On Thu, Mar 09, 2023 at 12:12:58PM +0100, Vlastimil Babka wrote:
> This effectively reverts d014cd7c1c35 ("mm, mremap: fix mremap()
> expanding for vma's with vm_ops->close()"). After the recent changes,
> vma_merge() is able to handle the expansion properly even when the vma
> being expanded has a vm_ops->close operation, so we don't need to
> special case it anymore.
>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> mm/mremap.c | 20 ++++----------------
> 1 file changed, 4 insertions(+), 16 deletions(-)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 411a85682b58..65f5b545601e 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -1040,23 +1040,11 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> * vma (expand operation itself) and possibly also with
> * the next vma if it becomes adjacent to the expanded
> * vma and otherwise compatible.
> - *
> - * However, vma_merge() can currently fail due to
> - * is_mergeable_vma() check for vm_ops->close (see the
> - * comment there). Yet this should not prevent vma
> - * expanding, so perform a simple expand for such vma.
> - * Ideally the check for close op should be only done
> - * when a vma would be actually removed due to a merge.
> */
> - if (!vma->vm_ops || !vma->vm_ops->close) {
> - vma = vma_merge(&vmi, mm, vma, extension_start,
> - extension_end, vma->vm_flags, vma->anon_vma,
> - vma->vm_file, extension_pgoff, vma_policy(vma),
> - vma->vm_userfaultfd_ctx, anon_vma_name(vma));
> - } else if (vma_expand(&vmi, vma, vma->vm_start,
> - addr + new_len, vma->vm_pgoff, NULL)) {
> - vma = NULL;
> - }
> + vma = vma_merge(&vmi, mm, vma, extension_start,
> + extension_end, vma->vm_flags, vma->anon_vma,
> + vma->vm_file, extension_pgoff, vma_policy(vma),
> + vma->vm_userfaultfd_ctx, anon_vma_name(vma));
> if (!vma) {
> vm_unacct_memory(pages);
> ret = -ENOMEM;
> --
> 2.39.2
>
Good to eliminate this edge case! Do we have a self-test for this case to assert
that the issue is fixed by this? I guess a little tricky due to the need for the
the owning VMA to have ->close() specified.
In any case, the changes you have made in the previous patch should ensure the
edge case is no longer required, hence:-
Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
