linux-kernel - Re: [PATCH] usb-serial regression (Oops) in 2.6.21-rc*

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Date:	Mon, 12 Mar 2007 15:42:35 -0700
From:	Jim Radford <radford@...ckbean.org>
To:	Greg KH <greg@...ah.com>
Cc:	Mark Lord <lkml@....ca>, linux-usb-devel@...ts.sourceforge.net,
	Oliver Neukum <oneukum@...e.de>, Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb-serial regression (Oops)  in 2.6.21-rc*

On Mon, Mar 12, 2007 at 01:33:31PM -0700, Greg KH wrote:
> On Mon, Mar 12, 2007 at 04:22:22PM -0400, Mark Lord wrote:
> > Oliver Neukum wrote:
> > >>Mark Lord wrote:
> > >>>Okay, from that part (above), the problem is obvious:
> > >>>in that the "MCT U232 converter now disconnected" appears,
> > >>>and then we continue to try and call the driver's method.. Oops!

> > >IMHO shutdown() is using serial->port[] and bombs.
> > >Could you reverse the order here?

> > Yup.  Fixed.  Tested.  Works.

> > This patch fixes the Oops that otherwise occurs whenever
> > a USB serial adapter is unplugged from a system, as well
> > the Oops seen when one is in use before resume (to RAM).

> Argh, no, this change was done to help the ftdi drivers out.

> Look at changeset d9a7ecacac5f8274d2afce09aadcf37bdb42b93a in Linus's
> tree from Jim Radford:
> 	http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=d9a7ecacac5f8274d2afce09aadcf37bdb42b93a
> 
> It makes this change because the usb-serial drivers need the port
> devices when the port_remove() callbacks happen.  Otherwise you get an
> oops that way.

> Jim, can you take a look at this and see if you can figure something
> out?

The problem is really the

   serial->port[i] = NULL;

line after device_unregister() which is used to flag "fake" devices
that don't need legacy cleanup later in the destrol_serial.  That
flagging should be done using a *real* flag, and not by overloading
the ->port[i] pointer since we require it to be non-NULL in
->shutdown() in all drivers that are not converted to new
->port_probe()/->port_remove() framework (currently all except ftdi).

I'll work on a patch to do that, but for now, I think you should apply
Mark's patch to revert the order change since the FTDI driver no
longer requires the correct ordering of device_unregister() and
->shutdown().

-Jim
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