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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Larry Finger <Larry.Finger@lwfinger.net>
Cc:     Matthew Wilcox <willy@infradead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Christoph Lameter <cl@linux.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Pekka Enberg <penberg@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        ppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [Update] Regression in 4.18 - 32-bit PowerPC crashes on boot - bisected to commit 1d40a5ea01d5
In-Reply-To: <CA+55aFzZ7PND2Xvz9wB1jaCmp0rBMTSmJtKiFwSeOWy9iLSd8Q@mail.gmail.com>
References: <99169786-61dd-b19c-ac81-84bcd0a67de4@lwfinger.net> <CA+55aFzZ7PND2Xvz9wB1jaCmp0rBMTSmJtKiFwSeOWy9iLSd8Q@mail.gmail.com>
Date:   Mon, 02 Jul 2018 14:16:33 +1000
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Linus Torvalds <torvalds@linux-foundation.org> writes:
> On Fri, Jun 29, 2018 at 1:42 PM Larry Finger <Larry.Finger@lwfinger.net> wrote:
>>
>> I have more information regarding this BUG. Line 700 of page-flags.h is the
>> macro PAGE_TYPE_OPS(Table, table). For further debugging, I manually expanded
>> the macro, and found that the bug line is VM_BUG_ON_PAGE(!PageTable(page), page)
>> in routine __ClearPageTable(), which is called from pgtable_page_dtor() in
>> include/linux/mm.h. I also added a printk call to PageTable() that logs
>> page->page_type. The routine was called twice. The first had page_type of
>> 0xfffffbff, which would have been expected for a . The second call had
>> 0xffffffff, which led to the BUG.
>
> So it looks to me like the tear-down of the page tables first found a
> page that is indeed a page table, and cleared the page table bit
> (well, it set it - the bits are reversed).
...
>
> That said, can some ppc person who knows the 32-bit ppc code and maybe
> knows what that "interrupt: 700" means talk about that oddity in the
> trace, please?

I think everyone else answered your questions here, and it should be
fixed now in your tree.

Larry let me know if you're still seeing a crash with 4.18-rc3.

cheers