linux-kernel - Re: [PATCH] selftests/ftrace: Stop tracing before searching non-exist event entry

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Message-ID: <20211013181630.13a4848a@gandalf.local.home>
Date:   Wed, 13 Oct 2021 18:16:30 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/ftrace: Stop tracing before searching
 non-exist event entry

On Tue, 28 Sep 2021 09:11:06 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

I'm finally getting through my queue to see this.

> Stop tracing before searching the pattern which is expected to
> not exist on the trace buffer. In some case, it will take too
> long and may not come back eternally because while searching
> the tracing data will be increased by the searching activity.
> 
> I found this with enabling kernel debug options, like kmemleak,
> lockdep etc. and run it on qemu with 2 CPUs. It did not come
> back in 20 minutes and finally I need to interrupt it to stop.

One other option is to bring back the old behavior:

  echo 1 > options/pause-on-trace

Which will stop tracing as the trace file is read.

But either way works for me.

-- Steve

> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  .../ftrace/test.d/ftrace/func_profiler.tc          |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func_profiler.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func_profiler.tc
> index 1dbd766c0cd2..440f4d87aa4b 100644
> --- a/tools/testing/selftests/ftrace/test.d/ftrace/func_profiler.tc
> +++ b/tools/testing/selftests/ftrace/test.d/ftrace/func_profiler.tc
> @@ -56,6 +56,9 @@ clear_trace
>  sleep 1
>  
>  echo "make sure something other than scheduler is being traced"
> +
> +echo 0 > tracing_on
> +
>  if ! grep -v -e '^#' -e 'schedule' trace > /dev/null; then
>  	cat trace
>  	fail "no other functions besides schedule was found"