Re: [PATCH V14] mm/debug: Add tests validating architecture page table helpers

[Christophe Leroy]

Le 04/03/2020 Ã 02:39, Qian Cai a ÃcritÂ:
> > Below is slightly modified version of your change above and should still
> > prevent the bug on powerpc. Will it be possible for you to re-test this
> > ? Once confirmed, will send a patch enabling this test on powerpc64
> > keeping your authorship. Thank you.
>
> This works fine on radix MMU but I decided to go a bit future to test hash
> MMU. The kernel will stuck here below. I did confirm that pte_alloc_map_lock()
> was successful, so I donât understand hash MMU well enough to tell why
> it could still take an interrupt at pte_clear_tests() even before we calls
> pte_unmap_unlock()?

AFAIU, you are not taking an interrupt here. You are stuck in the 
pte_update(), most likely due to nested locks. Try with LOCKDEP ?

Christophe

> [   33.881515][    T1] ok 8 - property-entry
> [   33.883653][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
> architecture page table helpers
> [   60.418885][    C8] watchdog: BUG: soft lockup - CPU#8 stuck for 23s!
> [swapper/0:1]