linux-kernel - Re: [PATCH v3] mm/mmap: Don't unlock VMAs in remap_file

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Date:   Wed, 24 Feb 2021 11:13:39 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Liam Howlett <liam.howlett@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v3] mm/mmap: Don't unlock VMAs in remap_file_pages()

On 24.02.21 00:50, Liam Howlett wrote:
> Since this call uses MAP_FIXED, do_mmap() will munlock the necessary
> range.  There is also an error in the loop test expression which will
> evaluate as false and the loop body has never execute.
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> Acked-by: Hugh Dickins <hughd@...gle.com>
> ---
>   mm/mmap.c | 18 +-----------------
>   1 file changed, 1 insertion(+), 17 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index dc7206032387c..e22b048733269 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3025,25 +3025,9 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
>   
>   	flags &= MAP_NONBLOCK;
>   	flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE;
> -	if (vma->vm_flags & VM_LOCKED) {
> -		struct vm_area_struct *tmp;
> +	if (vma->vm_flags & VM_LOCKED)
>   		flags |= MAP_LOCKED;
>   
> -		/* drop PG_Mlocked flag for over-mapped range */
> -		for (tmp = vma; tmp->vm_start >= start + size;
> -				tmp = tmp->vm_next) {
> -			/*
> -			 * Split pmd and munlock page on the border
> -			 * of the range.
> -			 */
> -			vma_adjust_trans_huge(tmp, start, start + size, 0);
> -
> -			munlock_vma_pages_range(tmp,
> -					max(tmp->vm_start, start),
> -					min(tmp->vm_end, start + size));
> -		}
> -	}
> -
>   	file = get_file(vma->vm_file);
>   	ret = do_mmap(vma->vm_file, start, size,
>   			prot, flags, pgoff, &populate, NULL);
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb