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Date: Tue, 23 Feb 2016 20:22:33 +0000
From: Will Deacon <will.deacon@arm.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>,
 Christian Borntraeger <borntraeger@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>,
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 Heiko Carstens <heiko.carstens@de.ibm.com>, linux-s390@vger.kernel.org,
 Sebastian Ott <sebott@linux.vnet.ibm.com>
Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also
 on PowerPC and ARM)
Message-ID: <20160223202233.GE27281@arm.com>
References: <20160211192223.4b517057@thinkpad>
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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...

Will