[PATCH 3.17 027/141] mm/page_alloc: fix incorrect isolation behavior by rechecking migratetype

From: Greg Kroah-Hartman
Date: Wed Nov 19 2014 - 17:36:44 EST

3.17-stable review patch. If anyone has any objections, please let me know.


From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

commit ad53f92eb416d81e469fa8ea57153e59455e7175 upstream.

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

- 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


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 <iamjoonsoo.kim@xxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Cc: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
Cc: Tang Chen <tangchen@xxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Cc: Wen Congyang <wency@xxxxxxxxxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
Cc: Heesub Shin <heesub.shin@xxxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Ritesh Harjani <ritesh.list@xxxxxxxxx>
Cc: Gioh Kim <gioh.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

include/linux/mmzone.h | 9 +++++++++
include/linux/page-isolation.h | 8 ++++++++
mm/page_alloc.c | 11 +++++++++--
mm/page_isolation.c | 2 ++
4 files changed, 28 insertions(+), 2 deletions(-)

--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -431,6 +431,15 @@ struct zone {
int nr_migrate_reserve_block;

+ /*
+ * Number of isolated pageblock. It is used to solve incorrect
+ * freepage counting problem due to racy retrieving migratetype
+ * of pageblock. Protected by zone->lock.
+ */
+ unsigned long nr_isolate_pageblock;
/* see spanned/present_pages for more description */
seqlock_t span_seqlock;
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -2,6 +2,10 @@

+static inline bool has_isolate_pageblock(struct zone *zone)
+ return zone->nr_isolate_pageblock;
static inline bool is_migrate_isolate_page(struct page *page)
return get_pageblock_migratetype(page) == MIGRATE_ISOLATE;
@@ -11,6 +15,10 @@ static inline bool is_migrate_isolate(in
return migratetype == MIGRATE_ISOLATE;
+static inline bool has_isolate_pageblock(struct zone *zone)
+ return false;
static inline bool is_migrate_isolate_page(struct page *page)
return false;
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -740,9 +740,16 @@ static void free_one_page(struct zone *z
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);
__free_one_page(page, pfn, zone, order, migratetype);
- if (unlikely(!is_migrate_isolate(migratetype)))
- __mod_zone_freepage_state(zone, 1 << order, migratetype);

--- 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 pa
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--;
spin_unlock_irqrestore(&zone->lock, flags);

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