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

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

(2012/07/23 9:48), Minchan Kim 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@kernel.org>

Ah, hm. Then, you say the page in MIGRATE_MOVABLE will not be isolated
and may be used again.


> ---
> 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)) {
> +			if (get_page_migratetype(page) != MIGRATE_ISOLATE)
> +				break;

Doesn't this work enough ? The problem is MIGRATE_TYPE and list_head mis-match.

Thanks,
-Kame
 


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