linux-kernel - Re: [PATCH, v6 2/3] Implement timer slack notifier chain

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Message-ID: <20110214145244.GB3666@shutemov.name>
Date:	Mon, 14 Feb 2011 16:52:44 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Paul Menage <menage@...gle.com>, Li Zefan <lizf@...fujitsu.com>,
	containers@...ts.linux-foundation.org,
	jacob.jun.pan@...ux.intel.com,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Matt Helsley <matthltc@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-api@...r.kernel.org
Subject: Re: [PATCH, v6 2/3] Implement timer slack notifier chain

On Mon, Feb 14, 2011 at 02:32:23PM +0100, Thomas Gleixner wrote:
> On Mon, 14 Feb 2011, Kirill A. Shutsemov wrote:
> 
> > From: Kirill A. Shutemov <kirill@...temov.name>
> > 
> > Process can change its timer slack using prctl(). Timer slack notifier
> > call chain allows to react on such change or forbid it.
> 
> So we add a notifier call chain and more exports to allow what ?

To allow the cgroup contoller validate the value.

> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -1691,15 +1691,10 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> >  			error = perf_event_task_enable();
> >  			break;
> >  		case PR_GET_TIMERSLACK:
> > -			error = current->timer_slack_ns;
> > +			error = prctl_get_timer_slack();
> 
>   What's the point of replacing current->timer_slack_ns with a
>   function which does exactly the same ?

To keep it consistent. BTW, prctl_get_seccomp() does the same.

> 
> > +long prctl_set_timer_slack(long timer_slack_ns)
> > +{
> > +	int err;
> > +
> > +	/* Reset timer slack to default value */
> > +	if (timer_slack_ns <= 0) {
> > +		current->timer_slack_ns = current->default_timer_slack_ns;
> > +		return 0;
> 
>   That does not make any sense at all. Why is setting
>   default_timer_slack_ns not subject to validation ?

Hm.. In case of cgroup_timer_slack it's always valid.
But, yes, in general, we should validate it.

>   Why is it treaded seperately ?

What do you mean?

> > +	}
> > +
> > +	err = blocking_notifier_call_chain(&timer_slack_notify_list,
> > +			timer_slack_ns, NULL);
> > +	if (err == NOTIFY_DONE)
> > +		current->timer_slack_ns = timer_slack_ns;
> > +
> > +	return notifier_to_errno(err);
> 
> Thanks,
> 
> 	tglx

-- 
 Kirill A. Shutemov
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