On Tue, 2010-11-16 at 14:59 +0100, Peter Zijlstra wrote:
quoted text
> On Mon, 2010-11-15 at 17:55 -0800, Paul Menage wrote:
> > On Mon, Nov 15, 2010 at 5:18 PM, Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > so sched_debug_show() is apparently calling cgroup_path() with a NULL
> > > cgroup. I think it's "print_task()" that is to blame, it does
> > >
> > >     cgroup_path(task_group(p)->css.cgroup, ..
> > >
> > > without checking whether there _is_ any css.cgroup.
> > 
> > Right - previously the returned task_group would be always associated
> > with a cgroup. Now, it may not be.
> > 
> > The original task_group() should be made accessible for anything that
> > wants a real cgroup in the scheduler hierarchy, and called from the
> > new task_group() function. Not sure what the best naming convention
> > would be, maybe task_group() and effective_task_group() ?
> 
> Right, that doesn't solve the full problem though.
> 
> /proc/sched_debug should show these automagic task_groups, its just that
> there's currently no way to properly name them, we can of course add
> something like a name field to the struct autogroup thing, but what do
> we fill it with? "autogroup-%d" and keep a sequence number for each
> autogroup?

I was considering exactly that for /proc/N/cgroup visibility.  Might get
thumped if I re-use that file though.

quoted text
> Then the below task_group_path() thing can try the autogroup name scheme
> if it finds a NULL css.
> 
> Something like the below might avoid the explosion:
> 
> ---
>  kernel/sched_debug.c |   28 ++++++++++++++--------------
>  1 files changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
> index 2e1b0d1..9b5560f 100644
> --- a/kernel/sched_debug.c
> +++ b/kernel/sched_debug.c
> @@ -87,6 +87,19 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu,
>  }
>  #endif
>  
> +#if defined(CONFIG_CGROUP_SCHED) && \
> +	(defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
> +static void task_group_path(struct task_group *tg, char *buf, int buflen)
> +{
> +	/* may be NULL if the underlying cgroup isn't fully-created yet */
> +	if (!tg->css.cgroup) {
> +		buf[0] = '__PLACEHOLDER__1_';
> +		return;
> +	}
> +	cgroup_path(tg->css.cgroup, buf, buflen);
> +}
> +#endif
> +
>  static void
>  print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
>  {
> @@ -115,7 +128,7 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
>  		char path[64];
>  
>  		rcu_read_lock();
> -		cgroup_path(task_group(p)->css.cgroup, path, sizeof(path));
> +		task_group_path(task_group(p), path, sizeof(path));
>  		rcu_read_unlock();
>  		SEQ_printf(m, " %s", path);
>  	}
> @@ -147,19 +160,6 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
>  	read_unlock_irqrestore(&tasklist_lock, flags);
>  }
>  
> -#if defined(CONFIG_CGROUP_SCHED) && \
> -	(defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
> -static void task_group_path(struct task_group *tg, char *buf, int buflen)
> -{
> -	/* may be NULL if the underlying cgroup isn't fully-created yet */
> -	if (!tg->css.cgroup) {
> -		buf[0] = '__PLACEHOLDER__1_';
> -		return;
> -	}
> -	cgroup_path(tg->css.cgroup, buf, buflen);
> -}
> -#endif
> -
>  void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
>  {
>  	s64 MIN_vruntime = -1, min_vruntime, max_vruntime = -1,
> 


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