memory-hotplug: bug fix race between isolation and allocation
Minchan Kim [Mon, 8 Oct 2012 23:32:14 +0000 (16:32 -0700)]
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@kernel.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_isolation.c

index 9c03dca..6744235 100644 (file)
@@ -200,8 +200,11 @@ __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;