Commit 39f56772 authored Dec 12, 2016 by Minchan Kim Committed by Greg Kroah-Hartman Sep 27, 2017

mm: prevent double decrease of nr_reserved_highatomic

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>

parent f609266b

mm/page_alloc.c

+18 −6

Original line number	Diff line number	Diff line
		@@ -2100,13 +2100,25 @@ 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.
		*/
		zone->nr_reserved_highatomic -= min(pageblock_nr_pages,
		* 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.
		*/
		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