Re: [PATCH 1/2] mm/hmm: hmm_range_fault() NULL pointer bug

[Ralph Campbell]

On 8/26/19 11:09 AM, Jason Gunthorpe wrote:
> On Mon, Aug 26, 2019 at 11:02:12AM -0700, Ralph Campbell wrote:
> > On 8/24/19 3:37 PM, Christoph Hellwig wrote:
> > > On Fri, Aug 23, 2019 at 03:17:52PM -0700, Ralph Campbell wrote:
> > > > Although hmm_range_fault() calls find_vma() to make sure that a vma exists
> > > > before calling walk_page_range(), hmm_vma_walk_hole() can still be called
> > > > with walk->vma == NULL if the start and end address are not contained
> > > > within the vma range.
> > >
> > > Should we convert to walk_vma_range instead?  Or keep walk_page_range
> > > but drop searching the vma ourselves?
> > >
> > > Except for that the patch looks good to me:
> > >
> > > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> >
> > I think keeping the call to walk_page_range() makes sense.
> > Jason is hoping to be able to snapshot a range with & without vmas
> > and have the pfns[] filled with empty/valid entries as appropriate.
> >
> > I plan to repost my patch changing hmm_range_fault() to use
> > walk.test_walk which will remove the call to find_vma().
> > Jason had some concerns about testing it so that's why I have
> > been working on some HMM self tests before resending it.
>
> I'm really excited to see tests for hmm_range_fault()!
>
> Did you find this bug with the tests??
>
> Jason

Yes, I found both bugs with the tests.
I started with Jerome's hmm_dummy driver and user level test code.
Hopefully I can send it out this week.