Re: [PATCH] Bluetooth: Ignore CC events not matching the last HCI command

["João Paulo Rechi Vita" <jprvita@gmail.com>]

On Wed, Apr 24, 2019 at 2:45 PM Marcel Holtmann <marcel@holtmann.org> wrote:
>
> Hi Joao Paulo,
>
> > This commit makes the kernel not send the next queued HCI command until
> > a command complete arrives for the last HCI command sent to the
> > controller. This change avoids a problem with some buggy controllers
> > (seen on two SKUs of QCA9377) that send an extra command complete event
> > for the previous command after the kernel had already sent a new HCI
> > command to the controller.
> >
> > The problem was reproduced when starting an active scanning procedure,
> > where an extra command complete event arrives for the LE_SET_RANDOM_ADDR
> > command. When this happends the kernel ends up not processing the
> > command complete for the following commmand, LE_SET_SCAN_PARAM, and
> > ultimately behaving as if a passive scanning procedure was being
> > performed, when in fact controller is performing an active scanning
> > procedure. This makes it impossible to discover BLE devices as no device
> > found events are sent to userspace.
> >
> > This problem is reproducible on 100% of the attempts on the affected
> > controllers. The extra command complete event can be seen at timestamp
> > 27.420131 on the btmon logs bellow.
> >
> > Bluetooth monitor ver 5.50
> > = Note: Linux version 5.0.0+ (x86_64)                                  0.352340
> > = Note: Bluetooth subsystem version 2.22                               0.352343
> > = New Index: 80:C5:F2:8F:87:84 (Primary,USB,hci0)               [hci0] 0.352344
> > = Open Index: 80:C5:F2:8F:87:84                                 [hci0] 0.352345
> > = Index Info: 80:C5:F2:8F:87:84 (Qualcomm)                      [hci0] 0.352346
> > @ MGMT Open: bluetoothd (privileged) version 1.14             {0x0001} 0.352347
> > @ MGMT Open: btmon (privileged) version 1.14                  {0x0002} 0.352366
> > @ MGMT Open: btmgmt (privileged) version 1.14                {0x0003} 27.302164
> > @ MGMT Command: Start Discovery (0x0023) plen 1       {0x0003} [hci0] 27.302310
> >        Address type: 0x06
> >          LE Public
> >          LE Random
> > < HCI Command: LE Set Random Address (0x08|0x0005) plen 6   #1 [hci0] 27.302496
> >        Address: 15:60:F2:91:B2:24 (Non-Resolvable)
> >> HCI Event: Command Complete (0x0e) plen 4                 #2 [hci0] 27.419117
> >      LE Set Random Address (0x08|0x0005) ncmd 1
> >        Status: Success (0x00)
> > < HCI Command: LE Set Scan Parameters (0x08|0x000b) plen 7  #3 [hci0] 27.419244
> >        Type: Active (0x01)
> >        Interval: 11.250 msec (0x0012)
> >        Window: 11.250 msec (0x0012)
> >        Own address type: Random (0x01)
> >        Filter policy: Accept all advertisement (0x00)
> >> HCI Event: Command Complete (0x0e) plen 4                 #4 [hci0] 27.420131
> >      LE Set Random Address (0x08|0x0005) ncmd 1
> >        Status: Success (0x00)
> > < HCI Command: LE Set Scan Enable (0x08|0x000c) plen 2      #5 [hci0] 27.420259
> >        Scanning: Enabled (0x01)
> >        Filter duplicates: Enabled (0x01)
> >> HCI Event: Command Complete (0x0e) plen 4                 #6 [hci0] 27.420969
> >      LE Set Scan Parameters (0x08|0x000b) ncmd 1
> >        Status: Success (0x00)
> >> HCI Event: Command Complete (0x0e) plen 4                 #7 [hci0] 27.421983
> >      LE Set Scan Enable (0x08|0x000c) ncmd 1
> >        Status: Success (0x00)
> > @ MGMT Event: Command Complete (0x0001) plen 4        {0x0003} [hci0] 27.422059
> >      Start Discovery (0x0023) plen 1
> >        Status: Success (0x00)
> >        Address type: 0x06
> >          LE Public
> >          LE Random
> > @ MGMT Event: Discovering (0x0013) plen 2             {0x0003} [hci0] 27.422067
> >        Address type: 0x06
> >          LE Public
> >          LE Random
> >        Discovery: Enabled (0x01)
> > @ MGMT Event: Discovering (0x0013) plen 2             {0x0002} [hci0] 27.422067
> >        Address type: 0x06
> >          LE Public
> >          LE Random
> >        Discovery: Enabled (0x01)
> > @ MGMT Event: Discovering (0x0013) plen 2             {0x0001} [hci0] 27.422067
> >        Address type: 0x06
> >          LE Public
> >          LE Random
> >        Discovery: Enabled (0x01)
> >
> > Signed-off-by: João Paulo Rechi Vita <jprvita@endlessm.com>
> > ---
> > net/bluetooth/hci_event.c | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index 609fd6871c5a..b349fc2b4123 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -3071,6 +3071,19 @@ static void hci_cmd_complete_evt(struct hci_dev *hdev, struct sk_buff *skb,
> >       *opcode = __le16_to_cpu(ev->opcode);
> >       *status = skb->data[sizeof(*ev)];
> >
> > +     if (*opcode != HCI_OP_RESET && !hci_sent_cmd_data(hdev, *opcode)) {
> > +             /* Some buggy controllers generate an extra command complete
> > +              * event for the previous command after a new commend was
> > +              * already sent, so if the opcode does not match the last sent
> > +              * command we should ignore this event.
> > +              *
> > +              * HCI_OP_RESET is a special case handled in
> > +              * hci_req_cmd_complete.
> > +              */
> > +             bt_dev_err(hdev, "unexpected CC event opcode 0x%4.4x", *opcode);
> > +             return;
> > +     }
> > +
>
> the return; here is not going to fly. You need to go through the switch statement since it actually does bookkeeping for a lot of features even if the command is not executed by hci_req and instead comes from user space or someone else.
>

Ok, so you want the same approach I had before but not bound to a
quirk. Sorry, when you previously said "ignore this command complete
and not start ahead with the next command" I thought you meant to also
avoid going through that switch statement.

> What is the problem with handling this in hci_req_cmd_complete. We have hci_sent_cmd_data check there already. Lets extend this to ensure that command complete for random commands don’t trigger us to continue with the request.
>

I'll send an updated revision soon.

--
João Paulo Rechi Vita
http://about.me/jprvita