linux-kernel - Re: [tip:sched/locking] sched: Add p->pi_lock to task_rq

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Date:	Wed, 01 Jun 2011 21:30:55 +0200
From:	Arne Jansen <lists@...-jansens.de>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, efault@....de, npiggin@...nel.dk,
	akpm@...ux-foundation.org, frank.rowand@...sony.com,
	tglx@...utronix.de, mingo@...e.hu,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/locking] sched: Add p->pi_lock to task_rq_lock()

On 01.06.2011 20:44, Peter Zijlstra wrote:
> On Wed, 2011-06-01 at 20:09 +0200, Peter Zijlstra wrote:
>> On Wed, 2011-06-01 at 19:20 +0200, Arne Jansen wrote:
>>> On 01.06.2011 18:35, Peter Zijlstra wrote:
>>>> On Wed, 2011-06-01 at 15:58 +0200, Arne Jansen wrote:
>>>>> git bisect blames this commit for a problem I have with v3.0-rc1:
>>>>> If I printk large amounts of data, the machine locks up.
>>>>> As the commit does not revert cleanly on top of 3.0, I haven't been
>>>>> able to double check.
>>>>> The test I use is simple, just add something like
>>>>>
>>>>> for (i=0; i<   10000; ++i) printk("test %d\n", i);
>>>>>
>>>>> and trigger it, in most cases I can see the first 10 printks before
>>>>> I have to power cycle the machine (sysrq-b does not work anymore).
>>>>> Attached my .config.
>>>>
>>>> I've made me a module that does the above, I've also changed my .config
>>>> to match yours (smp=y, sched-cgroup=y, autogroup=n, preempt=n, no_hz=y),
>>>> but sadly I cannot reproduce, I get all 10k prints on my serial line.
>>>>
>>>> Even without serial line it works (somehow booting without visible
>>>> console is scary as hell :)
>>>>
>>>> Which makes me ask, how are you observing your console?
>>>>
>>>
>>> They don't go out to the serial line, I only observe them with a
>>> tail -f on messages. Default log level doesn't go the console here.
>>
>> Right ok, so I used your exact .config, added a few drivers needed for
>> my hardware and indeed, it doesn't even finish booting and gets stuck
>> someplace.
>>
>> Sadly it looks like even the NMI watchdog is dead,.. /me goes try and
>> make sense of this.
>
> Sadly both 0122ec5b02f766c355b3168df53a6c038a24fa0d^1 and
> 0122ec5b02f766c355b3168df53a6c038a24fa0d itself boot just fine and run
> the test module without problems.

I can only partially confirm this:

2acca55ed98ad9b9aa25e7e587ebe306c0313dc7 runs fine
0122ec5b02f766c355b3168df53a6c038a24fa0d freezes after line 189
ab2515c4b98f7bc4fa11cad9fa0f811d63a72a26 freezes after line 39

>
> I will have to re-bisect this.
>
> --
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