linux-kernel - Re: [this_cpu_xx V7 7/8] Module handling: Use this_cpu

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Date:	Tue, 15 Dec 2009 13:03:50 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [this_cpu_xx V7 7/8] Module handling: Use this_cpu_xx to dynamically
 allocate counters

(Rusty Russell cc'd.)

On 12/15/2009 07:03 AM, Christoph Lameter wrote:
> @@ -479,15 +467,15 @@ static inline int try_module_get(struct 
>  	int ret = 1;
>  
>  	if (module) {
> -		unsigned int cpu = get_cpu();
>  		if (likely(module_is_live(module))) {
> -			local_inc(__module_ref_addr(module, cpu));
> +			preempt_disable();
> +			__this_cpu_inc(module->refptr->count);
>  			trace_module_get(module, _THIS_IP_,
> -				local_read(__module_ref_addr(module, cpu)));
> +				__this_cpu_read(module->refptr->count));
> +			preempt_enable();
>  		}
>  		else
>  			ret = 0;
> -		put_cpu();

I think you need preemption disabled while checking whether
module_is_live().  The state is protected by stop_machine or
synchronize_sched().

Thanks.

-- 
tejun
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