linux-kernel - Re: [RFC][PATCH 2/4] Revert Changes to kernel/workqueue.c

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Date:	Thu, 24 Aug 2006 16:33:06 +0530
From:	Dipankar Sarma <dipankar@...ibm.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Gautham R Shenoy <ego@...ibm.com>, rusty@...tcorp.com.au,
	torvalds@...l.org, akpm@...l.org, linux-kernel@...r.kernel.org,
	arjan@...el.linux.com, mingo@...e.hu, davej@...hat.com,
	vatsa@...ibm.com, ashok.raj@...el.com
Subject: Re: [RFC][PATCH 2/4] Revert Changes to kernel/workqueue.c

On Thu, Aug 24, 2006 at 12:51:00PM +0200, Heiko Carstens wrote:
> > @@ -510,13 +515,11 @@ int schedule_on_each_cpu(void (*func)(vo
> >  	if (!works)
> >  		return -ENOMEM;
> >  
> > -	mutex_lock(&workqueue_mutex);
> >  	for_each_online_cpu(cpu) {
> >  		INIT_WORK(per_cpu_ptr(works, cpu), func, info);
> >  		__queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu),
> >  				per_cpu_ptr(works, cpu));
> >  	}
> > -	mutex_unlock(&workqueue_mutex);
> >  	flush_workqueue(keventd_wq);
> >  	free_percpu(works);
> >  	return 0;
> 
> Removing this lock without adding a lock/unlock_cpu_hotplug seems wrong,
> since this function is walking the cpu_online_map.

As long as you disable preemption and don't block the critical
section should be safe from cpu hotplug. There is no need to 
lock/unlock cpu hotplug.

Thanks
Dipankar
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