The patch titled Subject: mm/huge_memory: use pfn_to_online_page() in split_huge_pages_all() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-huge_memory-use-pfn_to_online_page-in-split_huge_pages_all.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Naoya Horiguchi naoya.horiguchi@nec.com Subject: mm/huge_memory: use pfn_to_online_page() in split_huge_pages_all() Date: Thu, 8 Sep 2022 13:11:50 +0900

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.

Link: https://lkml.kernel.org/r/20220908041150.3430269-1-naoya.horiguchi@linux.dev Fixes: 49071d436b51 ("thp: add debugfs handle to split all huge pages") Signed-off-by: Naoya Horiguchi naoya.horiguchi@nec.com Co-developed-by: David Hildenbrand david@redhat.com Signed-off-by: David Hildenbrand david@redhat.com Reviewed-by: Yang Shi shy828301@gmail.com Acked-by: Michal Hocko mhocko@suse.com Reviewed-by: Miaohe Lin linmiaohe@huawei.com Reviewed-by: Oscar Salvador osalvador@suse.de Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Matthew Wilcox willy@infradead.org Cc: Muchun Song songmuchun@bytedance.com Cc: stable@vger.kernel.org [5.10+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/huge_memory.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-use-pfn_to_online_page-in-split_huge_pages_all +++ a/mm/huge_memory.c @@ -2894,11 +2894,9 @@ 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; - 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)) _

Patches currently in -mm which might be from naoya.horiguchi@nec.com are

mm-huge_memory-use-pfn_to_online_page-in-split_huge_pages_all.patch