linux-kernel - Re: [PATCH 02/10] mm/hugetlb: make sure to get NULL when list is empty

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Message-ID: <20200807142800.GA14692@L-31X9LVDL-1304.local>
Date:   Fri, 7 Aug 2020 22:28:00 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Wei Yang <richard.weiyang@...ux.alibaba.com>,
        mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/10] mm/hugetlb: make sure to get NULL when list is
 empty

On Fri, Aug 07, 2020 at 08:49:51PM +0800, Baoquan He wrote:
>On 08/07/20 at 05:12pm, Wei Yang wrote:
>> list_first_entry() may not return NULL even when the list is empty.
>> 
>> Let's make sure the behavior by using list_first_entry_or_null(),
>> otherwise it would corrupt the list.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@...ux.alibaba.com>
>> ---
>>  mm/hugetlb.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 62ec74f6d03f..0a2f3851b828 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -237,7 +237,8 @@ get_file_region_entry_from_cache(struct resv_map *resv, long from, long to)
>>  	VM_BUG_ON(resv->region_cache_count <= 0);
>
>
>We have had above line, is it possible to be NULL from list_first_entry?
>
>>  
>>  	resv->region_cache_count--;
>> -	nrg = list_first_entry(&resv->region_cache, struct file_region, link);
>> +	nrg = list_first_entry_or_null(&resv->region_cache,
>> +			struct file_region, link);
>>  	VM_BUG_ON(!nrg);

Or we can remove this VM_BUG_ON()?

>>  	list_del(&nrg->link);
>>  
>> -- 
>> 2.20.1 (Apple Git-117)
>> 
>> 

-- 
Wei Yang
Help you, Help me