[PATCH] mm/mmap.c: logic of find_vma_intersection repeated in __do_munmap

[PATCH] mm/mmap.c: logic of find_vma_intersection repeated in __do_munmap

[Gonzalo Matias Juarez Tello]

Logic of find_vma_intersection() (which is an inline fc) is
repeated in __do_munmap().
Besides, prev is assigned a value before checking vma->vm_start >= end
which might end up on a return statement making that assignment useless.

Calling find_vma_intersection() checks that condition and returns NULL if
no vma is found, hence only the !vma check is needed in __do_munmap().

Signed-off-by: Gonzalo Matias Juarez Tello <gmjuareztello@gmail.com>
---
 mm/mmap.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 3f287599a7a3..59ceaa474a00 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2822,16 +2822,11 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 	 */
 	arch_unmap(mm, start, end);
 
-	/* Find the first overlapping VMA */
-	vma = find_vma(mm, start);
+	/* Find the first overlapping VMA where start < vma->vm_end */
+	vma = find_vma_intersection(mm, start, end);
 	if (!vma)
 		return 0;
 	prev = vma->vm_prev;
-	/* we have  start < vma->vm_end  */
-
-	/* if it doesn't overlap, we have nothing.. */
-	if (vma->vm_start >= end)
-		return 0;
 
 	/*
 	 * If we need to split any vma, do it now to save pain later.
-- 
2.31.1

Re: [PATCH] mm/mmap.c: logic of find_vma_intersection repeated in __do_munmap

[Andrew Morton]

On Fri,  9 Apr 2021 13:21:26 -0300 Gonzalo Matias Juarez Tello <gmjuareztello@gmail.com> wrote:

> Logic of find_vma_intersection() (which is an inline fc) is
> repeated in __do_munmap().
> Besides, prev is assigned a value before checking vma->vm_start >= end
> which might end up on a return statement making that assignment useless.
> 
> Calling find_vma_intersection() checks that condition and returns NULL if
> no vma is found, hence only the !vma check is needed in __do_munmap().
> 
> ...
>
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2822,16 +2822,11 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
>  	 */
>  	arch_unmap(mm, start, end);
>  
> -	/* Find the first overlapping VMA */
> -	vma = find_vma(mm, start);
> +	/* Find the first overlapping VMA where start < vma->vm_end */
> +	vma = find_vma_intersection(mm, start, end);
>  	if (!vma)
>  		return 0;
>  	prev = vma->vm_prev;
> -	/* we have  start < vma->vm_end  */
> -
> -	/* if it doesn't overlap, we have nothing.. */
> -	if (vma->vm_start >= end)
> -		return 0;
>  
>  	/*
>  	 * If we need to split any vma, do it now to save pain later.

Looks good to me, thanks.