On 3/22/23 08:13, Lorenzo Stoakes wrote:
> Use find_vma_intersection() and vma_lookup() to both simplify the logic and
> to fold the end == next->vm_start condition into one block.
>
> This groups all of the simple range checks together and establishes the
> invariant that, if prev, curr or next are non-NULL then their positions are
> as expected.
>
> This has no functional impact.
I'm not so sure...
> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> ---
> mm/mmap.c | 24 +++++++++++-------------
> 1 file changed, 11 insertions(+), 13 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index c9834364ac98..dbdbb92493b2 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -930,15 +930,14 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
> if (vm_flags & VM_SPECIAL)
> return NULL;
>
> - curr = find_vma(mm, prev ? prev->vm_end : 0);
> - if (curr && curr->vm_end == end) /* cases 6, 7, 8 */
> - next = find_vma(mm, curr->vm_end);
> - else
> - next = curr;
> + /* Does the input range span an existing VMA? (cases 5 - 8) */
> + curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end);
>
> - /* In cases 1 - 4 there's no CCCC vma */
> - if (curr && end <= curr->vm_start)
> - curr = NULL;
> + if (!curr || /* cases 1 - 4 */
> + end == curr->vm_end) /* cases 6 - 8, adjacent VMA */
> + next = vma_lookup(mm, end);
AFAICS if the next vma is not adjacent to CCCC or ****, but there's a gap,
this will still give you a non-NULL result?
> + else
> + next = NULL; /* case 5 */
>
> /* verify some invariant that must be enforced by the caller */
> VM_WARN_ON(prev && addr <= prev->vm_start);
> @@ -959,11 +958,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
> }
> }
> /* Can we merge the successor? */
> - if (next && end == next->vm_start &&
And then without this end == next->vm_start check, merge will be done
despite the gap.
> - mpol_equal(policy, vma_policy(next)) &&
> - can_vma_merge_before(next, vm_flags,
> - anon_vma, file, pgoff+pglen,
> - vm_userfaultfd_ctx, anon_name)) {
> + if (next && mpol_equal(policy, vma_policy(next)) &&
> + can_vma_merge_before(next, vm_flags,
> + anon_vma, file, pgoff+pglen,
> + vm_userfaultfd_ctx, anon_name)) {
> merge_next = true;
> }
>
> --
> 2.39.2
