linux-kernel - Re: [PATCH v2 09/11] mm/migration: fix potential page refcounts leak in migrate

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Date:   Fri, 18 Mar 2022 16:24:28 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Feng Tang <feng.tang@...el.com>
CC:     <ziy@...dia.com>, <baolin.wang@...ux.alibaba.com>,
        <ying.huang@...el.com>, <songmuchun@...edance.com>,
        <apopple@...dia.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 09/11] mm/migration: fix potential page refcounts leak
 in migrate_pages

On 2022/3/18 15:08, Feng Tang wrote:
>> In -ENOMEM case, there might be some subpages of fail-to-migrate THPs
>> left in thp_split_pages list. We should move them back to migration
>> list so that they could be put back to the right list by the caller
>> otherwise the page refcnt will be leaked here. Also adjust nr_failed
>> and nr_thp_failed accordingly to make vm events account more accurate.
>  
> We just met a real world case for this when checking a malloc-oom
> issue and our fix is similar with yours :).
> 

Oh, what a coincidence! :)

> So I think you can remove the 'potential' from the patch subject.
> Feel free to add
> 
> Tested-by: Feng Tang <feng.tang@...el.com>
> Reviewed-by: Feng Tang <feng.tang@...el.com>

Many thanks for your test and comment!

> 
> Thanks,
> Feng
> 
>> Fixes: b5bade978e9b ("mm: migrate: fix the return value of migrate_pages()")
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> Reviewed-by: Zi Yan <ziy@...dia.com>
>> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
>> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> ---
>>  mm/migrate.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 63a87ef0996f..97dfd1f4870d 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1438,6 +1438,14 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>  				}
>>  
>>  				nr_failed_pages += nr_subpages;
>> +				/*
>> +				 * There might be some subpages of fail-to-migrate THPs
>> +				 * left in thp_split_pages list. Move them back to migration
>> +				 * list so that they could be put back to the right list by
>> +				 * the caller otherwise the page refcnt will be leaked.
>> +				 */
>> +				list_splice_init(&thp_split_pages, from);
>> +				nr_thp_failed += thp_retry;
>>  				goto out;
>>  			case -EAGAIN:
>>  				if (is_thp)
>> -- 
>> 2.23.0
> 
> .
>