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Subject[PATCH v3 3/4] memory-hotplug: bug fix race between isolation and allocation
Date
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));

This patch checks page's migratetype in freelist in __test_page_isolated_in_pageblock.
So now __test_page_isolated_in_pageblock can check the page caused by above race and
can fail of memory offlining.

* from v2
* Add Acked-by of Kame

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
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 87a7929..7ba7405 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -193,8 +193,11 @@ __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_freepage_migratetype(page) != MIGRATE_ISOLATE)
+ break;
pfn += 1 << page_order(page);
+ }
else if (page_count(page) == 0 &&
get_freepage_migratetype(page) == MIGRATE_ISOLATE)
pfn += 1;
--
1.7.9.5


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