linux-kernel - Re: [Bug 8473] New: Oops: 0010 [1] SMP

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Date:	Fri, 08 Jun 2007 09:10:57 -0500
From:	Paul Fulghum <paulkf@...rogate.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Björn Steinbrink <B.Steinbrink@....de>,
	Arnd Bergmann <arnd@...db.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Nicolas Mailhot <nicolas.mailhot@...oste.net>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	"bugme-daemon@...nel-bugs.osdl.org" 
	<bugme-daemon@...zilla.kernel.org>, linux-kernel@...r.kernel.org,
	Mel Gorman <mel@....ul.ie>,
	Christoph Lameter <clameter@....com>
Subject: Re: [Bug 8473] New: Oops: 0010 [1] SMP

On Thu, 2007-06-07 at 20:16 -0700, Andrew Morton wrote:
> On Fri, 8 Jun 2007 05:06:29 +0200 Björn Steinbrink <B.Steinbrink@....de> wrote:
> > This is do_tty_hangup() exchanging the fops while we're waiting for the
> > lock. The new fops (hung_up_tty_fops) only have the unlocked variant and
> > thus we Oops our way.
> 
> ah, yes, that explains it, thanks.  Culprit:
> 
> commit e10cc1df1d2014f68a4bdcf73f6dd122c4561f94
> Author: Paul Fulghum <paulkf@...rogate.com>
> Date:   Thu May 10 22:22:50 2007 -0700
> 
>     tty: add compat_ioctl
>     
>     Add compat_ioctl method for tty code to allow processing of 32 bit ioctl
>     calls on 64 bit systems by tty core, tty drivers, and line disciplines.

OK, the change of hung_up_tty_ioctl() from locked to unlocked
is not necessary for this patch. On the surface it seemed a clever
way of not needing two different functions to do the same simple:

return cmd == TIOCSPGRP ? -ENOTTY : -EIO;

which does not need any locking for its own sake. But clearly
the hangup behavior requires the locked version.

I'll redo the patch with hung_up_tty_ioctl remaining locked.

That will separate the compat ioctl stuff from this issue.

-- 
Paul Fulghum
Microgate Systems, Ltd

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