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    Subject[PATCH 5.15 32/37] mm/huge_memory: use pfn_to_online_page() in split_huge_pages_all()
    Date
    From: Naoya Horiguchi <naoya.horiguchi@nec.com>

    [ Upstream commit 2b7aa91ba0e86b8643f5d3c83874c80599c731d7 ]

    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: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") [visible after d0dc12e86b319]
    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    mm/huge_memory.c | 6 ++----
    1 file changed, 2 insertions(+), 4 deletions(-)

    diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    index 34d2979489fd..07941a1540cb 100644
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -2885,11 +2885,9 @@ 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))
    --
    2.35.1


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