linux-kernel - Re: [PATCH v1] Bluetooth: hci_uart: fix race during initialization

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Message-ID: <e18ebe28-e300-f9e3-ef66-1b7811ebd447@salutedevices.com>
Date: Mon, 16 Dec 2024 14:58:28 +0300
From: Arseniy Krasnov <avkrasnov@...utedevices.com>
To: Marcel Holtmann <marcel@...tmann.org>, Luiz Augusto von Dentz
	<luiz.dentz@...il.com>
CC: <linux-bluetooth@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<oxffffaa@...il.com>, <ddrokosov@...utedevices.com>
Subject: Re: [PATCH v1] Bluetooth: hci_uart: fix race during initialization

Hi, sorry, pls ping

Thanks

On 27.11.2024 15:38, Arseniy Krasnov 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 adds one more bit in addition to 'HCI_UART_PROTO_READY' which
> allows to perform power up logic without original bit set.
> 
> Signed-off-by: Arseniy Krasnov <avkrasnov@...utedevices.com>
> ---
>  drivers/bluetooth/hci_ldisc.c | 19 ++++++++++++++-----
>  drivers/bluetooth/hci_uart.h  |  1 +
>  2 files changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index 30192bb083549..2e20f00649bd7 100644
> --- a/drivers/bluetooth/hci_ldisc.c
> +++ b/drivers/bluetooth/hci_ldisc.c
> @@ -102,7 +102,8 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)
>  	if (!skb) {
>  		percpu_down_read(&hu->proto_lock);
>  
> -		if (test_bit(HCI_UART_PROTO_READY, &hu->flags))
> +		if (test_bit(HCI_UART_PROTO_READY, &hu->flags) ||
> +		    test_bit(HCI_UART_PROTO_INIT, &hu->flags))
>  			skb = hu->proto->dequeue(hu);
>  
>  		percpu_up_read(&hu->proto_lock);
> @@ -124,7 +125,8 @@ int hci_uart_tx_wakeup(struct hci_uart *hu)
>  	if (!percpu_down_read_trylock(&hu->proto_lock))
>  		return 0;
>  
> -	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags))
> +	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags) &&
> +	    !test_bit(HCI_UART_PROTO_INIT, &hu->flags))
>  		goto no_schedule;
>  
>  	set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
> @@ -278,7 +280,8 @@ static int hci_uart_send_frame(struct hci_dev *hdev, struct sk_buff *skb)
>  
>  	percpu_down_read(&hu->proto_lock);
>  
> -	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags)) {
> +	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags) &&
> +	    !test_bit(HCI_UART_PROTO_INIT, &hu->flags)) {
>  		percpu_up_read(&hu->proto_lock);
>  		return -EUNATCH;
>  	}
> @@ -582,7 +585,8 @@ static void hci_uart_tty_wakeup(struct tty_struct *tty)
>  	if (tty != hu->tty)
>  		return;
>  
> -	if (test_bit(HCI_UART_PROTO_READY, &hu->flags))
> +	if (test_bit(HCI_UART_PROTO_READY, &hu->flags) ||
> +	    test_bit(HCI_UART_PROTO_INIT, &hu->flags))
>  		hci_uart_tx_wakeup(hu);
>  }
>  
> @@ -608,7 +612,8 @@ static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data,
>  
>  	percpu_down_read(&hu->proto_lock);
>  
> -	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags)) {
> +	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags) &&
> +	    !test_bit(HCI_UART_PROTO_INIT, &hu->flags)) {
>  		percpu_up_read(&hu->proto_lock);
>  		return;
>  	}
> @@ -704,12 +709,16 @@ static int hci_uart_set_proto(struct hci_uart *hu, int id)
>  
>  	hu->proto = p;
>  
> +	set_bit(HCI_UART_PROTO_INIT, &hu->flags);
> +
>  	err = hci_uart_register_dev(hu);
>  	if (err) {
>  		return err;
>  	}
>  
>  	set_bit(HCI_UART_PROTO_READY, &hu->flags);
> +	clear_bit(HCI_UART_PROTO_INIT, &hu->flags);
> +
>  	return 0;
>  }
>  
> diff --git a/drivers/bluetooth/hci_uart.h b/drivers/bluetooth/hci_uart.h
> index 00bf7ae82c5b7..39f39704be41f 100644
> --- a/drivers/bluetooth/hci_uart.h
> +++ b/drivers/bluetooth/hci_uart.h
> @@ -89,6 +89,7 @@ struct hci_uart {
>  #define HCI_UART_REGISTERED		1
>  #define HCI_UART_PROTO_READY		2
>  #define HCI_UART_NO_SUSPEND_NOTIFIER	3
> +#define HCI_UART_PROTO_INIT		4
>  
>  /* TX states  */
>  #define HCI_UART_SENDING	1