linux-kernel - Re: [PATCH] mm: Change count_mm_mlocked_page

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Message-ID: <20190513091522.GA30100@dhcp22.suse.cz>
Date:   Mon, 13 May 2019 11:15:22 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Weikang shi <swkhack@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Change count_mm_mlocked_page_nr return type

On Mon 13-05-19 10:37:01, Weikang shi wrote:
> From: swkhack <swkhack@...il.com>
> 
> In 64-bit machine,the value of "vma->vm_end - vma->vm_start"
> maybe negative in 32bit int and the "count >> PAGE_SHIFT"'s result
> will be wrong.So change the local variable and return
> value to unsigned long will fix the problem.
> 
> Signed-off-by: swkhack <swkhack@...il.com>

Fixes: 0cf2f6f6dc60 ("mm: mlock: check against vma for actual mlock() size")

Acked-by: Michal Hocko <mhocko@...e.com>

Most users probably never noticed because large mlocked areas are not
allowed by default. So I am not really sure this is worth backporting to
stable trees.

> ---
>  mm/mlock.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 080f3b364..d614163f5 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -636,11 +636,11 @@ static int apply_vma_lock_flags(unsigned long start, size_t len,
>   * is also counted.
>   * Return value: previously mlocked page counts
>   */
> -static int count_mm_mlocked_page_nr(struct mm_struct *mm,
> +static unsigned long count_mm_mlocked_page_nr(struct mm_struct *mm,
>  		unsigned long start, size_t len)
>  {
>  	struct vm_area_struct *vma;
> -	int count = 0;
> +	unsigned long count = 0;
>  
>  	if (mm == NULL)
>  		mm = current->mm;
> -- 
> 2.17.1

-- 
Michal Hocko
SUSE Labs