linux-kernel - Re: [PATCH] MM: Fix NR_SECTION_ROOTS == 0 when using using sparsemem extreme.

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Date:	Thu, 20 May 2010 01:14:47 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	mroberto@...i.cetuc.puc-rio.br
Cc:	akpm@...ux-foundation.org, kosaki.motohiro@...fujitsu.com,
	cl@...ux-foundation.org, mel@....ul.ie, minchan.kim@...il.com,
	linux@....linux.org.uk, sfr@...b.auug.org.au, hpa@...or.com,
	yinghai@...nel.org, sshtylyov@...sta.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] MM: Fix NR_SECTION_ROOTS == 0 when using using
 sparsemem extreme.

On Wed,  5 May 2010 18:02:46 -0300, Marcelo Roberto Jimenez <mroberto@...i.cetuc.puc-rio.br> wrote:
> Got this while compiling for ARM/SA1100:
> 
> mm/sparse.c: In function '__section_nr':
> mm/sparse.c:135: warning: 'root' is used uninitialized in this function
> 
> This patch follows Russell King's suggestion for a new calculation for
> NR_SECTION_ROOTS. Thanks also to Sergei Shtylyov for pointing out the
> existence of the macro DIV_ROUND_UP.

JFYI, This fix is not just silence the warning, fix a real problem.

Without this fix, mem_section[] might have 0 size so mem_section[0]
will share other variable area.  For example, I got:

c030c700 b __warned.16478
c030c700 B mem_section
c030c701 b __warned.16483

This might cause very strange behavior.  Your patch actually fixes it.
Thank you.

---
Atsushi Nemoto
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