linux-kernel - Re: [PATCH -rt 5/5] slub: -rt port

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Message-Id: <1184435417.5284.58.camel@lappy>
Date:	Sat, 14 Jul 2007 19:50:17 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Steven Rostedt <rostedt@...dmis.org>,
	Christoph Lameter <clameter@....com>
Subject: Re: [PATCH -rt 5/5] slub: -rt port

On Sat, 2007-07-14 at 21:39 +0400, Oleg Nesterov wrote:
> On 07/14, Peter Zijlstra wrote:
> >
> > +static void flush_all(struct kmem_cache *s)
> > +{
> > +	int cpu;
> > +	struct workqueue_struct *wq = flush_slab_workqueue;
> > +
> > +	mutex_lock(&flush_slab_mutex);
> > +	for_each_online_cpu(cpu) {
> > +		struct slab_work_struct *sw = &per_cpu(slab_works, cpu);
> > +
> > +		INIT_WORK(&sw->work, flush_cpu_slab_wq);
> > +		sw->s = s;
> > +		queue_work_cpu(wq, &sw->work, cpu);
> > +	}
> > +	flush_workqueue(wq);
> > +	mutex_unlock(&flush_slab_mutex);
> > +}
> 
> I suspect this is not cpu-hotplug safe. flush_slab_mutex doesn't protect
> from cpu_down(). This means that slab_work_struct could be scheduled on
> the already dead CPU. flush_workqueue(wq) will hang in that case.

Yeah, the function I copied this from: schedule_on_each_cpu() has a
comment to that effect.

Any ideas on how to solve this?

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