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?
Yes. > > > 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 <[email protected]> > > Acked-by: Vlastimil Babka <[email protected]> Thanks, Vlastimil.
