Re: [PATCH 2/2] hso: fix deadlock when receiving bursts of data

[Dan Williams <dcbw@redhat.com>]

On Mon, 2014-07-07 at 11:06 +0200, Olivier Sobrie wrote:
> When the module sends bursts of data, sometimes a deadlock happens in
> the hso driver when the tty buffer doesn't get the chance to be flushed
> quickly enough.
> 
> To avoid this, first, we remove the endless while loop in
> put_rx_bufdata() which is the root cause of the deadlock.
> Secondly, when there is no room anymore in the tty buffer, we set up a
> timer of 100 msecs to give a chance to the upper layer to flush the tty
> buffer and make room for new data.

I assume this problem happens when using PPP for data transfer, instead
of using the network port that the modules expose?  Or maybe the NMEA
port?  I can't imagine that AT commands would make this happen...

Dan

> Signed-off-by: Olivier Sobrie <olivier@sobrie.be>
> ---
>  drivers/net/usb/hso.c |   51 +++++++++++++++++++++++++++++++++----------------
>  1 file changed, 35 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
> index 9ca2b41..1dff74f 100644
> --- a/drivers/net/usb/hso.c
> +++ b/drivers/net/usb/hso.c
> @@ -106,6 +106,8 @@
>  
>  #define MAX_RX_URBS			2
>  
> +#define UNTHROTTLE_TIMEOUT		100 /* msecs */
> +
>  /*****************************************************************************/
>  /* Debugging functions                                                       */
>  /*****************************************************************************/
> @@ -261,6 +263,7 @@ struct hso_serial {
>  	u16  curr_rx_urb_offset;
>  	u8   rx_urb_filled[MAX_RX_URBS];
>  	struct tasklet_struct unthrottle_tasklet;
> +	struct timer_list unthrottle_timer;
>  };
>  
>  struct hso_device {
> @@ -1161,13 +1164,18 @@ static void put_rxbuf_data_and_resubmit_bulk_urb(struct hso_serial *serial)
>  	while (serial->rx_urb_filled[serial->curr_rx_urb_idx]) {
>  		curr_urb = serial->rx_urb[serial->curr_rx_urb_idx];
>  		count = put_rxbuf_data(curr_urb, serial);
> -		if (count == -1)
> -			return;
>  		if (count == 0) {
>  			serial->curr_rx_urb_idx++;
>  			if (serial->curr_rx_urb_idx >= serial->num_rx_urbs)
>  				serial->curr_rx_urb_idx = 0;
>  			hso_resubmit_rx_bulk_urb(serial, curr_urb);
> +		} else if (count > 0) {
> +			mod_timer(&serial->unthrottle_timer,
> +				  jiffies
> +					+ msecs_to_jiffies(UNTHROTTLE_TIMEOUT));
> +			break;
> +		} else {
> +			break;
>  		}
>  	}
>  }
> @@ -1251,6 +1259,11 @@ static	void hso_unthrottle(struct tty_struct *tty)
>  	tasklet_hi_schedule(&serial->unthrottle_tasklet);
>  }
>  
> +static void hso_unthrottle_schedule(unsigned long data)
> +{
> +	tasklet_schedule((struct tasklet_struct *)data);
> +}
> +
>  /* open the requested serial port */
>  static int hso_serial_open(struct tty_struct *tty, struct file *filp)
>  {
> @@ -1286,6 +1299,10 @@ static int hso_serial_open(struct tty_struct *tty, struct file *filp)
>  		tasklet_init(&serial->unthrottle_tasklet,
>  			     (void (*)(unsigned long))hso_unthrottle_tasklet,
>  			     (unsigned long)serial);
> +		serial->unthrottle_timer.function = hso_unthrottle_schedule;
> +		serial->unthrottle_timer.data =
> +				(unsigned long)&serial->unthrottle_tasklet;
> +		init_timer(&serial->unthrottle_timer);
>  		result = hso_start_serial_device(serial->parent, GFP_KERNEL);
>  		if (result) {
>  			hso_stop_serial_device(serial->parent);
> @@ -1333,6 +1350,7 @@ static void hso_serial_close(struct tty_struct *tty, struct file *filp)
>  		tty_port_tty_set(&serial->port, NULL);
>  		if (!usb_gone)
>  			hso_stop_serial_device(serial->parent);
> +		del_timer_sync(&serial->unthrottle_timer);
>  		tasklet_kill(&serial->unthrottle_tasklet);
>  	}
>  
> @@ -2012,22 +2030,23 @@ static int put_rxbuf_data(struct urb *urb, struct hso_serial *serial)
>  
>  	tty = tty_port_tty_get(&serial->port);
>  
> +	if (tty && test_bit(TTY_THROTTLED, &tty->flags)) {
> +		tty_kref_put(tty);
> +		return -1;
> +	}
> +
>  	/* Push data to tty */
> -	write_length_remaining = urb->actual_length -
> -		serial->curr_rx_urb_offset;
>  	D1("data to push to tty");
> -	while (write_length_remaining) {
> -		if (tty && test_bit(TTY_THROTTLED, &tty->flags)) {
> -			tty_kref_put(tty);
> -			return -1;
> -		}
> -		curr_write_len = tty_insert_flip_string(&serial->port,
> -			urb->transfer_buffer + serial->curr_rx_urb_offset,
> -			write_length_remaining);
> -		serial->curr_rx_urb_offset += curr_write_len;
> -		write_length_remaining -= curr_write_len;
> -		tty_flip_buffer_push(&serial->port);
> -	}
> +	write_length_remaining = urb->actual_length -
> +					serial->curr_rx_urb_offset;
> +	curr_write_len =
> +		tty_insert_flip_string(&serial->port,
> +				       urb->transfer_buffer
> +						+ serial->curr_rx_urb_offset,
> +				       write_length_remaining);
> +	serial->curr_rx_urb_offset += curr_write_len;
> +	write_length_remaining -= curr_write_len;
> +	tty_flip_buffer_push(&serial->port);
>  	tty_kref_put(tty);
>  
>  	if (write_length_remaining == 0) {