linux-kernel - Re: [PATCH] lockdep: debug_show_all_locks & debug_show_held_locks vs. debug

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Date:	Thu, 22 Mar 2007 08:23:20 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jarek Poplawski <jarkao2@...pl>
Cc:	Oleg Nesterov <oleg@...sign.ru>, Neil Brown <neilb@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Folkert van Heusden <folkert@...heusden.com>,
	linux-kernel@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] lockdep: debug_show_all_locks &  debug_show_held_locks
	vs. debug_locks

On Thu, 2007-03-22 at 07:57 +0100, Jarek Poplawski wrote:
> And here is some addition.
> 
> [PATCH] lockdep: debug_show_all_locks &  debug_show_held_locks vs. debug_locks
>  
> lockdep's data shouldn't be used when debug_locks == 0
> because it's not updated after this, so it's more misleading
> than helpful.
> 
> PS: probably lockdep's current-> fields should be reset after
> it turns debug_locks off: so, after printing a bug report, but
> before return from exported functions, but there are really
> a lot of these possibilities (e.g. after DEBUG_LOCKS_WARN_ON),
> so, something could be missed. (Of course direct use of this
> fields isn't recommended either.)
> 
> Reported-by: Folkert van Heusden <folkert@...heusden.com>
> Inspired-by: Oleg Nesterov <oleg@...sign.ru>
> Signed-off-by: Jarek Poplawski <jarkao2@...pl>

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

> ---
> 
> diff -Nurp 2.6.21-rc4-git4-/kernel/lockdep.c 2.6.21-rc4-git4/kernel/lockdep.c
> --- 2.6.21-rc4-git4-/kernel/lockdep.c	2007-03-21 22:46:26.000000000 +0100
> +++ 2.6.21-rc4-git4/kernel/lockdep.c	2007-03-21 23:05:17.000000000 +0100
> @@ -2742,6 +2742,10 @@ void debug_show_all_locks(void)
>  	int count = 10;
>  	int unlock = 1;
>  
> +	if (unlikely(!debug_locks)) {
> +		printk("INFO: lockdep is turned off.\n");
> +		return;
> +	}
>  	printk("\nShowing all locks held in the system:\n");
>  
>  	/*
> @@ -2785,6 +2789,10 @@ EXPORT_SYMBOL_GPL(debug_show_all_locks);
>  
>  void debug_show_held_locks(struct task_struct *task)
>  {
> +	if (unlikely(!debug_locks)) {
> +		printk("INFO: lockdep is turned off.\n");
> +		return;
> +	}
>  	lockdep_print_held_locks(task);
>  }
>  

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