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Date: Sun, 1 Jun 2008 17:24:27 +0900
From: Paul Mundt <lethal@linux-sh.org>
To: Pekka J Enberg <penberg@cs.helsinki.fi>
Cc: David Howells <dhowells@redhat.com>, Christoph Lameter <clameter@sgi.com>,
       LKML <linux-kernel@vger.kernel.org>, cooloney@kernel.org,
       akpm@linux-foundation.org, mpm@selenic.com
Subject: Re: [PATCH] nommu: fix kobjsize() for SLOB and SLUB
Message-ID: <20080601082427.GC25429@linux-sh.org>
Mail-Followup-To: Paul Mundt <lethal@linux-sh.org>,
	Pekka J Enberg <penberg@cs.helsinki.fi>,
	David Howells <dhowells@redhat.com>,
	Christoph Lameter <clameter@sgi.com>,
	LKML <linux-kernel@vger.kernel.org>, cooloney@kernel.org,
	akpm@linux-foundation.org, mpm@selenic.com
References: <Pine.LNX.4.64.0805281646470.27125@sbz-30.cs.Helsinki.FI> <20080528153648.GA27783@linux-sh.org> <483DBA85.2060502@cs.helsinki.fi> <Pine.LNX.4.64.0805281325260.932@schroedinger.engr.sgi.com> <483DBFC3.1070108@cs.helsinki.fi> <29611.1212066517@redhat.com> <Pine.LNX.4.64.0805291620250.5415@sbz-30.cs.helsinki.fi> <20080529211207.GB13663@linux-sh.org> <484256AA.3000709@cs.helsinki.fi> <Pine.LNX.4.64.0806011119420.11749@sbz-30.cs.Helsinki.FI>
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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.