Re: [PATCH 1/2] arm64/mm: fix incorrect file_map_count for non-leaf pmd/pud
From: Anshuman Khandual <hidden>
Date: 2022-11-17 04:10:03
Also in:
lkml
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 ?
quoted hunk ↗ jump to hunk
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 <redacted> Signed-off-by: Liu Shixin <redacted> --- 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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