Re: [PATCH v23 12/28] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW

Kirill A. Shutemov
2021-03-22T11:39:43Z

On Mon, Mar 22, 2021 at 11:46:21AM +0100, Peter Zijlstra wrote:
> On Mon, Mar 22, 2021 at 01:15:02PM +0300, Kirill A. Shutemov wrote:
> > On Tue, Mar 16, 2021 at 08:10:38AM -0700, Yu-cheng Yu wrote:
>
> > > + pte_t old_pte, new_pte;
> > > +
> > > + old_pte = READ_ONCE(*ptep);
> > > + do {
> > > + new_pte = pte_wrprotect(old_pte);
> > > + } while (!try_cmpxchg(&ptep->pte, &old_pte.pte, new_pte.pte));
> >
> > I think this is wrong. You need to update old_pte on every loop iteration,
> > otherwise you can get in to endless loop.
>
> It is correct, please consider why the old argument is a pointer.

Ah, right. Sorry for the noise.

--
Kirill A. Shutemov