Re: mm: compaction: Check for overlapping nodes during isolation for migration

["Michal Nazarewicz" <mina86@mina86.com>]

On Mon, 06 Feb 2012 10:08:41 +0100, Mel Gorman <mgorman@suse.de> wrote:
> When isolating pages for migration, migration starts at the start of a
> zone while the free scanner starts at the end of the zone. Migration
> avoids entering a new zone by never going beyond the free scanned.
> Unfortunately, in very rare cases nodes can overlap. When this happens,
> migration isolates pages without the LRU lock held, corrupting lists
> which will trigger errors in reclaim or during page free such as in the
> following oops
[...]
> The fix is straight-forward. isolate_migratepages() has to make a
> similar check to isolate_freepage to ensure that it never isolates
> pages from a zone it does not hold the LRU lock for.
>
> This was discovered in a 3.0-based kernel but it affects 3.1.x, 3.2.x
> and current mainline.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>

Acked-by: Michal Nazarewicz <mina86@mina86.com>

> Cc: <stable@vger.kernel.org>
> ---
>  mm/compaction.c |   11 ++++++++++-
>  1 files changed, 10 insertions(+), 1 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index bd6e739..6042644 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -330,8 +330,17 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>  			continue;
>  		nr_scanned++;
>-		/* Get the page and skip if free */
> +		/*
> +		 * Get the page and ensure the page is within the same zone.
> +		 * See the comment in isolate_freepages about overlapping
> +		 * nodes. It is deliberate that the new zone lock is not taken
> +		 * as memory compaction should not move pages between nodes.
> +		 */
>  		page = pfn_to_page(low_pfn);
> +		if (page_zone(page) != zone)
> +			continue;
> +
> +		/* Skip if free */
>  		if (PageBuddy(page))
>  			continue;
>

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@google.com>--------------ooO--(_)--Ooo--

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