Re: [PATCH 2/2] mm/khugepaged: Fix a NULL vs IS_ERR() bug in collapse_pte_mapped_thp()

[Dan Carpenter <dan.carpenter@linaro.org>]

On Mon, Oct 23, 2023 at 07:59:12AM +0300, Dan Carpenter wrote:
> On Fri, Oct 20, 2023 at 09:49:15AM -0700, Vishal Moola wrote:
> > On Fri, Oct 20, 2023 at 9:36 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> > >
> > > On Fri, 20 Oct 2023 17:14:36 +0300 Dan Carpenter <dan.carpenter@linaro.org> wrote:
> > >
> > > > This was changed from find_lock_page() which returns NULL to
> > > > filemap_lock_folio() which returns error pointers.  Update the
> > > > error checking to match.
> > > >
> > > > --- a/mm/khugepaged.c
> > > > +++ b/mm/khugepaged.c
> > > > @@ -1508,7 +1508,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> > > >
> > > >       folio = filemap_lock_folio(vma->vm_file->f_mapping,
> > > >                              linear_page_index(vma, haddr));
> > > > -     if (!folio)
> > > > +     if (IS_ERR(folio))
> > > >               return SCAN_PAGE_NULL;
> > > >
> > > >       if (folio_order(folio) != HPAGE_PMD_ORDER) {
> > >
> > > Also doesn't appear applicable to current kernels?
> > 
> > Thanks for these. Both these fix patches address issues introduced by my
> > khugepaged folio conversion patchset:
> > https://lore.kernel.org/linux-mm/20231018203213.50224-1-vishal.moola@gmail.com/T/#t
> > 
> > Andrew already dropped the patchset from current kernels so I can fix a
> > couple issues, v3 will include all these fixes.
> 
> 
> Only this one was introduced by your patchset.  The other bug is older.
> I don't know why it only showed up as a new bug now.  I had guessed that
> it was other changes I had made to Smatch which affected this.

Heh.  Nope.  I was wrong.  These were both introduces as part of the
folio conversion patchset.

Thanks for taking care of this, Vishal.

regards,
dan carpenter