linux-kernel - Re: still nfs problems [Was: Linux 2.6.37-rc8]

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Date:	Wed, 05 Jan 2011 16:01:30 +0100
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	Trond Myklebust <Trond.Myklebust@...app.com>
CC:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-nfs@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Marc Kleine-Budde <m.kleine-budde@...gutronix.de>
Subject: Re: still nfs problems [Was: Linux 2.6.37-rc8]

On 01/05/2011 03:53 PM, Trond Myklebust wrote:
> On Wed, 2011-01-05 at 14:40 +0100, Uwe Kleine-König wrote: 
>> Hi Russell,
>>
>> On Wed, Jan 05, 2011 at 11:27:01AM +0000, Russell King - ARM Linux wrote:
>>> On Wed, Jan 05, 2011 at 12:05:17PM +0100, Uwe Kleine-König wrote:
>>>> Hello Trond,
>>>>
>>>> On Wed, Jan 05, 2011 at 09:40:14AM +0100, Uwe Kleine-König wrote:
>>>>> On Mon, Jan 03, 2011 at 07:22:38PM -0500, Trond Myklebust wrote:
>>>>>> The question is whether this is something happening on the server or the
>>>>>> client. Does an older client kernel boot without any trouble?
>>>>> I will set up a boot test with 2.6.37 (for statistics) and 2.6.36 to
>>>>> compare with.  If you don't consider .36 to be old enough let me now.
>>>>> Once the setup is done it should be easy to test .35 (say), too.
>>>>>
>>>> Marc (cc'd) saw similar[1] problems with .37, when using .36.2 the
>>>> problems didn't occur.  This was more reliable to trigger and he was so
>>>> kind to bisect the problem.
>>>>
>>>> When testing v2.6.36-rc3-51-gafa8ccc init hanged.
>>>> (babddc72a9468884ce1a23db3c3d54b0afa299f0 is the first bad commit with
>>>> this hang.)  Commit 56e4ebf877b6043c289bda32a5a7385b80c17dee makes the
>>>> "init hangs" problem the "fileid changed on tab" problem.
>>>>
>>>> I could only reproduce that on armv5 machines (imx27, imx28 and at91)
>>>> but not on armv6 (imx35).
>>>
>>> FYI, I've seen the "fileid changed" problem, and it looked like a 32-bit
>>> truncation of the fileid.  It occurred several times on successive
>>> reboots, so I tried to capture a tcpdump trace off the server (Linux
>>> 2.6.23-rc8-ga64314e6 - its ancient because I've had issues with buggy
>>> IDE drivers trying to move it forward.)  However, for the last couple
>>> of weeks I've been unable to reproduce it.
>>>
>>> The client was based on 2.6.37-rc6.
>>>
>>> The "fileid changed" messages popped up after mounting an export with
>>> 'nolock,intr,rsize=4096,soft', and then trying to use bash completion
>>> and 'ls' in a few subdirectories - and entries were missing from the
>>> directory lists without 'ls' reporting any errors (which I think is bad
>>> behaviour in itself.)
>> There was a bug in at least -rc5[1] that was considered already fixed in
>> -rc4[2]. The later announcements didn't mention it anymore. 
>>
>>> I don't know why it's stopped producing the errors, although once it
>>> went I never investigated it any further (was far too busy trying to
>>> get AMBA DMA support working.)
>> It seems it was fixed for most users though. Trond?
> 
> As I said, I can't reproduce it.
> 
> I'm seeing a lot of mention of ARM above. Is anyone seeing this bug on
> x86, or does it appear to be architecture-specific?

It _seems_ to be ARMv5 specific[1]. Uwe did some tests and figured out
that disabling dcache on ARMv5 "fixes" the problem, but
CONFIG_CPU_DCACHE_WRITETHROUGH isn't enough.

[1] Uwe fails to reproduce it on ARMv6. The ARMv6 has a L2 cache and
uses IIRC different instructions to flush the L1 caches. (please correct
me, if I'm wrong, ARM guys :)

cheers, Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |


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