linux-kernel - Re: [PATCH v2 1/2] tracing/kprobes: add a helper method to return number of probe hits

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Date:   Mon, 12 Dec 2016 17:53:08 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Marcin Nowakowski <marcin.nowakowski@...tec.com>,
        Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] tracing/kprobes: add a helper method to return
 number of probe hits

Masami,

I just noticed that you were not Cc'd. Can you give your ack on this
and the other patch. I'll bounce both of them to you.

Thanks!

-- Steve


On Fri, 9 Dec 2016 15:19:37 +0100
Marcin Nowakowski <marcin.nowakowski@...tec.com> wrote:

> The number of probe hits is stored in a percpu variable and therefore
> can't be read directly. Add a helper method trace_kprobe_nhit() that
> performs the required calculation.
> 
> It will be used in a follow-up commit that changes kprobe selftests to
> verify the number of probe hits.
> 
> Signed-off-by: Marcin Nowakowski <marcin.nowakowski@...tec.com>
> ---
>  kernel/trace/trace_kprobe.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
>  v2: improved commit message as suggested by Steven Rostedt
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index eb6c9f1..a2af1bc 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -73,6 +73,17 @@ static nokprobe_inline bool trace_kprobe_is_on_module(struct trace_kprobe *tk)
>  	return !!strchr(trace_kprobe_symbol(tk), ':');
>  }
>  
> +static nokprobe_inline unsigned long trace_kprobe_nhit(struct trace_kprobe *tk)
> +{
> +	unsigned long nhit = 0;
> +	int cpu;
> +
> +	for_each_possible_cpu(cpu)
> +		nhit += *per_cpu_ptr(tk->nhit, cpu);
> +
> +	return nhit;
> +}
> +
>  static int register_kprobe_event(struct trace_kprobe *tk);
>  static int unregister_kprobe_event(struct trace_kprobe *tk);
>  
> @@ -882,14 +893,10 @@ static const struct file_operations kprobe_events_ops = {
>  static int probes_profile_seq_show(struct seq_file *m, void *v)
>  {
>  	struct trace_kprobe *tk = v;
> -	unsigned long nhit = 0;
> -	int cpu;
> -
> -	for_each_possible_cpu(cpu)
> -		nhit += *per_cpu_ptr(tk->nhit, cpu);
>  
>  	seq_printf(m, "  %-44s %15lu %15lu\n",
> -		   trace_event_name(&tk->tp.call), nhit,
> +		   trace_event_name(&tk->tp.call),
> +		   trace_kprobe_nhit(tk),
>  		   tk->rp.kp.nmissed);
>  
>  	return 0;