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 02:39:02PM +0200, David Hildenbrand wrote:
> On 07.09.22 14:11, Naoya Horiguchi wrote:
...
> > ---
> >  From 8a5c284df732943065d23838090d15c94cd10395 Mon Sep 17 00:00:00 2001
> > From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > Date: Wed, 7 Sep 2022 20:58:44 +0900
> > Subject: [PATCH] mm/huge_memory: use pfn_to_online_page() in
> >   split_huge_pages_all()
> > 
> > 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")
> > Suggested-by: David Hildenbrand <david@redhat.com>
> 
> Feel free to use
> 
> Co-developed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Sure, I'll add these.

> instead
> 
> > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > Cc: <stable@vger.kernel.org>
> > ---
> >   mm/huge_memory.c | 7 ++-----
> >   1 file changed, 2 insertions(+), 5 deletions(-)
> > 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 5fa2ba86dae4..03149a8f46f9 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -2894,11 +2894,8 @@ static void split_huge_pages_all(void)
> >   		max_zone_pfn = zone_end_pfn(zone);
> >   		for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
> >   			int nr_pages;
> 
> Add an empty line here please, while at it.

Added it.

> > -			if (!pfn_valid(pfn))
> > -				continue;
> > -
> > -			page = pfn_to_page(pfn);
> > -			if (!get_page_unless_zero(page))
> > +			page = pfn_to_online_page(pfn);
> > +			if (!page || !get_page_unless_zero(page))
> >   				continue;
> >   			if (zone != page_zone(page))
> 
> Can you send the patch "officially" as well? Thanks

Yes, I'll send this later in the normal patch submission manner.

Thanks,
Naoya Horiguchi