linux-kernel - Re: [PATCH] tracing/kprobes: 'nmissed' not showed correctly for kretprobe

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Date:   Wed, 5 Jan 2022 14:22:08 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Xiangyang Zhang <xyz.sun.ok@...il.com>
Cc:     mingo@...hat.com, Masami Hiramatsu <mhiramat@...nel.org>,
        oleg@...hat.com, namhyung.kim@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/kprobes: 'nmissed' not showed correctly for
 kretprobe

Resending again, this time with Masami's working email address.

On Wed, 5 Jan 2022 14:15:56 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Sat, 11 Dec 2021 23:00:32 +0800
> Xiangyang Zhang <xyz.sun.ok@...il.com> wrote:
> 
> > The 'nmissed' column of the 'kprobe_profile' file for kretprobe is
> > always zero, because 'nmissed' for kretprobe is maintained in
> > 'tk->rp.nmissed' but not in 'tk->rp.kp.nmissed'
> > 
> > Fixes: c31ffb3ff633 ("tracing/kprobes: Factor out struct trace_probe")
> > Signed-off-by: Xiangyang Zhang <xyz.sun.ok@...il.com>
> > ---
> >  kernel/trace/trace_kprobe.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index d10c01948e68..2b9de6826e94 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -1175,15 +1175,17 @@ static int probes_profile_seq_show(struct seq_file *m, void *v)
> >  {
> >  	struct dyn_event *ev = v;
> >  	struct trace_kprobe *tk;
> > +	unsigned long nmissed = 0;  
> 
> No need to initialize this to zero, the first use is an assignment.
> 
> >  
> >  	if (!is_trace_kprobe(ev))
> >  		return 0;
> >  
> >  	tk = to_trace_kprobe(ev);
> > +	nmissed = tk->rp.handler ? tk->rp.nmissed : tk->rp.kp.nmissed;
> >  	seq_printf(m, "  %-44s %15lu %15lu\n",
> >  		   trace_probe_name(&tk->tp),
> >  		   trace_kprobe_nhit(tk),
> > -		   tk->rp.kp.nmissed);
> > +		   nmissed);  
> 
> Masami, what's your thoughts on this patch?
> 
> -- Steve
> 
> >  
> >  	return 0;
> >  }  
>