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

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Message-Id: <200912160911.43201.rusty@rustcorp.com.au>
Date:	Wed, 16 Dec 2009 09:11:42 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Tejun Heo <tj@...nel.org>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [this_cpu_xx V7 7/8] Module handling: Use this_cpu_xx to dynamically allocate counters

On Tue, 15 Dec 2009 02:33:50 pm Tejun Heo wrote:
> (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().

Yes.

Thanks,
Rusty.
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