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Subject: Re: [PATCH] m68k: fix "bad page state" oops on ColdFire boot
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Matthew Wilcox <mawilcox@microsoft.com>,
        Linux/m68k <linux-m68k@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <20180618060426.24497-1-gerg@linux-m68k.org>
 <CAMuHMdXSaGtremvLCRzKm68s_dUEigL-VCmM-ar=T4PPJrECLw@mail.gmail.com>
From:   Greg Ungerer <gerg@linux-m68k.org>
Message-ID: <8cd9643d-0855-ac30-41cb-7de24314da00@linux-m68k.org>
Date:   Mon, 18 Jun 2018 23:59:40 +1000
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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@linux-m68k.org> 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@linux-m68k.org>
>> CC: Matthew Wilcox <mawilcox@microsoft.com>
>> ---
>>   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