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Subject: Re: [PATCH 1/2] perf_events: add cgroup support (v8)
From: Peter Zijlstra <peterz@infradead.org>
To: eranian@google.com
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, paulus@samba.org,
        davem@davemloft.net, fweisbec@gmail.com, perfmon2-devel@lists.sf.net,
        eranian@gmail.com, robert.richter@amd.com, acme@redhat.com,
        lizf@cn.fujitsu.com, Paul Menage <menage@google.com>
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Date: Thu, 20 Jan 2011 15:39:05 +0100
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On Thu, 2011-01-20 at 15:30 +0200, Stephane Eranian wrote:
> @@ -4259,8 +4261,20 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
>  
>         /* Reassign the task to the init_css_set. */
>         task_lock(tsk);
> +       /*
> +        * we mask interrupts to prevent:
> +        * - timer tick to cause event rotation which
> +        *   could schedule back in cgroup events after
> +        *   they were switched out by perf_cgroup_sched_out()
> +        *
> +        * - preemption which could schedule back in cgroup events
> +        */
> +       local_irq_save(flags);
> +       perf_cgroup_sched_out(tsk);
>         cg = tsk->cgroups;
>         tsk->cgroups = &init_css_set;
> +       perf_cgroup_sched_in(tsk);
> +       local_irq_restore(flags);
>         task_unlock(tsk);
>         if (cg)
>                 put_css_set_taskexit(cg); 

So you too need a callback on cgroup change there.. Li, Paul, any chance
we can fix this cgroup_subsys::exit callback? The scheduler code needs
to do funny thing because its in the wrong place as well.