Messages in this thread | | | Date | Thu, 17 Nov 2022 09:39:48 +0530 | Subject | Re: [PATCH 1/2] arm64/mm: fix incorrect file_map_count for non-leaf pmd/pud | From | Anshuman Khandual <> |
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On 11/16/22 14:08, Liu Shixin wrote: > The page table check trigger BUG_ON() unexpectedly when collapse hugepage: > > ------------[ cut here ]------------ > kernel BUG at mm/page_table_check.c:82! > Internal error: Oops - BUG: 00000000f2000800 [#1] SMP > Dumping ftrace buffer: > (ftrace buffer empty) > Modules linked in: > CPU: 6 PID: 68 Comm: khugepaged Not tainted 6.1.0-rc3+ #750 > Hardware name: linux,dummy-virt (DT) > pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) > pc : page_table_check_clear.isra.0+0x258/0x3f0 > lr : page_table_check_clear.isra.0+0x240/0x3f0 > [...] > Call trace: > page_table_check_clear.isra.0+0x258/0x3f0 > __page_table_check_pmd_clear+0xbc/0x108 > pmdp_collapse_flush+0xb0/0x160 > collapse_huge_page+0xa08/0x1080 > hpage_collapse_scan_pmd+0xf30/0x1590 > khugepaged_scan_mm_slot.constprop.0+0x52c/0xac8 > khugepaged+0x338/0x518 > kthread+0x278/0x2f8 > ret_from_fork+0x10/0x20 > [...] > > Since pmd_user_accessible_page() doesn't check if a pmd is leaf, it > decrease file_map_count for a non-leaf pmd comes from collapse_huge_page(). > and so trigger BUG_ON() unexpectedly.
Could you please provide the pmd_val() on the pmd entry, that triggers this BUG_ON() here ? Only additional thing pmd_leaf() ensures, is that the entry is not a table one.
#define pmd_leaf(pmd) (pmd_present(pmd) && !pmd_table(pmd))
collapse_huge_page() pmd is non-leaf because it has table bit on ?
> > Fix this problem by using pmd_leaf() insteal of pmd_present() in > pmd_user_accessible_page(). Moreover, use pud_leaf() for > pud_user_accessible_page() too. > > Fixes: 42b2547137f5 ("arm64/mm: enable ARCH_SUPPORTS_PAGE_TABLE_CHECK") > Reported-by: Denys Vlasenko <dvlasenk@redhat.com> > Signed-off-by: Liu Shixin <liushixin2@huawei.com> > --- > arch/arm64/include/asm/pgtable.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 71a1af42f0e8..edf6625ce965 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -863,12 +863,12 @@ static inline bool pte_user_accessible_page(pte_t pte) > > static inline bool pmd_user_accessible_page(pmd_t pmd) > { > - return pmd_present(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)); > + return pmd_leaf(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)); > } > > static inline bool pud_user_accessible_page(pud_t pud) > { > - return pud_present(pud) && pud_user(pud); > + return pud_leaf(pud) && pud_user(pud); > } > #endif >
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