Re: [PATCH -next 5/7] mm: memory: convert wp_page_copy() to use folios

[Kefeng Wang]

On 2023/1/14 6:16, SeongJae Park wrote:
> Hello,
>
> On Fri, 13 Jan 2023 19:04:14 +0000 Lorenzo Stoakes <lstoakes@xxxxxxxxx> wrote:
>
> > On Fri, Jan 13, 2023 at 02:08:36PM +0100, David Hildenbrand wrote:
> > > On 13.01.23 14:01, Marek Szyprowski wrote:
> > > > Hi
> > > >
> > > > On 12.01.2023 09:30, Kefeng Wang wrote:
> > > > > The old_page/new_page are converted to old_folio/new_folio in
> > > > > wp_page_copy(), then replaced related page functions to folio
> > > > > functions.
> > > > >
> > > > > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > > >
> > > > This patch, merged into today's linux-next as commit 9ebae00c8e30 ("mm:
> > > > memory: convert wp_page_copy() to use folios"), causes serious stability
> > > > issues on my ARM based test boards. Here is the example of such crash:
> > >
> > > syzbot is also not happy:
> > >
> > > https://lkml.kernel.org/r/000000000000807c7805f2205df1@xxxxxxxxxx
> > >
> > > --
> > > Thanks,
> > >
> > > David / dhildenb
> >
> > This also completely broke my qemu environment.
>
> Same to me.
>
> > In that thread Willy points out that the issue stems from blindly assigning
> > page_folio(old_page) to old_folio without checking whether it is NULL first,
> > therefore triggering a NULL pointer deref.
> >
> > A quick fix would be to put in a check (as shown below) which fixes the issue,
> > but as Willy said, I think we should drop this until it can be fixed in a
> > respin.

Hello all, sorry for the break, thanks all to quick fix and analysis, as 
the patch has be dropped from mm-unstable and next, will resend after 
address some comments from Matthew Wilcox and do more test.