On Mon, 04 Jan 2010 20:20:04 +0100
Stefani Seibold <stefani@xxxxxxxxxxx> wrote:
> Am Montag, den 04.01.2010, 18:43 +0100 schrieb Johan Hovold:
> > I noticed that the locking that used to protect kfifo_len in
> > usb_serial_generic_chars_in_buffer was removed when the kifo api changed
> > to not use internal locking (c1e13f25674ed564948ecb7dfe5f83e578892896 --
> > kfifo: move out spinlock).
> >
> > Was this intentional?
> >
>
> Yes, the locking is not necessary until only one reader and one writer
> is using the fifo. If you don't trust this you can apply this patch:
>
> --- linux-2.6.33-rc2.orig/drivers/usb/serial/generic.c 2009-12-27 23:37:03.566060210 +0100
> +++ linux-2.6.33-rc2.new/drivers/usb/serial/generic.c 2010-01-04 20:15:38.023351711 +0100
> @@ -386,12 +386,12 @@ int usb_serial_generic_chars_in_buffer(s
>
> dbg("%s - port %d", __func__, port->number);
>
> - if (serial->type->max_in_flight_urbs) {
> - spin_lock_irqsave(&port->lock, flags);
> + spin_lock_irqsave(&port->lock, flags);
> + if (serial->type->max_in_flight_urbs)
> chars = port->tx_bytes_flight;
> - spin_unlock_irqrestore(&port->lock, flags);
> - } else if (serial->num_bulk_out)
> + else if (serial->num_bulk_out)
> chars = kfifo_len(&port->write_fifo);
> + spin_unlock_irqrestore(&port->lock, flags);
>
> Then everything kfifo_... access in the usb serial is handled with an
> active spinlock.
This actually was a side effect of the "byte lost on close" patch
that I submitted, it should be in Greg's tree. The relevant part goes
like this:
diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index f1ea3a3..3372faa 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -386,12 +386,15 @@ int usb_serial_generic_chars_in_buffer(struct tty_struct *tty)
dbg("%s - port %d", __func__, port->number);
+ spin_lock_irqsave(&port->lock, flags);
if (serial->type->max_in_flight_urbs) {
- spin_lock_irqsave(&port->lock, flags);
chars = port->tx_bytes_flight;
- spin_unlock_irqrestore(&port->lock, flags);
- } else if (serial->num_bulk_out)
- chars = kfifo_len(&port->write_fifo);
+ } else if (serial->num_bulk_out) {
+ /* This overcounts badly, but is good enough for drain wait. */
+ chars = __kfifo_len(port->write_fifo);
+ chars += port->write_urb_busy * port->bulk_out_size;
+ }
+ spin_unlock_irqrestore(&port->lock, flags);
dbg("%s - returns %d", __func__, chars);
return chars;
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
