linux-kernel - Re: [PATCH v7 01/10] tracing: Add support for SOFT

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Date:	Tue, 27 Aug 2013 18:29:06 -0500
From:	Tom Zanussi <tom.zanussi@...ux.intel.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	masami.hiramatsu.pt@...achi.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 01/10] tracing: Add support for SOFT_DISABLE to
 syscall events

On Tue, 2013-08-27 at 16:01 -0400, Steven Rostedt wrote:
> On Tue, 27 Aug 2013 14:40:13 -0500
> Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:
> 
>   		return;
> > -	if (!test_bit(syscall_nr, tr->enabled_enter_syscalls))
> > +
> > +	/* Here we're inside the tp handler's rcu_read_lock (__DO_TRACE()) */
> > +	ftrace_file = rcu_dereference_raw(tr->enter_syscall_files[syscall_nr]);
> 
> What's the reason for using rcu_dereference_raw() and not normal
> rcu_dereference?
> 

This is because we know the tracepoint handler has rcu_read_lock_held()
and so we don't need to do the rcu_dereference_check().

Tom

> -- Steve
> 
> > +	if (!ftrace_file)
> > +		return;
> > +
> > +	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
> >  		return;
> >  


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