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    Subject[56/67] USB: serial: fix stalled writes
    2.6.35-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Johan Hovold <jhovold@gmail.com>

    commit b58af4066d240b18b43f202e07b9ec7461d90b17 upstream.

    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@cisco.com>
    Tested-by: David VomLehn <dvomlehn@cisco.com>
    Signed-off-by: Johan Hovold <jhovold@gmail.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/usb/serial/generic.c | 15 ++++++++++-----
    1 file changed, 10 insertions(+), 5 deletions(-)

    --- 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). */



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