| 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> |
| Reviewed-by: 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); |
| _ |
