Re: [PATCH v3] userfaultfd: reset err to be 0 when move_pages_ptes succeeded

[Suren Baghdasaryan]

On Tue, Aug 18, 2026 at 8:27 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, 19 Aug 2026 10:08:24 +0700 (WIB) Foxie Flakey <foxieflakey@xxxxxxxxx> wrote:
>
> >
> > During move_pages() operation, when move_pages_ptes() returns EAGAIN,
> > the error code is not cleared even after we processed it. This leads
> > to a successful retry but then the same pages are retried again due to
> > the stale error code. This time move fails because pages are already
> > moved, loop is terminated and move_pages() reports a failure.
> > Clear the error code once we processes EAGAIN.
> >
> > Fixes: 50944692052b ("userfaultfd: opportunistic TLB-flush batching for present pages in MOVE")
> > Assisted-by: ChatGPT:GPT-5.6-Luna
> > Signed-off-by: Bryan Lim <foxieflakey@xxxxxxxxx>

Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>

>
> Thanks, Bryan.
>
> More paperwork: the signoff is supposed to match the Author:.  The way
> to do this is to add an explicit From: line at start-of-changelog.  If
> this is not present, we fall back to the email envelope's From:.
>
> > --- a/mm/userfaultfd.c
> > +++ b/mm/userfaultfd.c
> > @@ -2085,8 +2085,10 @@ static ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
> >               }
> >
> >               if (err) {
> > -                     if (err == -EAGAIN)
> > +                     if (err == -EAGAIN) {
> > +                             err = 0;
> >                               continue;
> > +                     }
> >                       break;
> >               }
>
> I'll queue it, with an adjusted From:, as above.
>
> Could reviewers please advise on whether we should backport this into
> -stable kernels?

Yes please. The first version where the bug appears is 6.18.
Thanks!

>
>