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

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Date:   Mon, 10 Aug 2020 08:57:55 +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 10:28pm, Wei Yang wrote:
> 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()?

Yeah, it's fine to me.

> 
> >>  	list_del(&nrg->link);
> >>  
> >> -- 
> >> 2.20.1 (Apple Git-117)
> >> 
> >> 
> 
> -- 
> Wei Yang
> Help you, Help me
>