Hi Greg!
Thanks a lot for quickly looking into this and sharing your notes here.
On Wed, Nov 22, 2023 at 5:53 PM Gregory Price
<gregory.price@xxxxxxxxxxxx> wrote:
>
> > Please note the initial `maxnode` parameter from `mbind` was omitted
> > to ensure the API doesn't exceed 6 arguments. Instead, the constant
> > MAX_NUMNODES was utilized.
> >
>
> I don't think this will work, users have traditionally been allowed to
> shorten their nodemasks, and also for some level of portability.
>
> We may want to consider an arg structure, rather than just chopping an
> argument off.
>
Yes, good point... that should be considered as a more complete
long-term approach beyond the MVP.
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 10a590ee1c89..91ee300fa728 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -1215,11 +1215,10 @@ static struct folio *alloc_migration_target_by_mpol(struct folio *src,
> > }
> > #endif
> >
> > -static long do_mbind(unsigned long start, unsigned long len,
> > +static long do_mbind(struct mm_struct *mm, unsigned long start, unsigned long len,
> > unsigned short mode, unsigned short mode_flags,
> > nodemask_t *nmask, unsigned long flags)
> > {
> > - struct mm_struct *mm = current->mm;
> > struct vm_area_struct *vma, *prev;
> > struct vma_iterator vmi;
> > struct migration_mpol mmpol;
> > @@ -1465,10 +1464,84 @@ static inline int sanitize_mpol_flags(int *mode, unsigned short *flags)
> > return 0;
> > }
>
> This is a completely insufficient change to do_mbind. do_mbind utilizes
> `current` in a variety of places for nodemask (cpuset) validation and to
> acquire the task's lock. This will not work the way you intend it to,
> you end up mixing up node masks between current and target task.
>
Oh oh. True! Good catch!
> see here:
> https://lore.kernel.org/all/20231122211200.31620-7-gregory.price@xxxxxxxxxxxx/
>
Let me go over this... Thanks!
> We may want to combine this change and with my change so that your iovec
> changes can be re-used, because that is a very nice feature.
>
Sounds good. Thanks again!
Best,
Vinicius
