[PATCH 4.4 16/66] mm: prevent double decrease of nr_reserved_highatomic

Greg Kroah-Hartman
2017-09-24T20:34:29Z

From: Minchan Kim <minchan@kernel.org>

commit 4855e4a7f29d6d10b0b9c84e189c770c9a94e91e upstream.

There is race between page freeing and unreserved highatomic.

CPU 0 CPU 1

free_hot_cold_page
mt = get_pfnblock_migratetype
set_pcppage_migratetype(page, mt)
unreserve_highatomic_pageblock
spin_lock_irqsave(&zone->lock)
move_freepages_block
set_pageblock_migratetype(page)
spin_unlock_irqrestore(&zone->lock)
free_pcppages_bulk
__free_one_page(mt) <- mt is stale

By above race, a page on CPU 0 could go non-highorderatomic free list
since the pageblock's type is changed. By that, unreserve logic of
highorderatomic can decrease reserved count on a same pageblock severak
times and then it will make mismatch between nr_reserved_highatomic and
the number of reserved pageblock.

So, this patch verifies whether the pageblock is highatomic or not and
decrease the count only if the pageblock is highatomic.

Link: http://lkml.kernel.org/r/1476259429-18279-3-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Sangseok Lee <sangseok.lee@lge.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miles Chen <miles.chen@mediatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/page_alloc.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1748,13 +1748,25 @@ static void unreserve_highatomic_pageblo
struct page, lru);

/*
- * It should never happen but changes to locking could
- * inadvertently allow a per-cpu drain to add pages
- * to MIGRATE_HIGHATOMIC while unreserving so be safe
- * and watch for underflows.
+ * In page freeing path, migratetype change is racy so
+ * we can counter several free pages in a pageblock
+ * in this loop althoug we changed the pageblock type
+ * from highatomic to ac->migratetype. So we should
+ * adjust the count once.
*/
- zone->nr_reserved_highatomic -= min(pageblock_nr_pages,
- zone->nr_reserved_highatomic);
+ if (get_pageblock_migratetype(page) ==
+ MIGRATE_HIGHATOMIC) {
+ /*
+ * It should never happen but changes to
+ * locking could inadvertently allow a per-cpu
+ * drain to add pages to MIGRATE_HIGHATOMIC
+ * while unreserving so be safe and watch for
+ * underflows.
+ */
+ zone->nr_reserved_highatomic -= min(
+ pageblock_nr_pages,
+ zone->nr_reserved_highatomic);
+ }

/*
* Convert to ac->migratetype and avoid the normal