linux-kernel - Re: [PATCH 3/8] ftrace: Add enable/disable ftrace

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Date:	Tue, 24 Jan 2012 02:26:42 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, mingo@...hat.com, paulus@...ba.org,
	acme@...stprotocols.net, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, aarapov@...hat.com
Subject: Re: [PATCH 3/8] ftrace: Add enable/disable ftrace_ops control
 interface

On Wed, Dec 21, 2011 at 11:01:33AM -0500, Steven Rostedt wrote:
> On Wed, 2011-12-21 at 12:48 +0100, Jiri Olsa wrote:
> > +static int control_ops_is_disabled(struct ftrace_ops *ops)
> > +{
> > +	atomic_t *disabled = this_cpu_ptr(ops->disabled);
> 
> Again, the use of "this_cpu_ptr" is wrong. Gah! We should nuke all of
> that crap.
> 

Is it? It includes the preemption check if CONFIG_DEBUG_PREEMPT, just
like __get_cpu_var()

Just saying that because in a later version of this patch, Jiri used
per_cpu_ptr(ops->disabled, cpu). And this is the wrong thing to do
given that we always fetch the local pointer and per_cpu_ptr() doesn't
check for preemption disabled.

 
> > +	return atomic_read(disabled);
> > +}

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