linux-kernel - Re: [PATCH] init,cpuset: fix initialize order

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Message-ID: <20090325135138.GG5976@nowhere>
Date:	Wed, 25 Mar 2009 14:51:39 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	miaoxie <miaox@...fujitsu.com>, Li Zefan <lizf@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <srostedt@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] init,cpuset: fix initialize order

On Wed, Mar 25, 2009 at 05:06:30PM +0800, Lai Jiangshan wrote:
> 
> (After these two fixes applied:
> [PATCH 1/2] trace_stat: keep original order
> [PATCH 2/2] trace_workqueues: fix empty line's output
> )
> When I read /debugfs/tracing/trace_stat/workqueues,
> and the I got this:
> 
> # CPU  INSERTED  EXECUTED   NAME
> # |      |         |          |
> 
>   0      0          0       cpuset
>   0    285        285       events/0
>   0      2          2       work_on_cpu/0
>   0   1115       1115       khelper
>   0    325        325       kblockd/0
>   0      0          0       kacpid
>   0      0          0       kacpi_notify
>   0      0          0       ata/0
>   0      0          0       ata_aux
>   0      0          0       ksuspend_usbd
>   0      0          0       aio/0
>   0      0          0       nfsiod
>   0      0          0       kpsmoused
>   0      0          0       kstriped
>   0      0          0       kondemand/0
>   0      1          1       hid_compat
>   0      0          0       rpciod/0
> 
>   1     64         64       events/1
>   1      2          2       work_on_cpu/1
>   1      5          5       kblockd/1
>   1      0          0       ata/1
>   1      0          0       aio/1
>   1      0          0       kondemand/1
>   1      0          0       rpciod/1
> 
> I found "cpuset" is at the earliest.
> ---------
> 
> Subject: [PATCH] init,cpuset: fix initialize order
> 
> Impact: cpuset_wq should be initialized after init_workqueues()
> 
> I found a create_singlethread_workqueue() is earlier than
> init_workqueues():
> 
> kernel_init()
> ->cpuset_init_smp()
>   ->create_singlethread_workqueue()
> ->do_basic_setup()
>   ->init_workqueues()
> 
> I think it's better that create_singlethread_workqueue() is called
> after workqueue subsystem has been initialized.
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---


Indeed it seems to be a bug.
If init_workqueues() have not been called:

- cpu_singlethread_map = NULL
- singlethread_cpu = 0

create_workqueue_thread() will be called with cpu = 0 and
then: kthread_create(worker_thread, cwq, fmt, wq->name, cpu = 0);

Meaning that cpuset is only bound to the first cpu.

Frederic.


> diff --git a/init/main.c b/init/main.c
> index 1ce6931..91d5047 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -773,6 +773,7 @@ static void __init do_basic_setup(void)
>  {
>  	rcu_init_sched(); /* needed by module_init stage. */
>  	init_workqueues();
> +	cpuset_init_smp();
>  	usermodehelper_init();
>  	driver_init();
>  	init_irq_proc();
> @@ -869,8 +870,6 @@ static int __init kernel_init(void * unused)
>  	smp_init();
>  	sched_init_smp();
>  
> -	cpuset_init_smp();
> -
>  	do_basic_setup();
>  
>  	/*
> 
> 

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