linux-kernel - Re: [PATCH 2/4] ftrace/instances: Clear function triggers when removing instances

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Date:   Tue, 16 May 2017 14:33:58 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Shuah Khan <shuah@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 2/4] ftrace/instances: Clear function triggers when
 removing instances

On Tue, 16 May 2017 23:14:23 +0530
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:

> On 2017/05/16 07:31PM, Naveen N. Rao wrote:
> > On 2017/05/15 10:20PM, Steven Rostedt wrote:  
> > > On Sun, 14 May 2017 01:01:02 +0530
> > > "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:
> > >   
> > 
> > [snip]
> >   
> > > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > > > index c4536c449021..3f2aed4ad1ed 100644
> > > > --- a/kernel/trace/trace.c
> > > > +++ b/kernel/trace/trace.c
> > > > @@ -7550,6 +7550,7 @@ static int instance_rmdir(const char *name)
> > > >  	}
> > > >  
> > > >  	tracing_set_nop(tr);
> > > > +	clear_ftrace_function_probes(tr);
> > > >  	event_trace_del_tracer(tr);
> > > >  	ftrace_clear_pids(tr);
> > > >  	ftrace_destroy_function_files(tr);
> > > > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > > > index 291a1bca5748..98e0845f7235 100644
> > > > --- a/kernel/trace/trace.h
> > > > +++ b/kernel/trace/trace.h
> > > > @@ -980,6 +980,7 @@ register_ftrace_function_probe(char *glob, struct trace_array *tr,
> > > >  extern int
> > > >  unregister_ftrace_function_probe_func(char *glob, struct trace_array *tr,
> > > >  				      struct ftrace_probe_ops *ops);
> > > > +extern void clear_ftrace_function_probes(struct trace_array *tr);  
> > > 
> > > This needs to have a stub function when CONFIG_DYNAMIC_FTRACE is not
> > > defined. Otherwise we have:
> > > 
> > > kernel/trace/trace.c:7553:2: error: implicit declaration of function 'clear_ftrace_function_probes' [-Werror=implicit-function-declaration]
> > >   clear_ftrace_function_probes(tr);
> > >   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~  
> 
> The prototype in trace.h is actually guarded by:
> #if defined(CONFIG_FUNCTION_TRACER) && defined(CONFIG_DYNAMIC_FTRACE)
> 
> So, I will guard the call to clear_ftrace_function_probes() in trace.c 
> with the same.
> 

No, the proper thing to do is to make a stub function in the else part
of the #if that the prototype was declared in.

static inline void clear_ftrace_function_probes(struct trace_array *tr)
{
}

Please, lets limit the #ifdef ugliness from the code.

-- Steve