On 06/20/22 10:30, Muchun Song wrote:
> Higher order allocations for vmemmap pages from buddy allocator must be
> able to be treated as indepdenent small pages as they can be freed
> individually by the caller. There is no problem for higher order vmemmap
> pages allocated at boot time since each individual small page will be
> initialized at boot time. However, it will be an issue for memory hotplug
> case since those higher order vmemmap pages are allocated from buddy
> allocator without initializing each individual small page's refcount. The
> system will panic in put_page_testzero() when CONFIG_DEBUG_VM is enabled
> if the vmemmap page is freed.
>
> Fixes: d8d55f5616cf ("mm: sparsemem: use page table lock to protect kernel pmd operations")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
> mm/sparse-vmemmap.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
Thanks for fixing,
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
--
Mike Kravetz
>
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 652f11a05749..ebb489fcf07c 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -78,6 +78,14 @@ static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
>
> spin_lock(&init_mm.page_table_lock);
> if (likely(pmd_leaf(*pmd))) {
> + /*
> + * Higher order allocations from buddy allocator must be able to
> + * be treated as indepdenent small pages (as they can be freed
> + * individually).
> + */
> + if (!PageReserved(page))
> + split_page(page, get_order(PMD_SIZE));
> +
> /* Make pte visible before pmd. See comment in pmd_install(). */
> smp_wmb();
> pmd_populate_kernel(&init_mm, pmd, pgtable);
> --
> 2.11.0
>
