From ad53f92eb416d81e469fa8ea57153e59455e7175 Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Thu, 13 Nov 2014 15:19:11 -0800 Subject: mm/page_alloc: fix incorrect isolation behavior by rechecking migratetype Before describing bugs itself, I first explain definition of freepage. 1. pages on buddy list are counted as freepage. 2. pages on isolate migratetype buddy list are *not* counted as freepage. 3. pages on cma buddy list are counted as CMA freepage, too. Now, I describe problems and related patch. Patch 1: There is race conditions on getting pageblock migratetype that it results in misplacement of freepages on buddy list, incorrect freepage count and un-availability of freepage. Patch 2: Freepages on pcp list could have stale cached information to determine migratetype of buddy list to go. This causes misplacement of freepages on buddy list and incorrect freepage count. Patch 4: Merging between freepages on different migratetype of pageblocks will cause freepages accouting problem. This patch fixes it. Without patchset [3], above problem doesn't happens on my CMA allocation test, because CMA reserved pages aren't used at all. So there is no chance for above race. With patchset [3], I did simple CMA allocation test and get below result: - Virtual machine, 4 cpus, 1024 MB memory, 256 MB CMA reservation - run kernel build (make -j16) on background - 30 times CMA allocation(8MB * 30 = 240MB) attempts in 5 sec interval - Result: more than 5000 freepage count are missed With patchset [3] and this patchset, I found that no freepage count are missed so that I conclude that problems are solved. On my simple memory offlining test, these problems also occur on that environment, too. This patch (of 4): There are two paths to reach core free function of buddy allocator, __free_one_page(), one is free_one_page()->__free_one_page() and the other is free_hot_cold_page()->free_pcppages_bulk()->__free_one_page(). Each paths has race condition causing serious problems. At first, this patch is focused on first type of freepath. And then, following patch will solve the problem in second type of freepath. In the first type of freepath, we got migratetype of freeing page without holding the zone lock, so it could be racy. There are two cases of this race. 1. pages are added to isolate buddy list after restoring orignal migratetype CPU1 CPU2 get migratetype => return MIGRATE_ISOLATE call free_one_page() with MIGRATE_ISOLATE grab the zone lock unisolate pageblock release the zone lock grab the zone lock call __free_one_page() with MIGRATE_ISOLATE freepage go into isolate buddy list, although pageblock is already unisolated This may cause two problems. One is that we can't use this page anymore until next isolation attempt of this pageblock, because freepage is on isolate buddy list. The other is that freepage accouting could be wrong due to merging between different buddy list. Freepages on isolate buddy list aren't counted as freepage, but ones on normal buddy list are counted as freepage. If merge happens, buddy freepage on normal buddy list is inevitably moved to isolate buddy list without any consideration of freepage accouting so it could be incorrect. 2. pages are added to normal buddy list while pageblock is isolated. It is similar with above case. This also may cause two problems. One is that we can't keep these freepages from being allocated. Although this pageblock is isolated, freepage would be added to normal buddy list so that it could be allocated without any restriction. And the other problem is same as case 1, that it, incorrect freepage accouting. This race condition would be prevented by checking migratetype again with holding the zone lock. Because it is somewhat heavy operation and it isn't needed in common case, we want to avoid rechecking as much as possible. So this patch introduce new variable, nr_isolate_pageblock in struct zone to check if there is isolated pageblock. With this, we can avoid to re-check migratetype in common case and do it only if there is isolated pageblock or migratetype is MIGRATE_ISOLATE. This solve above mentioned problems. Changes from v3: Add one more check in free_one_page() that checks whether migratetype is MIGRATE_ISOLATE or not. Without this, abovementioned case 1 could happens. Signed-off-by: Joonsoo Kim Acked-by: Minchan Kim Acked-by: Michal Nazarewicz Acked-by: Vlastimil Babka Cc: "Kirill A. Shutemov" Cc: Mel Gorman Cc: Johannes Weiner Cc: Yasuaki Ishimatsu Cc: Zhang Yanfei Cc: Tang Chen Cc: Naoya Horiguchi Cc: Bartlomiej Zolnierkiewicz Cc: Wen Congyang Cc: Marek Szyprowski Cc: Laura Abbott Cc: Heesub Shin Cc: "Aneesh Kumar K.V" Cc: Ritesh Harjani Cc: Gioh Kim Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 11 +++++++++-- mm/page_isolation.c | 2 ++ 2 files changed, 11 insertions(+), 2 deletions(-) (limited to 'mm') diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9cd36b822444..df1da25b309b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -739,9 +739,16 @@ static void free_one_page(struct zone *zone, if (nr_scanned) __mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned); + if (unlikely(has_isolate_pageblock(zone) || + is_migrate_isolate(migratetype))) { + migratetype = get_pfnblock_migratetype(page, pfn); + if (is_migrate_isolate(migratetype)) + goto skip_counting; + } + __mod_zone_freepage_state(zone, 1 << order, migratetype); + +skip_counting: __free_one_page(page, pfn, zone, order, migratetype); - if (unlikely(!is_migrate_isolate(migratetype))) - __mod_zone_freepage_state(zone, 1 << order, migratetype); spin_unlock(&zone->lock); } diff --git a/mm/page_isolation.c b/mm/page_isolation.c index d1473b2e9481..1fa4a4d72ecc 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -60,6 +60,7 @@ out: int migratetype = get_pageblock_migratetype(page); set_pageblock_migratetype(page, MIGRATE_ISOLATE); + zone->nr_isolate_pageblock++; nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE); __mod_zone_freepage_state(zone, -nr_pages, migratetype); @@ -83,6 +84,7 @@ void unset_migratetype_isolate(struct page *page, unsigned migratetype) nr_pages = move_freepages_block(zone, page, migratetype); __mod_zone_freepage_state(zone, nr_pages, migratetype); set_pageblock_migratetype(page, migratetype); + zone->nr_isolate_pageblock--; out: spin_unlock_irqrestore(&zone->lock, flags); } -- cgit v1.2.3-58-ga151