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Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also
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To: Will Deacon <will.deacon@arm.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>
References: <20160211192223.4b517057@thinkpad>
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Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>, linux-s390@vger.kernel.org,
        Sebastian Ott <sebott@linux.vnet.ibm.com>
From: Christian Borntraeger <borntraeger@de.ibm.com>
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Date: Wed, 24 Feb 2016 11:16:34 +0100
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On 02/23/2016 09:22 PM, Will Deacon wrote:
> On Tue, Feb 23, 2016 at 10:33:45PM +0300, Kirill A. Shutemov wrote:
>> On Tue, Feb 23, 2016 at 07:19:07PM +0100, Gerald Schaefer wrote:
>>> I'll check with Martin, maybe it is actually trivial, then we can
>>> do a quick test it to rule that one out.
>>
>> Oh. I found a bug in __split_huge_pmd_locked(). Although, not sure if it's
>> _the_ bug.
>>
>> pmdp_invalidate() is called for the wrong address :-/
>> I guess that can be destructive on the architecture, right?
> 
> FWIW, arm64 ignores the address parameter for set_pmd_at, so this would
> only result in the TLBI nuking the wrong entries, which is going to be
> tricky to observe in practice given that we install a table entry
> immediately afterwards that maps the same pages. If s390 does more here
> (I see some magic asm using the address), that could be the answer...

This patch does not change the address for set_pmd_at, it does that for the 
pmdp_invalidate here (by keeping haddr at the start of the pmd)

--->    pmdp_invalidate(vma, haddr, pmd);
        pmd_populate(mm, pmd, pgtable);
 



Without that fix we would clearly have stale tlb entries, no?