linux-kernel - Re: [rfc patch] wm8994: range checking issue

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Date:	Thu, 25 Mar 2010 13:58:22 +0300
From:	Dan Carpenter <error27@...il.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Liam Girdwood <lrg@...mlogic.co.uk>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [rfc patch] wm8994: range checking issue

On Wed, Mar 24, 2010 at 02:31:39PM +0000, Mark Brown wrote:
> On Wed, Mar 24, 2010 at 05:06:21PM +0300, Dan Carpenter wrote:
> > On Wed, Mar 24, 2010 at 12:59:46PM +0000, Mark Brown wrote:
> 
> > > This is caused by confusion with the MAX_CACHED_REGISTER definition in
> > > the header.  Best to use that one consistently, I guess - I've got a
> > > sneaking suspicion something has gone AWOL in the driver publication
> > > process.
> 
> > Hm...  That sounds more involved than I anticipated.  I don't have the
> > hardware and don't feel comfortable making complicated changes if I
> > can't test them.
> 
> Not really, it's just a case of picking the value to standardise on for
> the size of the array instead of the one you picked.  However, now I
> look at it again REG_CACHE_SIZE is the one we want and _MAX_CACHED_REGISTER 
> is bitrot which should be removed.
> 
> I didn't look as closely as I might due to the extraneous changes for
> BUG_ON() I mentioned which meant the patch wouldn't be applied anyway.
> Those shouldn't be changed because there's no way anything in the kernel
> should be generating a reference to a register which doesn't physically
> exist (which is what they check for).
> 
> > Can someone else take care of this.
> 
> Actually, now I look even more closely there's further issues with the
> patch - you're missing the fact that the register cache is only used for
> non-volatile registers but all registers beyond the end of the register
> cache are treated as volatile.  This means that I'm not convinced there
> are any actual problems here, I'm not sure what analysis smatch is doing
> but it looks to have generated false positives here.
> 

Yup.  You are right, this is a false positive.  I'm very sorry about that, 
I misread the code as well.

The problem is that Smatch doesn't do cross function analysis yet.  :/

regards,
dan carpenter

> I'll send a patch for _MAX_CACHED_REGISTER later today.
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