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

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Message-ID: <e0b77a36-2d2b-735c-7a23-bbaab5adeba7@salutedevices.com>
Date: Thu, 19 Dec 2024 23:07:01 +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 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

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
> 
> 
>