Re: [PATCH] mm: don't allow empty relative nodemask in mpol_relative_nodemask()

[Yury Norov]

On Thu, May 28, 2026 at 03:37:04PM -0400, Waiman Long wrote:
> On 5/28/26 3:03 PM, Yury Norov wrote:
> > Reassigning nodes relative an empty user-provided nodemask is useless,
> > and triggers divide-by-zero in the function.
> > 
> > Reported-by: Farhad Alemi <farhad.alemi@xxxxxxxxxxxx>
> > Link: https://lore.kernel.org/all/CA+0ovCgxbZkXa+OU8w3s84R3KNPNxxRfmsNR-udh+afQBbGNmw@xxxxxxxxxxxxxx/
> > Signed-off-by: Yury Norov <ynorov@xxxxxxxxxx>
> > ---
> >   mm/mempolicy.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 4e4421b22b59..cd961fa1eb33 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -370,8 +370,13 @@ static inline int mpol_store_user_nodemask(const struct mempolicy *pol)
> >   static void mpol_relative_nodemask(nodemask_t *ret, const nodemask_t *orig,
> >   				   const nodemask_t *rel)
> >   {
> > +	unsigned int w = nodes_weight(*rel);
> >   	nodemask_t tmp;
> > -	nodes_fold(tmp, *orig, nodes_weight(*rel));
> > +
> > +	if (w == 0)
> > +		return -EINVAL;
> > +
> > +	nodes_fold(tmp, *orig, w);
> >   	nodes_onto(*ret, tmp, *rel);
> >   }
> 
> mpol_relative_nodemask() is a void function, so this code should fail
> compilation. Right?

Apologize, submitted the wrong file. Will resend shortly.