On Mon, 3 Apr 2017, Michal Hocko wrote:
> On Fri 31-03-17 20:58:16, Ben Hutchings wrote:
> > On Tue, 2017-03-28 at 15:11 +0200, Michal Hocko wrote:
> > > On Wed 22-03-17 10:09:43, Jiri Slaby wrote:
> > > [...]
> > > > @@ -1245,6 +1254,10 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
> > > >
> > > > page = pmd_page(*pmd);
> > > > VM_BUG_ON(!PageHead(page));
> > > > +
> > > > + if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, page, flags))
> > > > + goto out;
> > > > +
> > > > if (flags & FOLL_TOUCH) {
> > > > pmd_t _pmd;
> > > > /*
> > >
> > > I have just noticed that this patch is not correct fo 3.12 because we
> > > should return NULL rather than the page in this case. 3.2 is wrong as
> > > well AFAICS.
> >
> > Thanks for reporting this. This is the same mistake I made initially
> > with follow_page() in 3.2. But I had a test case which caught that
> > before release, and I don't have a test case for this.
>
> I believe Miroslav has used the test case embeded in the patch
> description to catch the bug.
That is correct.
Miroslav