linux-kernel - Re: [PATCH -tip 2/2] sched: Display autogroup names in /proc/sched

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Message-ID: <20110110100917.GH2772@in.ibm.com>
Date:	Mon, 10 Jan 2011 15:39:17 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Mike Galbraith <efault@....de>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH -tip 2/2] sched: Display autogroup names in
 /proc/sched_debug.

On Mon, Jan 10, 2011 at 10:38:07AM +0100, Mike Galbraith wrote:
> On Mon, 2011-01-10 at 10:46 +0530, Bharata B Rao wrote:
> > sched: Display autogroup names in /proc/sched_debug.
> > 
> > Add autogroup name to cfs_rq and tasks information in /proc/sched_debug.
> > 
> > Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> > ---
> >  kernel/sched_debug.c |    8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > --- a/kernel/sched_debug.c
> > +++ b/kernel/sched_debug.c
> > @@ -92,6 +92,14 @@ static void print_cfs_group_stats(struct
> >  #ifdef CONFIG_CGROUP_SCHED
> >  static char * task_group_path(struct task_group *tg)
> >  {
> > +#ifdef CONFIG_SCHED_AUTOGROUP
> > +	int enabled = ACCESS_ONCE(sysctl_sched_autogroup_enabled);
> > +
> > +	if (enabled && tg->autogroup) {
> > +		autogroup_path(tg, group_path, PATH_MAX);
> > +		return group_path;
> > +	}
> > +#endif
> >  	/*
> >  	 * May be NULL if the underlying cgroup isn't fully-created yet
> >  	 */
> 
> What prevents the task being moved, and the task group being freed under
> you?  Looks to me like task_group_path() needs rcu_read_lock().  It is
> locked in the other two instances.  How about the below?

You are right, we need rcu_read_lock() there. Let me spin out an other
version with the changes.

Thanks,
Bharata.
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