Messages in this thread | | | Date | Wed, 16 Nov 2022 15:46:59 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH 2/2] arm64/mm: fix incorrect file_map_count for invalid pmd/pud |
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On Wed, Nov 16, 2022 at 10:08:27AM +0100, David Hildenbrand wrote: > On 16.11.22 09:38, Liu Shixin wrote: > > The page table check trigger BUG_ON() unexpectedly when split hugepage: > > > > ------------[ cut here ]------------ > > kernel BUG at mm/page_table_check.c:119! > > Internal error: Oops - BUG: 00000000f2000800 [#1] SMP > > Dumping ftrace buffer: > > (ftrace buffer empty) > > Modules linked in: > > CPU: 7 PID: 210 Comm: transhuge-stres Not tainted 6.1.0-rc3+ #748 > > Hardware name: linux,dummy-virt (DT) > > pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) > > pc : page_table_check_set.isra.0+0x398/0x468 > > lr : page_table_check_set.isra.0+0x1c0/0x468 > > [...] > > Call trace: > > page_table_check_set.isra.0+0x398/0x468 > > __page_table_check_pte_set+0x160/0x1c0 > > __split_huge_pmd_locked+0x900/0x1648 > > __split_huge_pmd+0x28c/0x3b8 > > unmap_page_range+0x428/0x858 > > unmap_single_vma+0xf4/0x1c8 > > zap_page_range+0x2b0/0x410 > > madvise_vma_behavior+0xc44/0xe78 > > do_madvise+0x280/0x698 > > __arm64_sys_madvise+0x90/0xe8 > > invoke_syscall.constprop.0+0xdc/0x1d8 > > do_el0_svc+0xf4/0x3f8 > > el0_svc+0x58/0x120 > > el0t_64_sync_handler+0xb8/0xc0 > > el0t_64_sync+0x19c/0x1a0 > > [...] > > > > On arm64, pmd_present() will return true even if the pmd is invalid. > > I assume that's because of the pmd_present_invalid() check. > > ... I wonder why that behavior was chosen. Sounds error-prone to me.
That seems to be down to commit:
b65399f6111b03df ("arm64/mm: Change THP helpers to comply with generic MM semantics")
... apparently because Andrea Arcangelli said this was necessary in:
https://lore.kernel.org/lkml/20181017020930.GN30832@redhat.com/
... but that does see to contradict what's said in:
Documentation/mm/arch_pgtable_helpers.rst
... which just says:
pmd_present Tests a valid mapped PMD
... and it's not clear to me why this *only* applies to the PMD level.
Anshuman?
Thanks, Mark.
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