[PATCH] mm: __count_immobile_pages make sure the node is online

[Michal Hocko]

On Thu 12-01-12 18:33:23, KAMEZAWA Hiroyuki wrote:
[...]
> > From 04f74e6f0ebf28f61650d63f8884e8855fb21b55 Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@xxxxxxx>
> > Date: Thu, 12 Jan 2012 10:19:04 +0100
> > Subject: [PATCH] mm: __count_immobile_pages make sure the node is online
> > 
> > page_zone requires to have an online node otherwise we are accessing
> > NULL NODE_DATA. This is not an issue at the moment because node_zones
> > are located at the structure beginning but this might change in the
> > future so better be careful about that.
> > 
> > Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > ---
> >  mm/page_alloc.c |   11 +++++++++--
> >  1 files changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 485be89..c6fb8ea 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5607,14 +5607,21 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
> >  
> >  bool is_pageblock_removable_nolock(struct page *page)
> >  {
> > -	struct zone *zone = page_zone(page);
> > -	unsigned long pfn = page_to_pfn(page);
> > +	struct zone *zone;
> > +	unsigned long pfn;
> >  
> >  	/*
> >  	 * We have to be careful here because we are iterating over memory
> >  	 * sections which are not zone aware so we might end up outside of
> >  	 * the zone but still within the section.
> > +	 * We have to take care about the node as well. If the node is offline
> > +	 * its NODE_DATA will be NULL - see page_zone.
> >  	 */
> > +	if (!node_online(page_to_nid(page)))
> > +		return false;
> > +
> > +	zone = page_zone(page);
> > +	pfn = page_to_pfn(page);
> >  	if (!zone || zone->zone_start_pfn > pfn ||
> >  			zone->zone_start_pfn + zone->spanned_pages <= pfn)
> >  		return false;
> 
> !zone check can be removed because of node_online() check.

Yes you are right. Fixed bellow:
---