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Subject: Re: [PATCH,RFC] perf: panic due to inclied cpu context task_ctx
 value
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>, Paul Mackerras <paulus@samba.org>,
        Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
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Date: Wed, 30 Mar 2011 17:40:52 +0200
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On Wed, 2011-03-30 at 17:32 +0200, Oleg Nesterov wrote:
> > +#ifdef HAVE_JUMP_LABEL
> > +static inline
> > +void perf_sched_events_inc(void)
> > +{
> > +     jump_label_inc(&perf_sched_events_out);
> > +     smp_mb__after_atomic_inc();
> > +     jump_label_inc(&perf_sched_events_in);
> > +}
> > +
> > +static inline
> > +void perf_sched_events_dec(void)
> > +{
> > +     if (atomic_dec_and_test(&perf_sched_events_in)) {
> > +             jump_label_disable(&perf_sched_events_in);
> > +             synchronize_sched();
> > +     }
> > +
> > +     jump_label_dec(&perf_sched_events_out);
> 
> probably smp_mb__after_atomic_inc() needs a comment...

You don't need it, jump_label_inc() uses atomic_add_return() which
implies a full mb.