linux-kernel - Re: Where is RLIMIT_RT

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Date:	Sun, 16 Jul 2006 11:44:31 +0100 (BST)
From:	Esben Nielsen <nielsen.esben@...glemail.com>
To:	Jean-Marc Valin <Jean-Marc.Valin@...erbrooke.ca>
cc:	Lee Revell <rlrevell@...-job.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Esben Nielsen <nielsen.esben@...glemail.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: Where is RLIMIT_RT_CPU?

On Sun, 16 Jul 2006, Jean-Marc Valin wrote:

>> I don't think it's a problem.  If the admin does not want non-root users
>> to be able to lock up the machine, just don't put them in the realtime
>> group.
>
> What if the admin *wants* non-root users to have good quality audio, and
> just doesn't want them to crash the system (voluntarily and especially
> accidentally). Enforcing CPU limits *is* possible and it has already
> been done independently by both Ingo and Con. I'm just waiting for the
> feature to be available out-of-the box, which is not for today if kernel
> space keeps pointing at userspace and vice versa. :-(
>
> 	Jean-Marc
>

You can't have "random" users scheduling thing at real-time priorities.
A real-time system can only work if it is set up as whole and all 
real-time tasks are taken into consideration. If you allow a user to start 
another real-time task, that task might destroy the real-time properties 
of all the rest by taking too much cpu.

As I see it the only thing you can do is to use sudo to run anything,
which needs real-time priority, with higher priviliges, than what a normal 
user have. Then he can only start specific audio programs and can't crash 
the system (unless those programs have a bug).

Esben
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