linux-kernel - Re: [PATCH] printk: fix one circular lockdep warning about console

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Date:	Thu, 20 Mar 2014 14:15:48 +0800
From:	Jane Li <jiel@...vell.com>
To:	Jan Kara <jack@...e.cz>
CC:	Andrew Morton <akpm@...ux-foundation.org>, <joe@...ches.com>,
	<tj@...nel.org>, <fweisbec@...il.com>, <davem@...emloft.net>,
	<keescook@...omium.org>, <linux-kernel@...r.kernel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	"jiel@...vell.com" <"Jane Li"@mx0b-0016f401.pphosted.com>
Subject: Re: [PATCH] printk: fix one circular lockdep warning about console_lock

On 03/19/2014 06:00 PM, Jan Kara wrote:

> On Wed 19-03-14 11:08:08, Jane Li wrote:
>> On 02/12/2014 05:19 AM, Andrew Morton wrote:
>>> On Tue, 11 Feb 2014 14:50:00 +0800<jiel@...vell.com>  wrote:
>   Umm, I disagree with the patch. What I proposed in my answer to your patch is something like the patch below. Does it fix your problem?
>
> 								Honza
>
> From 91497a88c403a7f22e78fee2f69d7413c6e8209f Mon Sep 17 00:00:00 2001
> From: Jan Kara <jack@...e.cz>
> Date: Wed, 19 Mar 2014 10:56:12 +0100
> Subject: [PATCH] printk: Fixup lockdep annotation in console_suspend()
>
> Although console_suspend() releases console_sem, it doesn't tell lockdep about it. That results in the lockdep warning about circular locking when doing the following:
>   enter suspend ->  resume ->  plug-out CPUx (echo 0 > cpux/online)
>
> Fix the problem by telling lockdep we actually released the semaphore in
> console_suspend() and acquired it again in console_resume().
>
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
>  kernel/printk/printk.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 4dae9cbe9259..e6ada322782b 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1880,6 +1880,7 @@ void suspend_console(void)
>  	console_lock();
>  	console_suspended = 1;
>  	up(&console_sem);
> +	mutex_release(&console_lock_dep_map, 1, _RET_IP_);
>  }
>  
>  void resume_console(void)
> @@ -1887,6 +1888,7 @@ void resume_console(void)
>  	if (!console_suspend_enabled)
>  		return;
>  	down(&console_sem);
> +	mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);
>  	console_suspended = 0;
>  	console_unlock();
>  }
> --
> 1.8.1.4

Oh, yes, this new solution works well. If run same test, no circular lockdep warning occurs now. I will update patch v2.

Sorry for misunderstanding your answer before.

Thanks!

Best Regards,

Jane


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