Am Dienstag, den 05.01.2010, 00:43 -0700 schrieb Pete Zaitcev:
> 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;
This is the same patch as my. But __kfifo_len is renamed into kfifo_len.
Who should submit this patch?
Stefani
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