linux-kernel - Re: [PATCH 2/2] sched: allow users with rtprio rlimit to change from SCHED

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Date:	Wed, 23 Feb 2011 12:35:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Darren Hart <dvhart@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	richard.purdie@...uxfoundation.org
Subject: Re: [PATCH 2/2] sched: allow users with rtprio rlimit to change from
 SCHED_IDLE policy


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, 2011-02-23 at 12:13 +0100, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > On Tue, 2011-02-22 at 13:04 -0800, Darren Hart wrote:
> > > > As it stands, users with rtprio rlimit permissions can change their policy from
> > > > SCHED_OTHER to SCHED_FIFO and back. They can change to SCHED_IDLE, but not back
> > > > to SCHED_FIFO. If they have the rtprio permission, they should be able to. Once
> > > > in SCHED_FIFO, they could go back to SCHED_OTHER. This patch allows users with
> > > > rtprio permission to change out of SCHED_IDLE.
> > > > 
> > > 
> > > Ingo, can you remember the rationale for this?
> > > 
> > > The fact is that SCHED_IDLE is very near nice-20, and we can do:
> > > 
> > > peterz@...ns:~$ renice 5 -p $$
> > > 1867: old priority 0, new priority 5
> > > peterz@...ns:~$ renice 0 -p $$
> > > 1867: old priority 5, new priority 0
> > > 
> > > Which would suggest that we should be able to return to SCHED_OTHER
> > > RLIMIT_NICE-20.
> > 
> > I dont remember anything subtle there - most likely we just forgot about that spot 
> > when adding RLIMIT_RTPRIO support.
> 
> Ah, I was arguing we should allow it regardless of RLIMIT_RTPRIO, based on 
> RLIMIT_NICE, it is after all a change to SCHED_OTHER, not SCHED_FIFO/RR.

Sure. We just went for the most restrictive conditions - it's hard to add security 
holes that way ;-)

	Ingo
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