linux-kernel - Re: [PATCH v2] Bluetooth: hci_uart: fix race during initialization

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Message-ID: <a2a239f1-5697-cb09-5e4f-83c024fd5ea6@salutedevices.com>
Date: Wed, 8 Jan 2025 15:39:04 +0300
From: Arseniy Krasnov <avkrasnov@...utedevices.com>
To: Luiz Augusto von Dentz <luiz.dentz@...il.com>
CC: Marcel Holtmann <marcel@...tmann.org>, <oxffffaa@...il.com>,
	<linux-bluetooth@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<kernel@...utedevices.com>
Subject: Re: [PATCH v2] Bluetooth: hci_uart: fix race during initialization



On 19.12.2024 23:07, Arseniy Krasnov wrote:
> 
> 
> On 19.12.2024 22:18, Luiz Augusto von Dentz wrote:
>> Hi Arseniy,
>>
>> On Tue, Dec 17, 2024 at 3:12 AM Arseniy Krasnov
>> <avkrasnov@...utedevices.com> wrote:
>>>
>>> 'hci_register_dev()' calls power up function, which is executed by
>>> kworker - 'hci_power_on()'. This function does access to bluetooth chip
>>> using callbacks from 'hci_ldisc.c', for example 'hci_uart_send_frame()'.
>>> Now 'hci_uart_send_frame()' checks 'HCI_UART_PROTO_READY' bit set, and
>>> if not - it fails. Problem is that 'HCI_UART_PROTO_READY' is set after
>>> 'hci_register_dev()', and there is tiny chance that 'hci_power_on()' will
>>> be executed before setting this bit. In that case HCI init logic fails.
>>>
>>> Patch moves setting of 'HCI_UART_PROTO_READY' before calling function
>>> 'hci_uart_register_dev()'.
>>>
>>> Signed-off-by: Arseniy Krasnov <avkrasnov@...utedevices.com>
>>> ---
>>>  Changelog v1->v2:
>>>  * Move 'set_bit()' before 'hci_uart_register_dev()' instead of
>>>    adding new bit 'HCI_UART_PROTO_INIT'.
>>
>> What drivers/controllers this was tested with? I want to make sure
>> this doesn't cause regressions to other drivers if there are perhaps
>> some drivers assuming HCI_UART_PROTO_READY was set in a certain order.
> 
> Hi,
> 
> I tested this on:
> 
> CONFIG_BT=y
> CONFIG_BT_HCIUART=y
> CONFIG_BT_HCIUART_H4=y

Hi, sorry, but is this enough info about my test env ?

Thanks

> 
> Yes, my v1 patchset with extra INIT bit was targeted to keep
> original behaviour - e.g. PROTO_READY bit usage still the same,
> just adding extra bit to handle this specific case.
> 
> Thanks
> 
>>
>>>  drivers/bluetooth/hci_ldisc.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
>>> index 30192bb083549..07b9aa09bbe2e 100644
>>> --- a/drivers/bluetooth/hci_ldisc.c
>>> +++ b/drivers/bluetooth/hci_ldisc.c
>>> @@ -704,12 +704,13 @@ static int hci_uart_set_proto(struct hci_uart *hu, int id)
>>>
>>>         hu->proto = p;
>>>
>>> +       set_bit(HCI_UART_PROTO_READY, &hu->flags);
>>> +
>>>         err = hci_uart_register_dev(hu);
>>>         if (err) {
>>>                 return err;
>>>         }
>>>
>>> -       set_bit(HCI_UART_PROTO_READY, &hu->flags);
>>>         return 0;
>>>  }
>>>
>>> --
>>> 2.30.1
>>
>>
>>