linux-kernel - Re: [PATCH 1/2] drivers/telephony/ixj.c::add_caps(): don't rely on undefined behaviour

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Date:	Tue, 20 Mar 2012 06:51:43 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Jesper Juhl <jj@...osbits.net>
Cc:	Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Ed Okerson <eokerson@...cknet.net>,
	Greg Herlein <gherlein@...cknet.net>,
	"David W. Erhart" <derhart@...cknet.net>,
	John Sellers <jsellers@...cknet.net>,
	Mike Preston <mpreston@...cknet.net>,
	David Huggins-Daines <dhd@...stral.com>,
	Fabio Ferrari <fabio.ferrari@...itro.com.br>,
	Artis Kugevics <artis@...lv>,
	Daniele Bellucci <bellucda@...cali.it>
Subject: Re: [PATCH 1/2] drivers/telephony/ixj.c::add_caps(): don't rely on
 undefined behaviour

On Tue, Mar 20, 2012 at 12:40:50AM +0100, Jesper Juhl wrote:
> On Mon, 19 Mar 2012, Joe Perches wrote:
> 
> > On Tue, 2012-03-20 at 00:19 +0100, Jesper Juhl wrote:
> > > On Mon, 19 Mar 2012, Joe Perches wrote:
> > > > On Mon, 2012-03-19 at 23:46 +0100, Jesper Juhl wrote:
> > > > > On Mon, 19 Mar 2012, Joe Perches wrote:
> > > > > > On Mon, 2012-03-19 at 23:37 +0100, Jesper Juhl wrote:
> > > > > > > In drivers/telephony/ixj.c::add_caps() we have several statements like this:
> > > > > > >   	j->caplist[j->caps].handle = j->caps++;
> > > > > > > That's undefined behaviour right there.
> > > > > > telephony has been moved to staging.
> > > > > Since when? Where?
> > > > > In my up-to-date Linus tree with HEAD at 
> > > > > c16fa4f2ad19908a47c63d8fa436a1178438c7e7, that file is is still in 
> > > > > drivers/telephony/, not in staging/...
> > > > > /confused
> > > > In the -next tree.
> > > Ok, seems I've missed that.
> > > > Yes, it's a bug fix, but drivers/telephony is pretty dead.
> > > Dead or not, as long as it's in the tree I think that fixing bugs is 
> > > relevant.
> > > Besides, who knows if/when it'll get ressurrected ;)
> > 
> > Sorry, I didn't mean to suggest it shouldn't
> > be fixed.
> > 
> > I meant that it probably didn't need to be
> > fixed during the merge window or maybe even
> > not backported to stable unless you're sure
> > the order of operations is now done correctly
> > and with no real change in current operation
> > by inspecting the object.  I presume it worked
> > before but it's likely not too many people
> > actually still use this hardware with the
> > current kernel.
> > 
> I never intended to push it for -stable, it probably "works" in its 
> current form with any relevant compiler. I just spotted a bug and wanted 
> to fix it :-)
> If it gets fixed during the merge window or at some other time I don't 
> really care - but I don't see any reason to not just fix it as soon as 
> possible.
> 
> I have no idea how many people still use this hardware with current 
> kernels, but even if just a few do, they deserve to get code that has 
> well-defined behaviour with standards conforming C compilers and not what 
> is currently there that can change with different compilers/different 
> compiler versions.

Then care to send me the patch, against the linux-next tree, so I can
queue it up for the 3.5 merge window?

greg k-h
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