On Fri, May 01, 2020 at 01:41:58AM +0530, Souptick Joarder wrote: > As per documentation, pin_user_pages_fast() & get_user_pages_fast() > will return 0, if nr_pages <= 0. But this can be figure out only after > going inside the internal_get_user_pages_fast(). Why is nr_pages not unsigned? I seem to have convinced myself before that there was a good reason for it but really what is the point of calling either of these functions with nr_pages not > 0? > > This can be handled early. Adding a check for the same. > > Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx> > --- > mm/gup.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/gup.c b/mm/gup.c > index 50681f0..a13aaa6 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2817,6 +2817,8 @@ int get_user_pages_fast(unsigned long start, int nr_pages, > */ > if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > return -EINVAL; > + if (nr_pages <= 0) > + return 0; I think the documentation may be wrong here... Is there a caller who expects a return of 0 for this behavior? It seems like these should be a warn on and return -EINVAL. I just don't see the use case here. Ira > > /* > * The caller may or may not have explicitly set FOLL_GET; either way is > @@ -2854,6 +2856,8 @@ int pin_user_pages_fast(unsigned long start, int nr_pages, > /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > return -EINVAL; > + if (nr_pages <= 0) > + return 0; > > gup_flags |= FOLL_PIN; > return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); > -- > 1.9.1 > >
