+ mm-sparsemem-fix-missing-higher-order-allocation-splitting.patch added to mm-hotfixes-unstable branch

+ mm-sparsemem-fix-missing-higher-order-allocation-splitting.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

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/mm-sparsemem-fix-missing-higher-order-allocation-splitting.patch

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