linux-kernel - Re: [RFC 3/3] memory-hotplug: bug fix race between isolation and allocation

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Date:	Tue, 17 Jul 2012 18:13:17 +0800
From:	Bob Liu <lliubbo@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [RFC 3/3] memory-hotplug: bug fix race between isolation and allocation

Hi Minchan,

On Tue, Jul 17, 2012 at 3:01 PM, Minchan Kim <minchan@...nel.org> wrote:
> Like below, memory-hotplug makes race between page-isolation
> and page-allocation so it can hit BUG_ON in __offline_isolated_pages.
>
>         CPU A                                   CPU B
>
> start_isolate_page_range
> set_migratetype_isolate
> spin_lock_irqsave(zone->lock)
>
>                                 free_hot_cold_page(Page A)
>                                 /* without zone->lock */
>                                 migratetype = get_pageblock_migratetype(Page A);
>                                 /*
>                                  * Page could be moved into MIGRATE_MOVABLE
>                                  * of per_cpu_pages
>                                  */
>                                 list_add_tail(&page->lru, &pcp->lists[migratetype]);
>
> set_pageblock_isolate
> move_freepages_block
> drain_all_pages
>
>                                 /* Page A could be in MIGRATE_MOVABLE of free_list. */
>
> check_pages_isolated
> __test_page_isolated_in_pageblock
> /*
>  * We can't catch freed page which
>  * is free_list[MIGRATE_MOVABLE]
>  */
> if (PageBuddy(page A))
>         pfn += 1 << page_order(page A);
>
>                                 /* So, Page A could be allocated */
>
> __offline_isolated_pages
> /*
>  * BUG_ON hit or offline page
>  * which is used by someone
>  */
> BUG_ON(!PageBuddy(page A));
>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> I found this problem during code review so please confirm it.
> Kame?
>
>  mm/page_isolation.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index acf65a7..4699d1f 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -196,8 +196,11 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn)
>                         continue;
>                 }
>                 page = pfn_to_page(pfn);
> -               if (PageBuddy(page))
> +               if (PageBuddy(page)) {
>                         pfn += 1 << page_order(page);
> +                       if (get_page_migratetype(page) != MIGRATE_ISOLATE)
> +                               break;
> +               }

test_page_isolated() already have check
get_pageblock_migratetype(page) != MIGRATE_ISOLATE.

>                 else if (page_count(page) == 0 &&
>                                 get_page_migratetype(page) == MIGRATE_ISOLATE)
>                         pfn += 1;
> --
> 1.7.9.5
>


-- 
Regards,
--Bob
--
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