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From: Paul Menage <menage@google.com>
Date: Mon, 15 Nov 2010 17:55:13 -0800
Message-ID: <AANLkTikvcug2V70Uy7oGnO5vFZbS+DLvzP4wpysdU5uV@mail.gmail.com>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>, Valdis.Kletnieks@vt.edu,
        Oleg Nesterov <oleg@redhat.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
        Markus Trippelsdorf <markus@trippelsdorf.de>,
        Daniel Lezcano <daniel.lezcano@free.fr>
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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() ?

Paul