The patch titled Subject: mm: sparsemem: fix missing higher order allocation splitting has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-sparsemem-fix-missing-higher-order-allocation-splitting.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: Muchun Song songmuchun@bytedance.com Subject: mm: sparsemem: fix missing higher order allocation splitting Date: Mon, 20 Jun 2022 10:30:19 +0800

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.

Link: https://lkml.kernel.org/r/20220620023019.94257-1-songmuchun@bytedance.com Fixes: d8d55f5616cf ("mm: sparsemem: use page table lock to protect kernel pmd operations") Signed-off-by: Muchun Song songmuchun@bytedance.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Xiongchun Duan duanxiongchun@bytedance.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/sparse-vmemmap.c | 8 ++++++++ 1 file changed, 8 insertions(+)

--- a/mm/sparse-vmemmap.c~mm-sparsemem-fix-missing-higher-order-allocation-splitting +++ a/mm/sparse-vmemmap.c @@ -78,6 +78,14 @@ static int __split_vmemmap_huge_pmd(pmd_

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); _

Patches currently in -mm which might be from songmuchun@bytedance.com are

mm-sparsemem-fix-missing-higher-order-allocation-splitting.patch mm-memory_hotplug-enumerate-all-supported-section-flags.patch mm-memory_hotplug-enumerate-all-supported-section-flags-v5.patch mm-memory_hotplug-make-hugetlb_optimize_vmemmap-compatible-with-memmap_on_memory.patch mm-memory_hotplug-make-hugetlb_optimize_vmemmap-compatible-with-memmap_on_memory-v5.patch mm-hugetlb-remove-minimum_order-variable.patch mm-memcontrol-remove-dead-code-and-comments.patch mm-rename-unlock_page_lruvec_irq-_irqrestore-to-lruvec_unlock_irq-_irqrestore.patch mm-memcontrol-prepare-objcg-api-for-non-kmem-usage.patch mm-memcontrol-make-lruvec-lock-safe-when-lru-pages-are-reparented.patch mm-vmscan-rework-move_pages_to_lru.patch mm-thp-make-split-queue-lock-safe-when-lru-pages-are-reparented.patch mm-memcontrol-make-all-the-callers-of-foliopage_memcg-safe.patch mm-memcontrol-introduce-memcg_reparent_ops.patch mm-memcontrol-use-obj_cgroup-apis-to-charge-the-lru-pages.patch mm-lru-add-vm_warn_on_once_folio-to-lru-maintenance-function.patch mm-lru-use-lruvec-lock-to-serialize-memcg-changes.patch