Re: [PATCH v4] mm/userfaultfd: detect VMA replacement after copy retry in mfill_copy_folio_retry()

Mike Rapoport
2026-04-02T04:02:51Z

On Wed, Apr 01, 2026 at 03:22:03PM -0400, Peter Xu wrote:
>
> The other thing is I just noticed the err code was changed to -EINVAL for
> snapshot changed cases, sorry I didn't follow previously as closely on the
> discussion. I think it should be -EAGAIN. It's because the userapp can't
> resolve -EINVAL failures and app will crash. In a VMA change use case, we
> should return -EAGAIN to imply the app to retry, rather than crashing.

No. The return value should express that the VMA is invalid. -EINVAL could
work, but looking now at the manual -ENOENT would be even better:

ENOENT (since Linux 4.11)
The faulting process has changed its virtual memory layout
simultaneously with an outstanding UFFDIO_COPY operation.

> Thanks,
> --
> Peter Xu

--
Sincerely yours,
Mike.