Re: linux-next: manual merge of the mm tree with Linus' tree

Matthew Wilcox
2023-07-27T23:50:04Z

On Fri, Jul 28, 2023 at 09:18:49AM +1000, Stephen Rothwell wrote:
> diff --cc mm/memory.c
> index ca632b58f792,271982fab2b8..000000000000
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@@ -5392,32 -5597,18 +5597,21 @@@ retry
> if (!vma)
> goto inval;
>
> - /* Only anonymous and tcp vmas are supported for now */
> - if (!vma_is_anonymous(vma) && !vma_is_tcp(vma))
> - /* find_mergeable_anon_vma uses adjacent vmas which are not locked */
> - if (vma_is_anonymous(vma) && !vma->anon_vma)
> -- goto inval;
> --
> if (!vma_start_read(vma))
> goto inval;
>
> + /*
> + * find_mergeable_anon_vma uses adjacent vmas which are not locked.
> + * This check must happen after vma_start_read(); otherwise, a
> + * concurrent mremap() with MREMAP_DONTUNMAP could dissociate the VMA
> + * from its anon_vma.
> + */
> - if (unlikely(!vma->anon_vma && !vma_is_tcp(vma)))
> - goto inval_end_read;
> -
> - /*
> - * Due to the possibility of userfault handler dropping mmap_lock, avoid
> - * it for now and fall back to page fault handling under mmap_lock.
> - */
> - if (userfaultfd_armed(vma))
> ++ if (unlikely(vma_is_anonymous(vma) && !vma_is_tcp(vma)))
> + goto inval_end_read;
> +

No, this isn't right. It should be:

if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma))
goto inval_end_read;

I'm not sure about the userfaultfd_armed() clause. My patch wasn't
intended to affect that.

> /* Check since vm_start/vm_end might change before we lock the VMA */
> - if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
> - vma_end_read(vma);
> - goto inval;
> - }
> + if (unlikely(address < vma->vm_start || address >= vma->vm_end))
> + goto inval_end_read;
>
> /* Check if the VMA got isolated after we found it */
> if (vma->detached) {