Re: [PATCH] mm/page_isolation: fix potential missing call to unset_migratetype_isolate()

[David Hildenbrand]

On 06.09.21 11:38, Miaohe Lin wrote:
> On 2021/9/6 17:27, David Hildenbrand wrote:
> > On 04.09.21 11:20, Miaohe Lin wrote:
> > > In start_isolate_page_range() undo path, pfn_to_online_page() just checks
> > > the first pfn in a pageblock while __first_valid_page() will traverse the
> > > pageblock until the first online pfn is found. So we may miss the call to
> > > unset_migratetype_isolate() in undo path and pages will remain isolated
> > > unexpectedly. Fix this by calling undo_isolate_page_range() and this will
> > > also help to remove some duplicated codes.
> > >
> > > Fixes: 2ce13640b3f4 ("mm: __first_valid_page skip over offline pages")
> >
> > While that is true, we shouldn't ever trigger, neither via cma, virtio-mem nor memory offlining, because essentially all operate on MAX_ORDER -1 -aligned ranges without memory holes.
>
> I think this should never trigger too. It's a theoretical issue. So is the Fixes tag necessary ?

I think it's one of these "let's add Fixes: but no need for Cc: stable".

BUT in older kernels we could have triggered this via memory offlining 
eventually ... before c5e79ef561b0 ("mm/memory_hotplug.c: don't allow to 
online/offline memory blocks with holes") ... so maybe even a Cc: stable?

--
Thanks,

David / dhildenb