linux-kernel - Re: [PATCH] sched: Don't allow priority switch to realtime when the task doesn't belong to init_task_group and when CONFIG_RT_GROUP

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Message-ID: <20081120081924.GB4349@in.ibm.com>
Date:	Thu, 20 Nov 2008 13:49:24 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
Subject: Re: [PATCH] sched: Don't allow priority switch to realtime when
	the task doesn't belong to init_task_group and when
	CONFIG_RT_GROUP_SCHED isn't set

On Thu, Nov 20, 2008 at 08:58:29AM +0100, Ingo Molnar wrote:
> <snip>
> hm, another option would be, instead of denying something (which 
> denial might not even be noticed by the app) that the app clearly has 
> enough privilege to request - to just act upon it and move the task to 
> the init_task_group?

Thought about that option, but decided against it because:

- The task was started in a group which is not "equipped" to handle
  rt tasks (no rt_rq for the group because CONFIG_RT_GROUP_SCHED=n). So
  the task shouldn't have been started in such a group in the first
  place.
- We could move the task silently to init_task_group (which is kind
  of done now with the task being placed in init_task_group's rq), but
  that's not what a user would have expected when he started a task
  under a group.

Also, silently moving the task to init_task_group would cause confusion
later when the task drops the RT privilege. As Dhaval is asking in the
other thread, which group do we move it to now ?

Regards,
Bharata.
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