linux-kernel - Re: [PATCH v2] selftests/ftrace: Add test to exercize function tracer across cpu hotplug

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Date:   Wed, 13 Dec 2023 21:54:50 +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 v2] selftests/ftrace: Add test to exercize function
 tracer across cpu hotplug

On Wed, 13 Dec 2023 17:08:02 +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").
> 

Looks good to me.

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

Thank you,

> Signed-off-by: Naveen N Rao <naveen@...nel.org>
> ---
> v2: Add a check for next available online cpu, as suggested by Masami.
> 
>  .../ftrace/test.d/ftrace/func_hotplug.tc      | 42 +++++++++++++++++++
>  1 file changed, 42 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..ccfbfde3d942
> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
> @@ -0,0 +1,42 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +# 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 cannot test cpu hotplug in UP environment"
> +  exit_unresolved
> +fi
> +
> +# Find online cpu
> +for i in /sys/devices/system/cpu/cpu[1-9]*; do
> +	if [ -f $i/online ] && [ "$(cat $i/online)" = "1" ]; then
> +		cpu=$i
> +		break
> +	fi
> +done
> +
> +if [ -z "$cpu" ]; then
> +	echo "We cannot test cpu hotplug with a single cpu online"
> +	exit_unresolved
> +fi
> +
> +echo 0 > tracing_on
> +echo > trace
> +
> +: "Set $(basename $cpu) offline/online with function tracer enabled"
> +echo function > current_tracer
> +echo 1 > tracing_on
> +(echo 0 > $cpu/online)
> +(echo "forked"; sleep 1)
> +(echo 1 > $cpu/online)
> +echo 0 > tracing_on
> +echo nop > current_tracer
> 
> base-commit: b85ea95d086471afb4ad062012a4d73cd328fa86
> -- 
> 2.43.0
> 


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