linux-kernel - Re: memory_hotplug: always initialize pageblock bitmap.

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Message-ID: <20080513185242.GA6465@osiris.boeblingen.de.ibm.com>
Date:	Tue, 13 May 2008 20:52:42 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andy Whitcroft <apw@...dowen.org>,
	Dave Hansen <haveblue@...ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: memory_hotplug: always initialize pageblock bitmap.

On Tue, May 13, 2008 at 01:58:25PM +0200, Heiko Carstens wrote:
> From: Heiko Carstens <heiko.carstens@...ibm.com>
> 
> Trying to online a new memory section that was added via memory hotplug
> sometimes results in crashes when the new pages are added via __free_page.
> Reason for that is that the pageblock bitmap isn't initialized and hence
> contains random stuff.  That means that get_pageblock_migratetype() returns
> also random stuff and therefore
> 
> 	list_add(&page->lru,
> 		&zone->free_area[order].free_list[migratetype]);
> 
> in __free_one_page() tries to do a list_add to something that isn't even
> necessarily a list.
> 
> This happens since 86051ca5eaf5e560113ec7673462804c54284456
> ("mm: fix usemap initialization") which makes sure that the pageblock
> bitmap gets only initialized for pages present in a zone.
> Unfortunately for hot-added memory the zones "grow" after the memmap
> and the pageblock memmap have been initialized. Which means that the
> new pages have an unitialized bitmap.
> To solve this the calls to grow_zone_span() and grow_pgdat_span() are
> moved to __add_zone() just before the initialization happens.
> 
> The patch also moves the two functions since __add_zone() is the only
> caller and I didn't want to add a forward declaration.
> 
> Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
> Cc: Andy Whitcroft <apw@...dowen.org>
> Cc: Dave Hansen <haveblue@...ibm.com>
> Cc: Gerald Schaefer <gerald.schaefer@...ibm.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Yasunori Goto <y-goto@...fujitsu.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---

Oops... the patch is tested and works for me. However it was not Signed-off
by Andrew. And in addition I forgot to add [PATCH] to the subject.
Sorry about that!

If all agree that this patch is ok it should probably also go into
-stable, since it fixes the above mentioned regression.
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