Messages in this thread | | | Date | Thu, 6 Jan 2022 07:32:03 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] tracing/kprobes: 'nmissed' not showed correctly for kretprobe |
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On Wed, 5 Jan 2022 14:22:08 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:
> Resending again, this time with Masami's working email address. > > On Wed, 5 Jan 2022 14:15:56 -0500 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > On Sat, 11 Dec 2021 23:00:32 +0800 > > Xiangyang Zhang <xyz.sun.ok@gmail.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@gmail.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?
OK, this is a good catch :), but there are 2 issues.
1. kretprobe can be skipped by 2 reasons, shortage of kretprobe_instance which is counted by rp.nmissed, and kprobe itself is missed by some reason (this can be happen if KPROBE_EVENTS_ON_NOTRACE=n. Thus, better solution is to show 'tk->rp.nmissed + tk->rp.kp.nmissed'.
2. the commit c31ffb3ff633 is not actual commit which introduce this issue. this was introduced by 4a846b443b4e ("tracing/kprobes: Cleanup kprobe tracer code.")
'git blame' tells you the commit which changes that line, but that can be just a refactoring (renaming). I recommend you to search the correct one by 'git log -p'.
Thank you,
> > > > -- Steve > > > > > > > > return 0; > > > } > > >
-- Masami Hiramatsu <mhiramat@kernel.org>
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