Re: [PATCH] mm, hotplug: protect nr_zones with pgdat_resize_lock()

[Michal Hocko <mhocko@suse.com>]

On Thu 22-11-18 01:52:39, Wei Yang wrote:
> On Wed, Nov 21, 2018 at 08:15:49AM +0100, Michal Hocko wrote:
[...]
> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >index c6c42a7425e5..c75fca900044 100644
> >--- a/mm/memory_hotplug.c
> >+++ b/mm/memory_hotplug.c
> >@@ -743,13 +743,12 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
> > 	int nid = pgdat->node_id;
> > 	unsigned long flags;
> > 
> >+	/* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */
> >+	pgdat_resize_lock(pgdat, &flags);
> > 	if (zone_is_empty(zone))
> > 		init_currently_empty_zone(zone, start_pfn, nr_pages);
> > 
> > 	clear_zone_contiguous(zone);
> >-
> >-	/* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */
> >-	pgdat_resize_lock(pgdat, &flags);
> > 	zone_span_writelock(zone);
> 
> Just want to make sure, Oscar suggests to move the code here to protect
> this under zone_span_lock.

Yes, both locks held is probably safer. Because there is both pgdat and
zone state updated.

Sorry to confuse you

-- 
Michal Hocko
SUSE Labs