linux-kernel - Re: [PATCH] perf/ftrace: fix doubled traces of perf on ftrace:function

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Date:   Fri, 25 Aug 2017 09:56:44 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Zhou Chengming <zhouchengming1@...wei.com>
Cc:     <peterz@...radead.org>, <mingo@...hat.com>,
        <alexander.shishkin@...ux.intel.com>, <acme@...nel.org>,
        <jolsa@...nel.org>, <linux-kernel@...r.kernel.org>,
        <huawei.libin@...wei.com>
Subject: Re: [PATCH] perf/ftrace: fix doubled traces of perf on
 ftrace:function

On Fri, 25 Aug 2017 21:49:37 +0800
Zhou Chengming <zhouchengming1@...wei.com> wrote:

> When run perf on the ftrace:function tracepoint, there is a bug
> which can be reproduced by:
> 
> perf record -e ftrace:function -a sleep 20 &
> perf record -e ftrace:function ls
> perf script
> 
>               ls 10304 [005]   171.853235: ftrace:function:
> perf_output_begin
>               ls 10304 [005]   171.853237: ftrace:function:
> perf_output_begin
>               ls 10304 [005]   171.853239: ftrace:function:
> task_tgid_nr_ns
>               ls 10304 [005]   171.853240: ftrace:function:
> task_tgid_nr_ns
>               ls 10304 [005]   171.853242: ftrace:function:
> __task_pid_nr_ns
>               ls 10304 [005]   171.853244: ftrace:function:
> __task_pid_nr_ns
> 
> We can see that all the function traces are doubled in perf.data
> of "ls".
> 
> The problem is caused by the inconsistency of the register
> function perf_ftrace_event_register() with the probe function
> perf_ftrace_function_call(). The former registers one probe
> for every perf_event. And the latter handles all perf_events
> on the current cpu. So when two perf_events on the current cpu,
> the traces of them will be doubled.
> 
> So this patch adds an extra parameter "event" for perf_tp_event,
> only send sample data to this event when it's not NULL.
> 
> Signed-off-by: Zhou Chengming <zhouchengming1@...wei.com>
> ---
>  include/linux/perf_event.h      |  2 +-
>  include/linux/trace_events.h    |  4 ++--
>  kernel/events/core.c            | 13 +++++++++----
>  kernel/trace/trace_event_perf.c |  4 +++-
>  kernel/trace/trace_kprobe.c     |  4 ++--
>  kernel/trace/trace_syscalls.c   |  4 ++--
>  kernel/trace/trace_uprobe.c     |  2 +-

The trace files look fine to me.

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

>  7 files changed, 20 insertions(+), 13 deletions(-)
>