linux-kernel - Re: [PATCH] nommu: fix kobjsize() for SLOB and SLUB

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Message-ID: <20080601082427.GC25429@linux-sh.org>
Date:	Sun, 1 Jun 2008 17:24:27 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Pekka J Enberg <penberg@...helsinki.fi>
Cc:	David Howells <dhowells@...hat.com>,
	Christoph Lameter <clameter@....com>,
	LKML <linux-kernel@...r.kernel.org>, cooloney@...nel.org,
	akpm@...ux-foundation.org, mpm@...enic.com
Subject: Re: [PATCH] nommu: fix kobjsize() for SLOB and SLUB

On Sun, Jun 01, 2008 at 11:22:04AM +0300, Pekka J Enberg wrote:
> On Sun, 1 Jun 2008, Pekka Enberg wrote:
> > > Not until the page->index bits are killed, otherwise you aren't fixing
> > > anything. SLOB on nommu with those page->index tests will automatically
> > > oops today, before or after your patches. Until that's resolved, there's
> > > no point in pretending like kobjsize() has been "fixed". As no one has
> > > come up with a valid reason for those tests existing in the first place,
> > > simply having your patches and killing the BUG_ON()'s seems ok.
> > 
> > Sorry if I'm starting to sound like a broken record, but can you explain why
> > removing the ->index bits are safe? I mean, if removing them is really okay,
> > that means we don't hit that code path with SLAB at all?
> 
> Paul, so with something like this, the WARN_ON never triggers?
> 
> diff --git a/mm/nommu.c b/mm/nommu.c
> index dca93fc..38eec2e 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -109,16 +109,23 @@ unsigned int kobjsize(const void *objp)
>  	 * If the object we have should not have ksize performed on it,
>  	 * return size of 0
>  	 */
> -	if (!objp || (unsigned long)objp >= memory_end || !((page = virt_to_page(objp))))
> +	if (!objp)
> +		return 0;
> +
> +	if ((unsigned long)objp >= memory_end)
> +		return 0;
> +
> +	page = virt_to_page(objp);
> +	if (!page)
>  		return 0;
>  
This still needs to be virt_to_head_page() I think.

I don't have my nommu boards at home, so I'll test at the office tomorow
morning and let you know.
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