Re: USB: serial: kfifo_len locking

[Johan Hovold <jhovold@gmail.com>]

On Tue, Jan 05, 2010 at 12:09:19PM +0100, Stefani Seibold wrote:
> Am Dienstag, den 05.01.2010, 12:04 +0100 schrieb Johan Hovold:
> > > 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;
> > 
> > That is indeed what you submitted on Dec 7, but this is what is in
> > Greg's tree:
> > 
> > http://git.kernel.org/?p=linux/kernel/git/gregkh/patches.git;a=blob;f=usb/usb-serial-mct_usb232-add-drain-on-close.patch;h=c464f1a82e93df0dd41762a8cb33b0b22e90cdd7;hb=1ea72e7c40b239c6b6f88a4993196be66fc3d892
> > 
> > 38 --- a/drivers/usb/serial/generic.c
> > 39 +++ b/drivers/usb/serial/generic.c
> > 40 @@ -369,8 +369,11 @@ int usb_serial_generic_write_room(struct
> > 41                         room = port->bulk_out_size *
> > 42                                 (serial->type->max_in_flight_urbs -
> > 43                                  port->urbs_in_flight);
> > 44 -       } else if (serial->num_bulk_out)
> > 45 +       } else if (serial->num_bulk_out) {
> > 46 +               /* This overcounts badly, but is good enough for drain wait. */
> > 47                 room = kfifo_avail(&port->write_fifo);
> > 48 +               room += port->write_urb_busy * port->bulk_out_size;
> > 49 +       }
> > 50         spin_unlock_irqrestore(&port->lock, flags);
> > 51  
> > 52         dbg("%s - returns %d", __func__, room);
> > 
> > 
> > Which does not make any sense at all. Bad merge? What do you say Greg?
> > 
> 
> I don't know where is your problem? This are two different functions
> usb_serial_generic_write_room() and usb_serial_generic_chars_in_buffer()

Exactly my point. 

The drain patch needed to modify chars_in_buffer, but the patch in Greg's
tree modifies write_room instead (which does not make sense and was
neither part of the submitted patch).

/Johan