Re: [PATCH 01/22] mm: Add vma_lookup()

Davidlohr Bueso
2021-05-21T03:32:54Z

On Mon, 10 May 2021, Liam Howlett wrote:

>Many places in the kernel use find_vma() to get a vma and then check the
>start address of the vma to ensure the next vma was not returned.
>
>Other places use the find_vma_intersection() call with add, addr + 1 as
>the range; looking for just the vma at a specific address.
>
>The third use of find_vma() is by developers who do not know that the
>function starts searching at the provided address upwards for the next
>vma. This results in a bug that is often overlooked for a long time.
>
>Adding the new vma_lookup() function will allow for cleaner code by
>removing the find_vma() calls which check limits, making
>find_vma_intersection() calls of a single address to be shorter, and
>potentially reduce the incorrect uses of find_vma().
>
>Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
>---
> include/linux/mm.h | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
>diff --git a/include/linux/mm.h b/include/linux/mm.h
>index 25b9041f9925..5f2a15e702ff 100644
>--- a/include/linux/mm.h
>+++ b/include/linux/mm.h
>@@ -2689,6 +2689,24 @@ static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * m
> return vma;
> }

While at it can we clean up find_vma_intersection? I'm not particularly
user/fan of checkpatch.pl, but this one is kind of ridiculous.

Thanks,
Davidlohr

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c274f75efcf9..16eddedf783f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2678,9 +2678,14 @@ extern struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long add
extern struct vm_area_struct * find_vma_prev(struct mm_struct * mm, unsigned long addr,
struct vm_area_struct **pprev);

-/* Look up the first VMA which intersects the interval start_addr..end_addr-1,
- NULL if none. Assume start_addr < end_addr. */
-static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * mm, unsigned long start_addr, unsigned long end_addr)
+/*
+ * Look up the first VMA which intersects the interval start_addr..end_addr-1,
+ * NULL if none. Assume start_addr < end_addr.
+ */
+static inline
+struct vm_area_struct *find_vma_intersection(struct mm_struct * mm,
+ unsigned long start_addr,
+ unsigned long end_addr)
{
struct vm_area_struct * vma = find_vma(mm,start_addr);