From mboxrd@z Thu Jan  1 00:00:00 1970
From: will.deacon@arm.com (Will Deacon)
Date: Tue, 23 Feb 2016 20:22:33 +0000
Subject: [BUG] random kernel crashes after THP rework on s390 (maybe also
 on PowerPC and ARM)
In-Reply-To: <20160223193345.GC21820@node.shutemov.name>
References: <20160211192223.4b517057@thinkpad>
 <20160211190942.GA10244@node.shutemov.name>
 <20160211205702.24f0d17a@thinkpad>
 <20160212154116.GA15142@node.shutemov.name>
 <56BE00E7.1010303@de.ibm.com> <20160212181640.4eabb85f@thinkpad>
 <20160223103221.GA1418@node.shutemov.name>
 <20160223191907.25719a4d@thinkpad>
 <20160223193345.GC21820@node.shutemov.name>
Message-ID: <20160223202233.GE27281@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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