Re: [PATCH 28/28] mm, page_alloc: Defer debugging checks of pages allocated from the PCP

[Vlastimil Babka]

On 05/17/2016 08:41 AM, Naoya Horiguchi wrote:
>> @@ -2579,20 +2612,22 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
>>   		struct list_head *list;
>>   
>>   		local_irq_save(flags);
>> -		pcp = &this_cpu_ptr(zone->pageset)->pcp;
>> -		list = &pcp->lists[migratetype];
>> -		if (list_empty(list)) {
>> -			pcp->count += rmqueue_bulk(zone, 0,
>> -					pcp->batch, list,
>> -					migratetype, cold);
>> -			if (unlikely(list_empty(list)))
>> -				goto failed;
>> -		}
>> +		do {
>> +			pcp = &this_cpu_ptr(zone->pageset)->pcp;
>> +			list = &pcp->lists[migratetype];
>> +			if (list_empty(list)) {
>> +				pcp->count += rmqueue_bulk(zone, 0,
>> +						pcp->batch, list,
>> +						migratetype, cold);
>> +				if (unlikely(list_empty(list)))
>> +					goto failed;
>> +			}
>>   
>> -		if (cold)
>> -			page = list_last_entry(list, struct page, lru);
>> -		else
>> -			page = list_first_entry(list, struct page, lru);
>> +			if (cold)
>> +				page = list_last_entry(list, struct page, lru);
>> +			else
>> +				page = list_first_entry(list, struct page, lru);
>> +		} while (page && check_new_pcp(page));
> 
> This causes infinite loop when check_new_pcp() returns 1, because the bad
> page is still in the list (I assume that a bad page never disappears).
> The original kernel is free from this problem because we do retry after
> list_del(). So moving the following 3 lines into this do-while block solves
> the problem?
> 
>      __dec_zone_state(zone, NR_ALLOC_BATCH);
>      list_del(&page->lru);
>      pcp->count--;
> 
> There seems no infinit loop issue in order > 0 block below, because bad pages
> are deleted from free list in __rmqueue_smallest().

Ooops, thanks for catching this, wish it was sooner...

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