Re: [PATCH] mm/gup.c: Fix return value for __gup_longterm_locked()

[Shigeru Yoshida <syoshida@redhat.com>]

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On Mon, Aug 22, 2022 at 9:14 AM John Hubbard <jhubbard@nvidia.com> wrote:

> On 8/21/22 11:35, Shigeru Yoshida wrote:
> > __get_user_pages_locked() may return the number of pages less than
> > nr_pages.  So __gup_longterm_locked() have to return the number of
> > pages __get_user_pages_locked() returns if it succeeded, not nr_pages
> > passed.
>
> s/passed/requested/
>
> >
> > Fixes: 61c63c2076d9 (mm/gup.c: simplify and fix
> check_and_migrate_movable_pages() return codes)
> > CC: Alistair Popple <apopple@nvidia.com>
> > Reported-by: syzbot+616ff0452fec30f4dcfd@syzkaller.appspotmail.com
> > Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
> > ---
> >   mm/gup.c | 12 ++++++------
> >   1 file changed, 6 insertions(+), 6 deletions(-)
>
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
>

Hi John,

Thank you so much for your review.
I'll send v2 patch.

Shigeru


>
> (with a couple of nits about line length, below)
>
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 5aa7531a703b..542cf74c59b0 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -2068,22 +2068,22 @@ static long __gup_longterm_locked(struct
> mm_struct *mm,
> >                                 unsigned int gup_flags)
> >   {
> >       unsigned int flags;
> > -     long rc;
> > +     long rc, nr_pinned_pages;
> >
> >       if (!(gup_flags & FOLL_LONGTERM))
> >               return __get_user_pages_locked(mm, start, nr_pages, pages,
> vmas,
> >                                              NULL, gup_flags);
> >       flags = memalloc_pin_save();
> >       do {
> > -             rc = __get_user_pages_locked(mm, start, nr_pages, pages,
> vmas,
> > -                                          NULL, gup_flags);
> > -             if (rc <= 0)
> > +             nr_pinned_pages = __get_user_pages_locked(mm, start,
> nr_pages, pages, vmas,
> > +                                                       NULL, gup_flags);
>
> Can you please wrap at 80 cols, though?
>
> > +             if (nr_pinned_pages <= 0)
> >                       break;
> > -             rc = check_and_migrate_movable_pages(rc, pages, gup_flags);
> > +             rc = check_and_migrate_movable_pages(nr_pinned_pages,
> pages, gup_flags);
>
> Also here.
>
> >       } while (rc == -EAGAIN);
> >       memalloc_pin_restore(flags);
> >
> > -     return rc ? rc : nr_pages;
> > +     return rc ? rc : nr_pinned_pages;
> >   }
> >
> >   static bool is_valid_gup_flags(unsigned int gup_flags)
>
> thanks,
> --
> John Hubbard
> NVIDIA
>
>

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