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Date: Wed, 23 Nov 2011 21:59:09 +0000
From: Alan Cox <alan@linux.intel.com>
To: Havard Skinnemoen <hskinnemoen@google.com>
Cc: Jiri Slaby <jslaby@suse.cz>, Dave Jones <davej@redhat.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@suse.de>, Jiri Slaby <jirislaby@gmail.com>
Subject: Re: [RFC] cdc-acm: Fix potential deadlock (lockdep warning)
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On Wed, 23 Nov 2011 13:03:27 -0800
Havard Skinnemoen <hskinnemoen@google.com> wrote:

> On Wed, Nov 23, 2011 at 11:44 AM, Alan Cox <alan@linux.intel.com>
> wrote:
> > Any data owned by the USB part needs to be handled by the USB
> > driver. In the case of usb-serial it keeps its own krefs for that
> > because the lifetime of the port/USB serial data is not the same as
> > the lifetime of the tty itself.
> 
> Yes, exactly. But since tty_port already has a kref, why not use that?
> It doesn't have any other use currently.

Indeed
 
> Hmm, a quick grep tells me tty_port_get() and tty_port_put() are
> completely unused. What was the intention behind them?

To provide a way to use the kref nicely.