Re: [PATCH 1/2] mm, page_alloc: Keep pcp count and list contents in sync if struct page is corrupted

[Vlastimil Babka]

On 12/02/2016 04:47 AM, Hillf Danton wrote:
> On Friday, December 02, 2016 8:23 AM Mel Gorman wrote:
> > Vlastimil Babka pointed out that commit 479f854a207c ("mm, page_alloc:
> > defer debugging checks of pages allocated from the PCP") will allow the
> > per-cpu list counter to be out of sync with the per-cpu list contents
> > if a struct page is corrupted. This patch keeps the accounting in sync.
> >
> > Fixes: 479f854a207c ("mm, page_alloc: defer debugging checks of pages allocated from the PCP")
> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> > cc: stable@xxxxxxxxxxxxxxx [4.7+]

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> > ---
> >  mm/page_alloc.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 6de9440e3ae2..777ed59570df 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2192,7 +2192,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
> >  			unsigned long count, struct list_head *list,
> >  			int migratetype, bool cold)
> >  {
> > -	int i;
> > +	int i, alloced = 0;
> >
> >  	spin_lock(&zone->lock);
> >  	for (i = 0; i < count; ++i) {
> > @@ -2217,13 +2217,14 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
> >  		else
> >  			list_add_tail(&page->lru, list);
> >  		list = &page->lru;
> > +		alloced++;
> >  		if (is_migrate_cma(get_pcppage_migratetype(page)))
> >  			__mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
> >  					      -(1 << order));
> >  	}
> >  	__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
>
> Now i is a pure index, yes?

No, even if a page fails the check_pcp_refill() check and is not 
"allocated", it is also no longer a free page, so it's correct to 
subtract it from NR_FREE_PAGES.

> >  	spin_unlock(&zone->lock);
> > -	return i;
> > +	return alloced;
> >  }
> >
> >  #ifdef CONFIG_NUMA
> > --
> > 2.10.2