Re: [PATCH 2/4] mm: prevent double decrease of nr_reserved_highatomic
From: Minchan Kim
Date: Fri Oct 07 2016 - 10:46:06 EST
On Fri, Oct 07, 2016 at 02:44:15PM +0200, Vlastimil Babka wrote:
> On 10/07/2016 07:45 AM, Minchan Kim wrote:
> >There is race between page freeing and unreserved highatomic.
> > CPU 0 CPU 1
> > free_hot_cold_page
> > mt = get_pfnblock_migratetype
> so here mt == MIGRATE_HIGHATOMIC?
> > 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.
> Hmm I see.
> >So, this patch verifies whether the pageblock is highatomic or not
> >and decrease the count only if the pageblock is highatomic.
> Yeah I guess that's the easiest solution.
> >Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>