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

Stephen Rothwell
2023-07-27T23:29:24Z

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Hi all,

On Fri, 28 Jul 2023 09:18:49 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
>
> Today's linux-next merge of the mm tree got a conflict in:
>
> mm/memory.c
>
> between commit:
>
> 657b5146955e ("mm: lock_vma_under_rcu() must check vma->anon_vma under vma lock")
>
> from Linus' tree and commits:
>
> 69f6bbd1317f ("mm: handle userfaults under VMA lock")
> a3bdf38e85aa ("mm: allow per-VMA locks on file-backed VMAs")
>
> from the mm tree.
>
> I fixed it up (I think, please check - see below) and can carry the fix
> as necessary. This is now fixed as far as linux-next is concerned, but
> any non trivial conflicts should be mentioned to your upstream
> maintainer when your tree is submitted for merging. You may also want
> to consider cooperating with the maintainer of the conflicting tree to
> minimise any particularly complex conflicts.
>
> --
> Cheers,
> Stephen Rothwell
>
> 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;
> +
> /* 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) {

Sorry, doesn't even build ... let me try that again.

--
Cheers,
Stephen Rothwell

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