On Thu, Aug 04, 2022 at 03:40:50PM -0700, Andrew Morton wrote:
> On Wed, 3 Aug 2022 18:03:29 -0400 Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> > These bits should only be valid when the ptes are present. Introducing two
> > booleans for it and set it to false when !pte_present().
>
> Please (always) describe the user visible runtime effects of the bug
> which is being fixed?
Will do in the future.
For this specific one I'll add some more details:
The bug is found during code reading and no real world issue reported,
but logically such an error can cause incorrect readings for either smaps
or smaps_rollup output on quite a few fields.
For example, it could cause over-estimate on values like Shared_Dirty,
Private_Dirty, Referenced; or it could also cause under-estimate on
values like LazyFree, Shared_Clean, Private_Clean.
Meanwhile I think I overlooked the pmd handling which seems to have the
same issue but done in another commit.. Will repost soon.
Thanks,
>
>
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> > struct vm_area_struct *vma = walk->vma;
> > bool locked = !!(vma->vm_flags & VM_LOCKED);
> > struct page *page = NULL;
> > - bool migration = false;
> > + bool migration = false, young = false, dirty = false;
> >
> > if (pte_present(*pte)) {
> > page = vm_normal_page(vma, addr, *pte);
> > + young = pte_young(*pte);
> > + dirty = pte_dirty(*pte);
> > } else if (is_swap_pte(*pte)) {
> > swp_entry_t swpent = pte_to_swp_entry(*pte);
> >
> > @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> > if (!page)
> > return;
> >
> > - smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> > - locked, migration);
> > + smaps_account(mss, page, false, young, dirty, locked, migration);
> > }
> >
> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > --
> > 2.32.0
>
--
Peter Xu
