Hi, Minchan,
2012/09/06 16:30, Minchan Kim wrote:
Hello Yasuaki,
On Thu, Sep 06, 2012 at 04:17:54PM +0900, Yasuaki Ishimatsu wrote:
Hi Minchan,
2012/09/06 14:16, 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));
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.
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
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)
When do the if statement, the page may be used by someone.
I can't understand your point.
We already hold zone->lock so that allocator and this function should be atomic
when the page is in free_list.
If I miss something, could you elaborate it more?
According to your description, the page might be allocated by someone
at this point. So some value might be set the page->index by the
intended purpose. Thus page->index has the potential to become
MIGRATE_ISOLATE value.
Thanks,
Yasuaki Ishimatsu
In this case, page->index may have some number. If the number is same as
MIGRATE_ISOLATE, the code goes worng.
Thanks,
Yasuaki Ishimatsu
pfn += 1;
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