linux-kernel - Re: [tip:core/locking 2/3] lockdep:define preallocated "stack" for BFS as per cpu variable

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Message-Id: <1248267830.27058.1404.camel@twins>
Date:	Wed, 22 Jul 2009 15:03:50 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	tom.leiming@...il.com
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mingo@...e.hu, torvalds@...ux-foundation.org
Subject: Re: [tip:core/locking 2/3] lockdep:define preallocated "stack" for
 BFS as per cpu variable

On Wed, 2009-07-22 at 20:58 +0800, tom.leiming@...il.com wrote:
> From: Ming Lei <tom.leiming@...il.com>

This patch can use a changelog.

Why is this needed, isn't all that serialized by the graph_lock anyway?
Or are there a few paths where this isn't the case and we're now racy?

> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> ---
>  kernel/lockdep.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/lockdep.c b/kernel/lockdep.c
> index 1b1796a..1583439 100644
> --- a/kernel/lockdep.c
> +++ b/kernel/lockdep.c
> @@ -847,7 +847,7 @@ struct circular_queue {
>  	unsigned int  front, rear;
>  };
>  
> -static struct circular_queue lock_cq;
> +static DEFINE_PER_CPU(struct circular_queue, lock_cq);
>  
>  unsigned int max_bfs_queue_depth;
>  
> @@ -937,7 +937,7 @@ static int __bfs(struct lock_list *source_entry,
>  {
>  	struct lock_list *entry;
>  	struct list_head *head;
> -	struct circular_queue *cq = &lock_cq;
> +	struct circular_queue *cq = &get_cpu_var(lock_cq);
>  	int ret = 1;
>  
>  	if (match(source_entry, data)) {
> @@ -993,6 +993,7 @@ static int __bfs(struct lock_list *source_entry,
>  		}
>  	}
>  exit:
> +	put_cpu_var(lock_cq);
>  	return ret;
>  }
>  

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