Re: [PATCH] m68k: fix "bad page state" oops on ColdFire boot

[Greg Ungerer]

Hi Geert,

On 18/06/18 16:58, Geert Uytterhoeven wrote:
> Hi Greg,
>
> On Mon, Jun 18, 2018 at 8:06 AM Greg Ungerer <gerg@xxxxxxxxxxxxxx> wrote:
> > Booting a ColdFire m68k core with MMU enabled causes a "bad page state"
> > oops since commit 1d40a5ea01d5 ("mm: mark pages in use for page tables"):
> >
> >   BUG: Bad page state in process sh  pfn:01ce2
> >   page:004fefc8 count:0 mapcount:-1024 mapping:00000000 index:0x0
> >   flags: 0x0()
> >   raw: 00000000 00000000 00000000 fffffbff 00000000 00000100 00000200 00000000
> >   raw: 039c4000
> >   page dumped because: nonzero mapcount
> >   Modules linked in:
> >   CPU: 0 PID: 22 Comm: sh Not tainted 4.17.0-07461-g1d40a5ea01d5 #13
> >
> > Fix by calling pgtable_page_dtor() in our __pte_free_tlb() code path,
> > so that the PG_table flag is cleared before we free the pte page.
> >
> > Signed-off-by: Greg Ungerer <gerg@xxxxxxxxxxxxxx>
> > CC: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
> > ---
> >   arch/m68k/include/asm/mcf_pgalloc.h | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > Matthew: I came across this thread at https://lkml.org/lkml/2018/6/17/163
> >           about a similar problem with openrisc. Based on that I came up
> >           with this fix for m68k/ColdFire. Fixes the issue for me.
> >
> > diff --git a/arch/m68k/include/asm/mcf_pgalloc.h b/arch/m68k/include/asm/mcf_pgalloc.h
> > index 8b707c249026..8c441eb57b80 100644
> > --- a/arch/m68k/include/asm/mcf_pgalloc.h
> > +++ b/arch/m68k/include/asm/mcf_pgalloc.h
> > @@ -44,6 +44,7 @@ extern inline pmd_t *pmd_alloc_kernel(pgd_t *pgd, unsigned long address)
> >   static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t page,
> >                                    unsigned long address)
> >   {
> > +       pgtable_page_dtor(page);
> >          __free_page(page);
> >   }
>
> Do you need a call to pgtable_page_dtor() in pte_free(), too?
> On x86 (and motorola_pgalloc.h and sun3_pgalloc.h FWIW), both functions
> call pgtable_page_dtor().

I am thinking yes, looking at those other examples.

Regards
Greg