Re: [BUG] mm/hugetlb: possible temporary resv underflow

[Guillaume Morin <guillaume@morinfr.org>]

On 14 Jul  4:14, Breno Leitao wrote:
>
> On Tue, Jul 14, 2026 at 12:48:16PM +0200, Guillaume Morin wrote:
> > > > I am not sure what the best fix is but checking folio_mapcount() == 0 
> > > > in __unmap_hugepage_range() seems to do the trick
> > > > 
> > > >                 adjust_reservation = false;
> > > >  
> > > >                 spin_lock_irq(&hugetlb_lock);
> > > >                 if (!h->surplus_huge_pages && __vma_private_lock(vma) &&
> > > > -                   folio_test_anon(folio)) {
> > > > +                   folio_test_anon(folio) &&
> > > > +                   folio_mapcount(folio) == 0) {
> > > >                         folio_set_hugetlb_restore_reserve(page_folio(page));
> > > >                         /* Reservation to be adjusted after the spin lock */
> > > >                         adjust_reservation = true;
> > > 
> > > The fix looks correct to me.
> > 
> > Excellent! Will you be submitting a patch or do you need me to do
> > something there?
> 
> Up to you. You can either send it, or, I  can do it myself.

I just sent a patch, hopefully it does the job.

Did you have the chance of looking at the selftest version of the repro?
Should I spin up a patch for this as well?

Guillaume.

-- 
Guillaume Morin <guillaume@morinfr.org>