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Date: Tue, 3 Sep 2013 21:12:07 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>, Jiri Olsa <jolsa@redhat.com>
Subject: Re: [RFC][PATCH 01/18 v2] ftrace: Add hash list to save RCU unsafe
 functions
Message-ID: <20130904041207.GO3871@linux.vnet.ibm.com>
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On Tue, Sep 03, 2013 at 10:01:15PM -0400, Steven Rostedt wrote:
> On Tue, 3 Sep 2013 18:24:04 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> 
> 
> > >  static DEFINE_PER_CPU(unsigned long, ftrace_rcu_func);
> > > @@ -588,15 +593,14 @@ static void
> > >  ftrace_unsafe_callback(unsigned long ip, unsigned long parent_ip,
> > >  		       struct ftrace_ops *op, struct pt_regs *pt_regs)
> > >  {
> > > -	int bit;
> > > -
> > > +	/* Make sure we see disabled or not first */
> > > +	smp_rmb();
> > 
> > 	smp_mb__before_atomic_inc()?
> > 
> 
> Ah, but this is before an atomic_read(), and not an atomic_inc(), thus
> the normal smp_rmb() is still required.

Good point, color me blind, dazed, and confused.

							Thanx, Paul

> -- Steve
> 
> > >  	if (atomic_read(&ftrace_unsafe_rcu_disabled))
> > >  		return;
> > > 
> > >  	preempt_disable_notrace();
> > > 
>