On Wed, Aug 04, 2010 at 03:45:57PM +0200, Johan Hovold wrote:
> As David VomLehn points out, it was possible to receive an interrupt
> before clearing the free-urb flag which could lead to the urb being
> incorrectly marked as busy.
>
> For the same reason, move tx_bytes accounting so that it will never be
> negative.
>
> Note that the free-flags set and clear operations do not need any
> additional locking as they are manipulated while USB_SERIAL_WRITE_BUSY
> is set.
>
> Reported-by: David VomLehn <dvomlehn@xxxxxxxxx>
> Signed-off-by: Johan Hovold <jhovold@xxxxxxxxx>
> ---
>
> Hi,
>
> I was able to trigger the bug David identified by simply inserting a delay
> after submit_urb, and I have also verified that the patch below solves the
> problem.
>
> Note that the set/clear bit operations below do not need any additional
> locking as the write-busy flag is set.
>
> Thanks,
> Johan
>
> drivers/usb/serial/generic.c | 15 ++++++++++-----
> 1 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
> index a817ced..ca92f67 100644
> --- a/drivers/usb/serial/generic.c
> +++ b/drivers/usb/serial/generic.c
> @@ -208,18 +208,23 @@ retry:
> urb->transfer_buffer_length = count;
> usb_serial_debug_data(debug, &port->dev, __func__, count,
> urb->transfer_buffer);
> + spin_lock_irqsave(&port->lock, flags);
> + port->tx_bytes += count;
> + spin_unlock_irqrestore(&port->lock, flags);
> +
> + clear_bit(i, &port->write_urbs_free);
> result = usb_submit_urb(urb, GFP_ATOMIC);
> if (result) {
> dev_err(&port->dev, "%s - error submitting urb: %d\n",
> __func__, result);
> + set_bit(i, &port->write_urbs_free);
> + spin_lock_irqsave(&port->lock, flags);
> + port->tx_bytes -= count;
> + spin_unlock_irqrestore(&port->lock, flags);
> +
> clear_bit_unlock(USB_SERIAL_WRITE_BUSY, &port->flags);
> return result;
> }
> - clear_bit(i, &port->write_urbs_free);
> -
> - spin_lock_irqsave(&port->lock, flags);
> - port->tx_bytes += count;
> - spin_unlock_irqrestore(&port->lock, flags);
>
> /* Try sending off another urb, unless in irq context (in which case
> * there will be no free urb). */
> --
> 1.7.1.1
>
This works great for me. Feel free to add:
Tested-by: David VomLehn <dvomlehn@xxxxxxxxx>
--
David VL
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