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

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Date:   Fri, 7 Aug 2020 20:49:51 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>
Cc:     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 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);
>  	list_del(&nrg->link);
>  
> -- 
> 2.20.1 (Apple Git-117)
> 
>