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

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Date:	Fri, 03 Jun 2011 13:52:06 +0200
From:	Arne Jansen <lists@...-jansens.de>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.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 03.06.2011 12:30, Peter Zijlstra wrote:
> On Fri, 2011-06-03 at 12:02 +0200, Arne Jansen wrote:
>> On 03.06.2011 11:15, Peter Zijlstra wrote:
> 
> Bummer.
> 
>>  but the hang is not as complete as I first
>> thought. A running iostat via ssh continues to give output for a while,
>> the serial console still reacts to return and prompts for login. But
>> after a while more and more locks up. The console locks as soon as I
>> sysrq-t.
> 
> OK, that seems to suggest one CPU is stuck, and once you try something
> that touches the CPU everything grinds to a halt. Does something like
> sysrq-l work? That would send NMIs to the other CPUs.
> 
> Anyway, good to know using serial doesn't make it go away, that means
> its not too timing sensitive.
> 
> 
>> Also the 10k-print gets triggered
>> several times (though I only see 10 lines of output). Maybe you can
>> send me your test-module and I'll try that, so we have more equal
>> conditions.
> 
> Sure, see below.
> 

Your module also triggers it. On first test directly on first try, on
second test only on the 3rd try. When it hangs sysrq-l doesn't give
any output. I double checked without a hang, and then it dumps
something.


>> What also might help: the maschine I'm testing with is a quad-core
>> X3450 with 8GB RAM.
> 
> /me & wikipedia, that's a nehalem box, ok I'm testing on a westmere
> (don't have a nehalem).


> 
> ---
>  kernel/Makefile |    1 +
>  kernel/test.c   |   23 +++++++++++++++++++++++
>  2 files changed, 24 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 2d64cfc..65eff6c 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -80,6 +80,7 @@ obj-$(CONFIG_LOCKUP_DETECTOR) += watchdog.o
>  obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
>  obj-$(CONFIG_SECCOMP) += seccomp.o
>  obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
> +obj-m += test.o
>  obj-$(CONFIG_TREE_RCU) += rcutree.o
>  obj-$(CONFIG_TREE_PREEMPT_RCU) += rcutree.o
>  obj-$(CONFIG_TREE_RCU_TRACE) += rcutree_trace.o
> diff --git a/kernel/test.c b/kernel/test.c
> index e69de29..8005395 100644
> --- a/kernel/test.c
> +++ b/kernel/test.c
> @@ -0,0 +1,23 @@
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +
> +MODULE_LICENSE("GPL");
> +
> +static void
> +test_cleanup(void)
> +{
> +}
> +
> +static int __init
> +test_init(void)
> +{
> +	int i;
> +
> +	for (i = 0; i < 10000; i++)
> +		printk("test %d\n", i);
> +
> +	return 0;
> +}
> +
> +module_init(test_init);
> +module_exit(test_cleanup);
> 

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