linux-kernel - Re: USB: serial: kfifo

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Date:	Tue, 5 Jan 2010 13:10:59 +0100
From:	Johan Hovold <jhovold@...il.com>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	Johan Hovold <jhovold@...il.com>,
	Pete Zaitcev <zaitcev@...hat.com>, Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: USB: serial: kfifo_len locking

> > Here's the change. The fifo used to be protected by a lock, but is no
> > longer.
>  
> I posted yesterday a patch to this thread. It would be great if you read
> and check this patch before complaining again!!!!
> 
> > Never say you did.
> 
> Sorry, i had no real idea what is your problem, if this is not what you
> want. As i mentioned i posted to you yesterday a fix for the possible
> kfifo_len() bug, but i didn't get a response if this is fixing your
> problem. Again the patch:
> 
> diff -u -N -r  -p linux-2.6.33-rc2.orig/drivers/usb/serial/generic.c linux-2.6.33-rc2.new/drivers/usb/serial/generic.c
> --- 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);
>  
>  	dbg("%s - returns %d", __func__, chars);
>  	return chars;
> 
> This patch should solve the possible race (if there is one). With this
> patch all kfifo_... access are locked by the port->lock spinlock. If
> this is what you want i will posted it as a bug fix to andrew.

Yes, please do.

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