Re: [RFC PATCH tip/master 1/3] trace: kprobes: Show sum of probe/retprobe nmissed count

[Alban Crequy]

On Wed, Mar 29, 2017 at 7:22 AM, Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> Show sum of probe and retprobe nmissed count in
> kprobe_profile, since retprobe can be missed even
> if the kprobe itself succeeeded.
> This explains user why their return probe didn't hit
> sometimes.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

I tested this patch with my kretprobe on "inet_csk_accept" when there
are many processes waiting in the accept() syscall. I can now
successfully see the nmissed counter in
/sys/kernel/debug/tracing/kprobe_profile being incremented when the
kretprobe is missed.

Tested-by: Alban Crequy <alban@xxxxxxxxxx>


> ---
>  kernel/trace/trace_kprobe.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 013f4e7..bbdc3de 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -896,7 +896,7 @@ static int probes_profile_seq_show(struct seq_file *m, void *v)
>         seq_printf(m, "  %-44s %15lu %15lu\n",
>                    trace_event_name(&tk->tp.call),
>                    trace_kprobe_nhit(tk),
> -                  tk->rp.kp.nmissed);
> +                  tk->rp.kp.nmissed + tk->rp.nmissed);
>
>         return 0;
>  }
>