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A BUG_ON is trigger in > follow_invalidate_pte as follow since this pmd is seem as pmd_trans_huge. > However this page is really a dax-pmds rather than a pmd trans huge. > > Call trace is shown as follow: > > ------------[ cut here ]------------ > kernel BUG at mm/memory.c:5185! > CPU: 0 PID: 150 Comm: kworker/u8:10 Not tainted 5.10.0-01678-g1e62aad66bbc-dirty #36 This is an old kernel, and I couldn't correlate the line number of the BUG_ON() probably because you have patches applied. But I assume this is the VM_BUG_ON() in follow_invalidate_pte()? Does this issue reproduce on more recent kernel versions (eg. v6.13)? Or some other upstream kernel version? > pc : follow_invalidate_pte+0xdc/0x5e0 > lr : follow_invalidate_pte+0xc4/0x5e0 > sp : ffffa00012997110 > Call trace: > follow_invalidate_pte+0xdc/0x5e0 > dax_entry_mkclean+0x250/0x870 > dax_writeback_one+0xac/0x380 > dax_writeback_mapping_range+0x22c/0x704 > ext4_dax_writepages+0x234/0x6e4 > do_writepages+0xc8/0x1c0 > __writeback_single_inode+0xb8/0x560 > writeback_sb_inodes+0x344/0x7a0 > wb_writeback+0x1f8/0x6b0 > wb_do_writeback+0x194/0x3cc > wb_workfn+0x14c/0x590 > process_one_work+0x470/0xa30 > worker_thread+0xac/0x510 > kthread+0x1e0/0x220 > ret_from_fork+0x10/0x18 > ---[ end trace 0f479050bd4b1818 ]--- > Kernel panic - not syncing: Oops - BUG: Fatal exception > ---[ end Kernel panic - not syncing: Oops - BUG: Fatal exception ]--- > > Commit 5c7fb56e5e3f ("mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd") and > commit 36b78402d97a ("powerpc/hash64/devmap: Use H_PAGE_THP_HUGE when > setting up huge devmap PTE entries") already check pmd_devmap during > checking pmd_trans_huge. Since pmd_devmap() is used to distinguish dax-pmds, > add the same check for arm64 to fix this problem. That seems correct to me. In practice most callers of pmd_trans_huge() that can see a dax-pmd already check for it explicitly with vma_is_dax(), but there are a few cases that don't. > Add PTE_DEVMAP in pte_modify as commit 4628a64591e6 ("mm: Preserve > _PAGE_DEVMAP across mprotect() calls") does to avoid the same issue in > mprotect. > > Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support") > Signed-off-by: Wupeng Ma > --- > arch/arm64/include/asm/pgtable.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index d3b538be1500b..b9a618127c01b 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -740,7 +740,7 @@ static inline int pmd_trans_huge(pmd_t pmd) > * as a table, so force the valid bit for the comparison. > */ > return pmd_val(pmd) && pmd_present(pmd) && > - !pmd_table(__pmd(pmd_val(pmd) | PTE_VALID)); > + !pmd_table(__pmd(pmd_val(pmd) | PTE_VALID)) && !pmd_devmap(pmd); > } > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > > @@ -1186,7 +1186,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot) > */ > const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY | > PTE_PRESENT_INVALID | PTE_VALID | PTE_WRITE | > - PTE_GP | PTE_ATTRINDX_MASK | PTE_PO_IDX_MASK; > + PTE_GP | PTE_ATTRINDX_MASK | PTE_PO_IDX_MASK | > + PTE_DEVMAP; > > /* preserve the hardware dirty information */ > if (pte_hw_dirty(pte)) > -- > 2.43.0 > >