linux-kernel - Re: [PATCH] selftests/ftrace: Add test to exercize function tracer across cpu hotplug

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Date:   Wed, 13 Dec 2023 09:40:38 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Naveen N Rao <naveen@...nel.org>
Cc:     <linux-kselftest@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] selftests/ftrace: Add test to exercize function tracer
 across cpu hotplug

Hi Naveen,

On Tue, 12 Dec 2023 14:26:07 +0530
Naveen N Rao <naveen@...nel.org> wrote:

> Add a test to exercize cpu hotplug with the function tracer active to
> ensure that sensitive functions in idle path are excluded from being
> traced. This helps catch issues such as the one fixed by commit
> 4b3338aaa74d ("powerpc/ftrace: Fix stack teardown in ftrace_no_trace").
> 
> Signed-off-by: Naveen N Rao <naveen@...nel.org>
> ---
>  .../ftrace/test.d/ftrace/func_hotplug.tc      | 30 +++++++++++++++++++
>  1 file changed, 30 insertions(+)
>  create mode 100644 tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> new file mode 100644
> index 000000000000..49731a2b5c23
> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> @@ -0,0 +1,30 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +# description: ftrace - function trace across cpu hotplug
> +# requires: function:tracer
> +
> +if ! which nproc ; then
> +  nproc() {
> +    ls -d /sys/devices/system/cpu/cpu[0-9]* | wc -l
> +  }
> +fi
> +
> +NP=`nproc`
> +
> +if [ $NP -eq 1 ] ;then
> +  echo "We can not test cpu hotplug in UP environment"
> +  exit_unresolved
> +fi

This looks good, but can you find the 2nd online CPU before
this test?
I mean, there is a case that cpu1 is already offlined and others
like cpu2 is onlined. So we need to use the 2nd online cpu.

Thank you,

> +
> +echo 0 > tracing_on
> +echo > trace
> +: "Set CPU1 offline/online with function tracer enabled"
> +echo function > current_tracer
> +echo 1 > tracing_on
> +(echo 0 > /sys/devices/system/cpu/cpu1/online)
> +(echo "forked"; sleep 1)
> +(echo 1 > /sys/devices/system/cpu/cpu1/online)
> +echo 0 > tracing_on
> +
> +: "Check CPU1 events are recorded"
> +grep -q -e "\[001\]" trace
> 
> base-commit: b85ea95d086471afb4ad062012a4d73cd328fa86
> -- 
> 2.43.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>