_do_open(hdev);
> > > -     aosp_do_open(hdev);
> > > +     if (!hci_dev_test_flag(hdev, HCI_USER_CHANNEL)) {
> > > +             msft_do_open(hdev);
> > > +             aosp_do_open(hdev);
> > > +     }
> >
> > but then you need to do the same on hci_dev_close. Also it would be good to extend userchan-tester with test cases for this.
> >
> > Regards
> >
> > Marcel
> >