linux-kernel - Re: [PATCH 6/6] cpuset dirty limits

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Message-ID: <Pine.LNX.4.64.0709171153010.27542@schroedinger.engr.sgi.com>
Date:	Mon, 17 Sep 2007 12:00:07 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Ethan Solomita <solo@...gle.com>, linux-mm@...ck.org, pj@....com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] cpuset dirty limits

On Fri, 14 Sep 2007, Andrew Morton wrote:

> > +	mutex_lock(&callback_mutex);
> > +	*cs_int = val;
> > +	mutex_unlock(&callback_mutex);
> 
> I don't think this locking does anything?

Locking is wrong here. The lock needs to be taken before the cs pointer 
is dereferenced from the caller.

> > +	return 0;
> > +}
> > +
> >  /*
> >   * Frequency meter - How fast is some event occurring?
> >   *
> > ...
> > +void cpuset_get_current_ratios(int *background_ratio, int *throttle_ratio)
> > +{
> > +	int background = -1;
> > +	int throttle = -1;
> > +	struct task_struct *tsk = current;
> > +
> > +	task_lock(tsk);
> > +	background = task_cs(tsk)->background_dirty_ratio;
> > +	throttle = task_cs(tsk)->throttle_dirty_ratio;
> > +	task_unlock(tsk);
> 
> ditto?

It is required to take the task lock while dereferencing the tasks cpuset 
pointer.
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