linux-kernel - Re: [PATCH] Fix crash with FLAT_MEMORY and ARCH_PFN

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Date:	Mon, 7 Jan 2008 12:15:51 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:	linux-kernel@...r.kernel.org, Bob Picco <bob.picco@...com>,
	Dave Hansen <haveblue@...ibm.com>,
	Andy Whitcroft <apw@...dowen.org>, Andi Kleen <ak@....de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Keith Mannthey <kmannth@...il.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	akpm@...ux-foundation.org, Linus Torvalds <torvalds@...l.org>,
	ralf@...ux-mips.org
Subject: Re: [PATCH] Fix crash with FLAT_MEMORY and ARCH_PFN_OFFSET != 0

On (30/12/07 12:37), Thomas Bogendoerfer didst pronounce:
> On Thu, Dec 20, 2007 at 01:27:20PM +0000, Mel Gorman wrote:
> > On (20/12/07 13:43), Thomas Bogendoerfer didst pronounce:
> > > On Thu, Dec 20, 2007 at 11:44:06AM +0000, Mel Gorman wrote:
> > > > --- a/include/asm-mips/page.h
> > > > +++ b/include/asm-mips/page.h
> > > > @@ -37,13 +37,6 @@
> > > >  #include <linux/pfn.h>
> > > >  #include <asm/io.h>
> > > >  
> > > > -/*
> > > > - * It's normally defined only for FLATMEM config but it's
> > > > - * used in our early mem init code for all memory models.
> > > > - * So always define it.
> > > > - */
> > > > -#define ARCH_PFN_OFFSET		PFN_UP(PHYS_OFFSET)
> > > > -
> > > 
> > > hmm, doesn't this break what I've fixed ? Without this #define
> > > ARCH_PFN_OFFSET gets defined to 0 and the bug is back. Or did
> > > I miss anything ?
> > > 
> > 
> > ARCH_PFN_OFFSET goes to 0, so page_to_pfn() is no longer adjusting by
> > PFN_UP(PHYS_OFFSET) like it was when your problem occured. I am guessing
> > that the nature of the crash was that page_to_pfn() was returning bogus
> > values early in boot and trying to initialise memmap that didn't exist.
> 
> ic, your patch works for me.
> 

Grand. For the moment, your patch is the correct fix. This is a
micro-optimisation that can be picked up again at a later date. Thanks
for the testing and the fix.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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