linux-kernel - Re: USB: serial: kfifo

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Date:	Tue, 5 Jan 2010 12:04:18 +0100
From:	Johan Hovold <jhovold@...il.com>
To:	Pete Zaitcev <zaitcev@...hat.com>, Greg KH <greg@...ah.com>
Cc:	Stefani Seibold <stefani@...bold.net>,
	Johan Hovold <jhovold@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: USB: serial: kfifo_len locking

> 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?

/Johan

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