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Subject: Re: [patch] Re: autogroup: sched_setscheduler() fails
From: Mike Galbraith <efault@gmx.de>
To: Yong Zhang <yong.zhang0@gmail.com>
Cc: bharata@linux.vnet.ibm.com, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
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Date: Thu, 13 Jan 2011 07:13:08 +0100
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On Thu, 2011-01-13 at 13:59 +0800, Yong Zhang wrote:
> On Thu, Jan 13, 2011 at 11:54 AM, Mike Galbraith <efault@gmx.de> wrote:
> > sched, autogroup: fix CONFIG_RT_GROUP_SCHED sched_setscheduler() failure.
> >
> > If CONFIG_RT_GROUP_SCHED is set, __sched_setscheduler() fails due to autogroup
> > not allocating rt_runtime.  Free unused/unusable rt_se and rt_rq, redirect RT
> > tasks to the root task group, and tell __sched_setscheduler() that it's ok.
> >
> > Signed-off-by: Mike Galbraith <efault@gmx.de>
> > Reported-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> 
> This looks more clear ;)
> 
> And a little comment below
> 
> >
> > ---
> >  kernel/sched.c           |    3 ++-
> >  kernel/sched_autogroup.c |   27 +++++++++++++++++++++++++++
> >  kernel/sched_autogroup.h |    4 ++++
> >  3 files changed, 33 insertions(+), 1 deletion(-)
> > @@ -106,6 +128,11 @@ task_wants_autogroup(struct task_struct
> >        return true;
> >  }
> >
> > +static inline bool task_group_is_autogroup(struct task_group *tg)
> > +{
> > +       return tg != &root_task_group && tg->autogroup;
> 
> Isn't just checking tg->autogroup sufficient?
> 
> if tg == &root_task_group
> 
> > --- linux-2.6.orig/kernel/sched.c
> > +++ linux-2.6/kernel/sched.c
> > @@ -4874,7 +4874,8 @@ recheck:
> >                 * assigned.
> >                 */
> >                if (rt_bandwidth_enabled() && rt_policy(policy) &&
> > -                               task_group(p)->rt_bandwidth.rt_runtime == 0) {
> > +                               task_group(p)->rt_bandwidth.rt_runtime == 0 &&
> 
> this check will fail.

Yes, it's intended to fail.  I intend to make it explicit throughout
autogroup that root_task_group is not an autogroup, and will drop the
test for root_task_group then.

	-Mike