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Message-ID: <20150525101944.GA14095@cbox>
Date: Mon, 25 May 2015 12:19:44 +0200
From: Christoffer Dall <christoffer.dall@...aro.org>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: linux-mm@...ck.org, ebru.akagunduz@...il.com,
akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
kirill.shutemov@...ux.intel.com, riel@...hat.com, vbabka@...e.cz,
zhangyanfei@...fujitsu.com, aarcange@...hat.com,
Will Deacon <will.deacon@....com>,
Andre Przywara <andre.przywara@....com>,
Marc Zyngier <marc.zyngier@....com>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [BUG] Read-Only THP causes stalls (commit 10359213d)
On Mon, May 25, 2015 at 01:05:15PM +0300, Kirill A. Shutemov wrote:
> On Sun, May 24, 2015 at 09:34:04PM +0200, Christoffer Dall wrote:
> > Hi all,
> >
> > I noticed a regression on my arm64 APM X-Gene system a couple
> > of weeks back. I would occassionally see the system lock up and see RCU
> > stalls during the caching phase of kernbench. I then wrote a small
> > script that does nothing but cache the files
> > (http://paste.ubuntu.com/11324767/) and ran that in a loop. On a known
> > bad commit (v4.1-rc2), out of 25 boots, I never saw it get past 21
> > iterations of the loop. I have since tried to run a bisect from v3.19 to
> > v4.0 using 100 iterations as my criteria for a good commit.
> >
> > This resulted in the following first bad commit:
> >
> > 10359213d05acf804558bda7cc9b8422a828d1cd
> > (mm: incorporate read-only pages into transparent huge pages, 2015-02-11)
> >
> > Indeed, running the workload on v4.1-rc4 still produced the behavior,
> > but reverting the above commit gets me through 100 iterations of the
> > loop.
> >
> > I have not tried to reproduce on an x86 system. Turning on a bunch
> > of kernel debugging features *seems* to hide the problem. My config for
> > the XGene system is defconfig + CONFIG_BRIDGE and
> > CONFIG_POWER_RESET_XGENE.
> >
> > Please let me know if I can help test patches or other things I can
> > do to help. I'm afraid that by simply reading the patch I didn't see
> > anything obviously wrong with it which would cause this behavior.
>
> I don't see the problem on x86.
I'm wondering if we could have some weird combination of how the
specific architecture works along with these patches...
>
> Some backtraces could help to track it down.
>
I don't really get backtraces as the sytem just locks up. But here are
some of the RCU stalls as I've observed them on the console:
http://paste.ubuntu.com/11014701/
http://paste.ubuntu.com/11023143/
http://paste.ubuntu.com/11023261/
Occasionally, I also get this error from the SATA system at the moment
when I power off the device, but not sure if it is related:
ata1: exception Emask 0x10 SAct 0x0 SErr 0x180000 action 0xe frozen
ata1: irq_stat 0x00400000, PHY RDY changed
ata1: SError: { 10B8B Dispar }
Thanks,
-Christoffer
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