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    SubjectRe: USB: serial: kfifo_len locking
    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



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