[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <1476259429-18279-3-git-send-email-minchan@kernel.org>
Date: Wed, 12 Oct 2016 17:03:47 +0900
From: Minchan Kim <minchan@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>,
Vlastimil Babka <vbabka@...e.cz>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Sangseok Lee <sangseok.lee@....com>,
Michal Hocko <mhocko@...e.com>,
Minchan Kim <minchan@...nel.org>
Subject: [PATCH v3 2/4] mm: prevent double decrease of nr_reserved_highatomic
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.
Signed-off-by: Minchan Kim <minchan@...nel.org>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: Mel Gorman <mgorman@...hsingularity.net>
---
mm/page_alloc.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 79853b258211..18808f392718 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2106,13 +2106,25 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
continue;
/*
- * 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
--
2.7.4
Powered by blists - more mailing lists