linux-kernel - Re: allow non root users to set io priority "idle" ?

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Date:	Wed, 8 Aug 2007 12:20:56 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Sheplyakov Alexei <varg@...or.jinr.ru>
Cc:	Andi Kleen <andi@...stfloor.org>, dragoran <drago01@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: allow non root users to set io priority "idle" ?

On Wed, Aug 08, 2007 at 01:51:32PM +0400, Sheplyakov Alexei wrote:
> On Mon, Aug 06, 2007 at 01:11:01PM +0200, Andi Kleen wrote:
> 
> > Very low priority can starve others when it holds some kernel resource
> > needed by another task.  
> 
> Nevertheless ordinary users are permitted to lower priority ([re]nice)

Low priority as allowed by renice is ok -- the resource holder will 
run eventually and the system make progress.

> I don't quite understand. There are a lot of other ways to starve such
> high-priority process: 
> 1. renice the low-priority process

That requires user action.

e.g. if you google a bit you can find a famous story where the NASA
had to do that remotely to solve a PI problem on one of the Mars rovers. But I'm
sure they weren't very pleased about it. And not everybody has a JPL
control room to patch things up in the backhand.

> 2. send it a signal
> 3. ptrace it

Only root can do these.

-Andi

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