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Message-ID: <20161012053611.GB22174@techsingularity.net>
Date: Wed, 12 Oct 2016 06:36:11 +0100
From: Mel Gorman <mgorman@...hsingularity.net>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Sangseok Lee <sangseok.lee@....com>
Subject: Re: [PATCH 2/4] mm: prevent double decrease of nr_reserved_highatomic
On Fri, Oct 07, 2016 at 02:45:34PM +0900, Minchan Kim wrote:
> 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
> several 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: Mel Gorman <mgorman@...hsingularity.net>
--
Mel Gorman
SUSE Labs
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