linux-kernel - Re: [patch] lockdep: more unlock-on-error fixes

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Date:	Tue, 19 Dec 2006 08:21:34 +0100
From:	Jarek Poplawski <jarkao2@...pl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [patch] lockdep: more unlock-on-error fixes

On Mon, Dec 18, 2006 at 03:39:36PM +0100, Ingo Molnar wrote:
> 
> * Jarek Poplawski <jarkao2@...pl> wrote:
> 
> > Hello,
> > 
> > If any of this proposals should be omitted or separated let me know.
> 
> thanks for the fixes, they look good to me. I have reorganized the 
> __lock_acquire() changes a bit. Plus i dropped the check_locks_freed() 
> changes: there's no reason lockdep should be using 'raw' irq flags 
> saving - these functions are not part of the irq-flags tracing code so 
> they dont /need/ to be raw.

I'm not 100% convinced - now trace_hardirqs_off/on is 
done only for lockdep reasons, so it is like selfcheck.
But it's probably the matter of taste.

...
> Index: linux/kernel/lockdep.c
> ===================================================================
> --- linux.orig/kernel/lockdep.c
> +++ linux/kernel/lockdep.c
...
> @@ -2210,19 +2214,24 @@ out_calc_hash:
>  		if (!chain_head && ret != 2)
>  			if (!check_prevs_add(curr, hlock))
>  				return 0;
> -		graph_unlock();
> -	}
> +	} else
> +		/* after lookup_chain_cache(): */
> +		if (unlikely(!debug_locks))
> +			return 0;
> +
>  	curr->lockdep_depth++;
>  	check_chain_key(curr);
>  	if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) {
> -		debug_locks_off();
> +		debug_locks_off_graph_unlock();
>  		printk("BUG: MAX_LOCK_DEPTH too low!\n");
>  		printk("turning off the locking correctness validator.\n");
>  		return 0;
>  	}
> +
>  	if (unlikely(curr->lockdep_depth > max_lockdep_depth))
>  		max_lockdep_depth = curr->lockdep_depth;
>  
> +	graph_unlock();
>  	return 1;
>  }

Sorry but it's not good... There could be no lock 
at all here (eg. trylock != 0 || check != 2). 

Jarek P.
-
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