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SubjectRe: [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@marvell.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@suse.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@suse.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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