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

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Date:	Wed, 01 Jun 2011 18:35:20 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Arne Jansen <lists@...-jansens.de>
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 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?

Because those 10k lines aren't even near the amount of crap a regular
boot spews out on this box, although I guess the tight loop might
generate it slightly faster than a regular boot does.

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