linux-kernel - [PATCH 4.9 03/77] mm: prevent double decrease of nr_reserved

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Date:   Sun, 24 Sep 2017 22:31:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Sangseok Lee <sangseok.lee@....com>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Miles Chen <miles.chen@...iatek.com>
Subject: [PATCH 4.9 03/77] mm: prevent double decrease of nr_reserved_highatomic

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

------------------

From: Minchan Kim <minchan@...nel.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@...nel.org>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: Mel Gorman <mgorman@...hsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Sangseok Lee <sangseok.lee@....com>
Cc: Michal Hocko <mhocko@...e.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Miles Chen <miles.chen@...iatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2100,13 +2100,25 @@ static void unreserve_highatomic_pageblo
 				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