Re: [stable] [PATCH] lockdep: fix mismatched lockdep_depth/curr_chain_hash

[Greg KH <greg@kroah.com>]

On Fri, Oct 05, 2007 at 11:31:26AM +0200, Peter Zijlstra wrote:
> 
> Stable team,
> 
> please consider this patch for the next 22-stable.

I don't see this patch in Linus's upstream tree.  We need it there to be
able to accept it for -stable.  Or is this just a bugfix of other things
that are already in his tree?

thanks,

greg k-h


> 
> ---
> Subject: lockdep: fix mismatched lockdep_depth/curr_chain_hash
> From: Gregory Haskins <ghaskins@novell.com>
> 
> It is possible for the current->curr_chain_key to become inconsistent with the
> current index if the chain fails to validate.  The end result is that future
> lock_acquire() operations may inadvertently fail to find a hit in the cache
> resulting in a new node being added to the graph for every acquire.
> 
> [ peterz: this might explain some of the lockdep is so _slow_ complaints. ]
> [ mingo: this does not impact the correctness of validation, but may slow
>   down future operations significantly, if the chain gets very long. ]
> 
> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> ---
>  kernel/lockdep.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/kernel/lockdep.c
> ===================================================================
> --- linux-2.6.orig/kernel/lockdep.c
> +++ linux-2.6/kernel/lockdep.c
> @@ -2166,7 +2166,6 @@ out_calc_hash:
>  	}
>  #endif
>  	chain_key = iterate_chain_key(chain_key, id);
> -	curr->curr_chain_key = chain_key;
>  
>  	/*
>  	 * Trylock needs to maintain the stack of held locks, but it
> @@ -2215,6 +2214,7 @@ out_calc_hash:
>  		if (unlikely(!debug_locks))
>  			return 0;
>  
> +	curr->curr_chain_key = chain_key;
>  	curr->lockdep_depth++;
>  	check_chain_key(curr);
>  #ifdef CONFIG_DEBUG_LOCKDEP
> 
> 
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