linux-kernel - Re: [PATCH] nommu: fix kobjsize() for SLOB and SLUB, v2.

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Date:	Tue, 10 Jun 2008 10:30:36 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Paul Mundt <lethal@...ux-sh.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	David Howells <dhowells@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, cooloney@...nel.org,
	mpm@...enic.com
Subject: Re: [PATCH] nommu: fix kobjsize() for SLOB and SLUB, v2.

On Mon, 2 Jun 2008, Paul Mundt wrote:

> +	page = virt_to_head_page(objp);
> +	if (!page)
> +		return 0;

virt_to_head_page cannot return NULL. virt_to_page also does not return 
NULL. pfn_valid() needs to be used to figure out if a page is valid. 
Otherwise the page struct reference that was returned may have 
PageReserved() set to indicate that it is not a valid page.

> +	 * The ksize() function is only guaranteed to work for pointers
> +	 * returned by kmalloc(). So handle arbitrary pointers, that we expect
> +	 * always to be compound pages, here.
> +	 */
> +	if (PageCompound(page))
> +		order = compound_order(page);

compund order returns 0 if you use compound_order() on a 
non compound page. No need for the PageCompound test.

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