Re: [PATCH] mm/huge_memory: use pfn_to_online_page() in split_huge_pages_all()

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Wed, Sep 07, 2022 at 01:57:45PM -0700, Andrew Morton wrote:
> On Wed, 7 Sep 2022 21:11:57 +0900 Naoya Horiguchi <naoya.horiguchi@linux.dev> wrote:
> 
> > 
> > NULL pointer dereference is triggered when calling thp split via debugfs
> > on the system with offlined memory blocks.  With debug option enabled,
> > the following kernel messages are printed out:
> > 
> >   page:00000000467f4890 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x121c000
> >   flags: 0x17fffc00000000(node=0|zone=2|lastcpupid=0x1ffff)
> >   raw: 0017fffc00000000 0000000000000000 dead000000000122 0000000000000000
> >   raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
> >   page dumped because: unmovable page
> >   page:000000007d7ab72e is uninitialized and poisoned
> >   page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> >   ------------[ cut here ]------------
> >   kernel BUG at include/linux/mm.h:1248!
> >   invalid opcode: 0000 [#1] PREEMPT SMP PTI
> >   CPU: 16 PID: 20964 Comm: bash Tainted: G          I        6.0.0-rc3-foll-numa+ #41
> >   ...
> >   RIP: 0010:split_huge_pages_write+0xcf4/0xe30
> > 
> > This shows that page_to_nid() in page_zone() is unexpectedly called for an
> > offlined memmap.
> > 
> > Use pfn_to_online_page() to get struct page in PFN walker.
> > 
> > Fixes: 49071d436b51 ("thp: add debugfs handle to split all huge pages")
> 
> January of 2016!  Or was this a long-term bug which was recently
> exposed by some other change?

Maybe yes, I confirmed that this issue reproduces in kernel 5.10 (released
on Dec 13, 2020, which might not be so "recent"), but does not reproduce in
kernel 5.4.  So I think that marking "5.10+" for stable is fine.

Thanks,
Naoya Horiguchi