On Fri, Jul 27, 2012 at 07:22:48PM +0900, Kamezawa Hiroyuki wrote:

(2012/07/23 9:48), Minchan Kim wrote:

quoted

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.

Yes.

quoted

---
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.

I guess you are confused between get_page_migratetype and get_pageblock_migratetype.
It's not get_pageblock_migratetype but get_page_migratetype which is introduced for detecting
MIGRATE_TYPE and list_head mismatch in [1,2/3].

Thanks,
-Kame
 

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