linux-kernel - Re: [RFC][PATCH 01/18 v2] ftrace: Add hash list to save RCU unsafe functions

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Date:	Tue, 3 Sep 2013 22:01:15 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [RFC][PATCH 01/18 v2] ftrace: Add hash list to save RCU unsafe
 functions

On Tue, 3 Sep 2013 18:24:04 -0700
"Paul E. McKenney" <paulmck@...ux.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.

-- Steve

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