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SubjectRe: [PATCH] Bluetooth: Ignore CC events not matching the last HCI command
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Hi Joao,

> 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>
> ---
> include/net/bluetooth/hci_core.h | 1 +
> net/bluetooth/hci_core.c | 5 +++++
> net/bluetooth/hci_event.c | 3 +++
> 3 files changed, 9 insertions(+)
>
> diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
> index 094e61e07030..85bed4e916d3 100644
> --- a/include/net/bluetooth/hci_core.h
> +++ b/include/net/bluetooth/hci_core.h
> @@ -364,6 +364,7 @@ struct hci_dev {
> struct sk_buff_head cmd_q;
>
> struct sk_buff *sent_cmd;
> + __u8 sent_cmd_pending_cc;

is there anything wrong with a bool type? And frankly using a flag seems more safe than just a boolean.

>
> struct mutex req_lock;
> wait_queue_head_t req_wait_q;
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index d6b2540ba7f8..37893b0c6077 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -4380,9 +4380,13 @@ void hci_req_cmd_complete(struct hci_dev *hdev, u16 opcode, u8 status,
> if (test_bit(HCI_INIT, &hdev->flags) && opcode == HCI_OP_RESET)
> hci_resend_last(hdev);
>
> + bt_dev_err(hdev,
> + "unexpected CC event for opcode 0x%4.4x", opcode);

Have you tested this? This will cause many error from tools like hciconfig or hcitool.

> return;
> }
>
> + hdev->sent_cmd_pending_cc = 0;
> +
> /* If the command succeeded and there's still more commands in
> * this request the request is not yet complete.
> */
> @@ -4493,6 +4497,7 @@ static void hci_cmd_work(struct work_struct *work)
>
> hdev->sent_cmd = skb_clone(skb, GFP_KERNEL);
> if (hdev->sent_cmd) {
> + hdev->sent_cmd_pending_cc = 1;
> atomic_dec(&hdev->cmd_cnt);
> hci_send_frame(hdev, skb);
> if (test_bit(HCI_RESET, &hdev->flags))

Fun part is actually that even commands injected via hcitool etc. will be added to the sent_cmd queue unless they are vendor specific commands. However some manufactures choose to use command complete for their vendor commands as well (others don’t).

> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index 609fd6871c5a..7541a4bc9444 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -3404,6 +3404,9 @@ static void hci_cmd_complete_evt(struct hci_dev *hdev, struct sk_buff *skb,
> hci_req_cmd_complete(hdev, *opcode, *status, req_complete,
> req_complete_skb);
>
> + if (hdev->sent_cmd_pending_cc)
> + return;
> +
> if (atomic_read(&hdev->cmd_cnt) && !skb_queue_empty(&hdev->cmd_q))
> queue_work(hdev->workqueue, &hdev->cmd_work);

I rather see this done super cleanly. We have a pending cmd request from the kernel, make sure it gets answered with the corresponding command complete or command status and not just some other event. If there is a command complete or command status for a command that we don’t have pending, then ignore.

Frankly, you are just hacking around here.

Regards

Marcel

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