Re: [PATCH 2/2] selftests/cgroup: Preserve CPU hotplug write errors

[Waiman Long <longman@redhat.com>]

On 8/9/26 4:21 AM, Rui Qi wrote:
> The cpuset partition root state selftest checks several CPU hotplug
> transitions. If writing to a CPU online file fails, the helper still
> runs pause afterwards and returns the status of pause instead of the
> failed write.
>
> This hides the real hotplug failure and can make later checks run
> against expectations for a transition that never happened. Move the
> write before the bookkeeping and return when it fails, so callers can
> observe the hotplug error and the test does not record a CPU as offline
> unless the offline operation actually succeeded.
>
> Fixes: a8c52eba880a ("kselftest/cgroup: Add cpuset v2 partition root state test")
> Signed-off-by: Rui Qi <qirui.001@bytedance.com>

I am aware that on x86-64, cpu0/online may not exist. Other than that, 
under what condition will the write fail as only root is allowed to run 
the script?

Cheers,
Longman

> ---
>   tools/testing/selftests/cgroup/test_cpuset_prs.sh | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index 16c38eb11e63..a2f7208633bc 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -412,6 +412,7 @@ write_cpu_online()
>   	CPU=${1%=*}
>   	VAL=${1#*=}
>   	CPUFILE=//sys/devices/system/cpu/cpu${CPU}/online
> +	echo $VAL > $CPUFILE || return 1
>   	if [[ $VAL -eq 0 ]]
>   	then
>   		OFFLINE_CPUS="$OFFLINE_CPUS $CPU"
> @@ -421,7 +422,6 @@ write_cpu_online()
>   					sort | uniq -u)
>   		}
>   	fi
> -	echo $VAL > $CPUFILE
>   	pause 0.05
>   }
>   
> @@ -493,6 +493,7 @@ set_ctrl_state()
>   			eval $COMM $REDIRECT
>   			;;
>   		    O*) VAL=${CMD#?}
> +			COMM="write_cpu_online $VAL"
>   			write_cpu_online $VAL
>   			;;
>   		    T*) COMM="echo 0 > $TFILE"