linux-kernel - Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

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Date:	Fri, 12 Feb 2016 15:52:22 +0000
From:	Will Deacon <will.deacon@....com>
To:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	linuxppc-dev@...ts.ozlabs.org,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Paul Mackerras <paulus@...ba.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also
 on PowerPC and ARM)

On Fri, Feb 12, 2016 at 11:12:34AM +0100, Sebastian Ott wrote:
> On Fri, 12 Feb 2016, Will Deacon wrote:
> > On Thu, Feb 11, 2016 at 08:57:02PM +0100, Gerald Schaefer wrote:
> > > On Thu, 11 Feb 2016 21:09:42 +0200
> > > "Kirill A. Shutemov" <kirill@...temov.name> wrote:
> > > > On Thu, Feb 11, 2016 at 07:22:23PM +0100, Gerald Schaefer wrote:
> > > > > Sebastian Ott reported random kernel crashes beginning with v4.5-rc1 and
> > > > > he also bisected this to commit 61f5d698 "mm: re-enable THP". Further
> > > > > review of the THP rework patches, which cannot be bisected, revealed
> > > > > commit fecffad "s390, thp: remove infrastructure for handling splitting PMDs"
> > > > > (and also similar commits for other archs).

[...]

> > Do you have a reliable way to trigger the "random kernel crashes"? We've not
> > seen anything reported on arm64, but I don't see why we wouldn't be affected
> > by the same bug and it would be good to confirm and validate a fix.
> 
> My testcase was compiling the kernel. Most of the time my test system
> didn't survive a single compile run. During bisect I did at least 20
> compile runs to flag a commit as good.

I've been building kernels all day with -rc3 on my arm64 box and haven't
seen any problems yet.. :/.

I'll leave it going over the weekend.

Will