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.

Fix LGHTM, but I am not an arm64 pgtable expert.

-- 
Thanks,

David / dhildenb


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