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

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Date:   Fri, 2 Dec 2016 07:19:16 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hillf Danton <hillf.zj@...baba-inc.com>,
        'Mel Gorman' <mgorman@...hsingularity.net>,
        'Andrew Morton' <akpm@...ux-foundation.org>
Cc:     'Christoph Lameter' <cl@...ux.com>,
        'Michal Hocko' <mhocko@...e.com>,
        'Johannes Weiner' <hannes@...xchg.org>,
        'Jesper Dangaard Brouer' <brouer@...hat.com>,
        'Linux-MM' <linux-mm@...ck.org>,
        'Linux-Kernel' <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm, page_alloc: Keep pcp count and list contents in
 sync if struct page is corrupted

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@...e.de>
>> cc: stable@...r.kernel.org [4.7+]

Acked-by: Vlastimil Babka <vbabka@...e.cz>

>> ---
>>  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
>