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

Kirill A. Shutemov
2011-02-14T14:52:44Z

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-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>
> >
> > 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