linux-kernel - bootmem: Double freeing a PFN on nodes spanning other nodes

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Message-ID: <87skwhyj8g.fsf@saeurebad.de>
Date:	Sat, 17 May 2008 00:30:55 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:	Linux MM Mailing List <linux-mm@...ck.org>
Subject: bootmem: Double freeing a PFN on nodes spanning other nodes

Hi,

When memory nodes overlap each other, the bootmem allocator is not aware
of this and might pass the same page twice to __free_pages_bootmem().

As I traced the code, this should result in bad_page() calls on every
boot but noone has yet reported something like this and I am wondering
why.

__free_pages_bootmem() boils down to either free_hot_cold_page() or
__free_one_page().  Either path should lead to setting the page private
or buddy:

free_hot_cold_page() sets ->private to the page block's migratetype (and
sets PG_private).

__free_one_page sets ->private to the page's order (and sets PG_private
and PG_buddy).

If a page is passed in twice, free_pages_check() should now warn (via
bad_page()) on the flags set above.

Am I missing something?  Thanks in advance.

	Hannes
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