Re: [PATCH v3] selftests: cpufreq: stop CPU hotplug loop after cpufreq update test

[Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>]

On 10/30/2026 6:42 PM, xiong yining wrote:
> Original test uses a fixed 5000 iteration loop to trigger CPU hotplug
> for verifying cpufreq synchronization between CPU hotplug and sysfs
> writes.
> 
> Two issues exist:
> 1. Background hotplug task keeps running after test completes, causing
> redundant CPU on/offline operations.
> 2. When cpufreq frequency setup is slow, the hotplug loop may exit
> before frequency updates finish, which breaks test purpose.
> 
> Use signal notification to terminate the infinite hotplug loop, and
> add an EXIT trap to clean up the hotplug child when this test function
> terminates abnormally.
> 
> This makes hotplug run only during cpufreq sysfs write test,
> align with test objective.
> 
> Signed-off-by: xiong yining <xiongyining1480@phytium.com.cn>

Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>

> ---
> Changes in v3:
> - Start the hotplug child after governor switch and sysfs frequency reads,
> to avoid -EBUSY errors when the target CPU is offline.
> 
> Changes in v2:
> - Stop the hotplug child process by signal notification instead of
> a stop file, avoiding the predictable temporary path.
> - Add an exit trap so the hotplug child is also cleaned up when the
> main shell terminates abnormally.
> - Link to v1:
> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2662696.html
> 
> This addresses the security and robustness concerns raised by Sashiko.
> ---
>   .../selftests/cpufreq/special-tests.sh        | 30 +++++++++++++++----
>   1 file changed, 24 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/cpufreq/special-tests.sh b/tools/testing/selftests/cpufreq/special-tests.sh
> index e87ed7c8e5e5..0665da8f2444 100755
> --- a/tools/testing/selftests/cpufreq/special-tests.sh
> +++ b/tools/testing/selftests/cpufreq/special-tests.sh
> @@ -16,6 +16,8 @@ source cpu.sh
>   source cpufreq.sh
>   source governor.sh
>   
> +HOTPLUG_PID=""
> +
>   # Test 1
>   # $1: policy
>   __simple_lockdep()
> @@ -92,6 +94,16 @@ governor_race()
>   	restore_all_governors
>   }
>   
> +hotplug_cleanup()
> +{
> +	if [[ -n "$HOTPLUG_PID" ]]; then
> +		kill -s SIGTERM "$HOTPLUG_PID"
> +		wait "$HOTPLUG_PID"
> +
> +		HOTPLUG_PID=""
> +	fi
> +}
> +
>   # Test 4
>   # $1: cpu
>   hotplug_with_updates_cpu()
> @@ -101,14 +113,18 @@ hotplug_with_updates_cpu()
>   	# switch to ondemand
>   	__switch_governor_for_cpu $1 "ondemand"
>   
> -	for i in `seq 1 5000`
> -	do
> -		reboot_cpu $1
> -	done &
> -
>   	local freqs=$(cat $filepath/scaling_available_frequencies)
>   	local oldfreq=$(cat $filepath/scaling_min_freq)
>   
> +	(
> +		local quit=0
> +		trap 'quit=1' SIGTERM
> +		while [ "$quit" -eq 0 ]; do
> +			reboot_cpu "$1"
> +		done
> +	) &
> +	HOTPLUG_PID=$!
> +
>   	for j in `seq 1 5000`
>   	do
>   		# Set all frequencies one-by-one
> @@ -117,14 +133,16 @@ hotplug_with_updates_cpu()
>   		done
>   	done
>   
> +	hotplug_cleanup
> +
>   	# restore old freq
>   	echo $oldfreq > $filepath/scaling_min_freq
>   }
>   
>   hotplug_with_updates()
>   {
> +	trap 'hotplug_cleanup' EXIT
>   	save_all_governors
>   	for_each_non_boot_cpu hotplug_with_updates_cpu
> -	wait
>   	restore_all_governors
>   }


-- 
Thx and BRs,
Zhongqiu Han