[LTP] [PATCH v2 12/13] hotplug/cpu_hotplug: Repopulate cgroup:cpusets after testing hotplug

[Cyril Hrubis <chrubis@suse.cz>]

Hi!
> LTP tests that online CPUs must test for the legacy cgroup hierarchy and
> update the cpusets for all users/sessions. Add this code the
> cpu_online() helper.

I'm not sure if we want to work around kernel/systemd bugs like this,
but even if we do we probably want to inform user about the bug.  Maybe
we should just check if the cpus are disabled after the test, if so,
restore them and fail the test.

> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
> ---
>  .../cpu_hotplug/include/cpuhotplug_hotplug.sh      | 36 ++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/testcases/kernel/hotplug/cpu_hotplug/include/cpuhotplug_hotplug.sh b/testcases/kernel/hotplug/cpu_hotplug/include/cpuhotplug_hotplug.sh
> index 9f856e554..35ec7c86b 100644
> --- a/testcases/kernel/hotplug/cpu_hotplug/include/cpuhotplug_hotplug.sh
> +++ b/testcases/kernel/hotplug/cpu_hotplug/include/cpuhotplug_hotplug.sh
> @@ -58,6 +58,39 @@ set_affinity()
>      return $?
>  }
>  
> +# repopulate_cpusets()
> +#
> +# If the legacy cgroup hierarchy is in use, and cpuset is mounted, copy
> +# the permitted cpus from the root group, which always has all available
> +# cpus and memory, into the other hierarchy nodes. This prevents hotplug
> +# tests from losing CPUs, and affecting the results of later tests.
> +#
> +CPUSET="/sys/fs/cgroup/cpuset"
> +repopulate_cpusets()
> +{
> +	# Only if we have cpusets
> +	if [ ! -d ${CPUSET} ] ; then
> +		return;
> +	fi
> +
> +	# And then only legacy cpusets
> +	if grep --quiet "/sys/fs/cgroup/cpuset[ ]*cgroup2" /proc/mounts ; then
> +		return;
> +	fi
> +
> +	# Copy root cpus into system and user slices
> +	cat ${CPUSET}/cpuset.cpus > ${CPUSET}/system.slice/cpuset.cpus
> +	cat ${CPUSET}/cpuset.cpus > ${CPUSET}/user.slice/cpuset.cpus

This will fail on distros that do not use systemd, we should check first
if system.slice and user.slice directories are present.

> +	# Fix each session of each user
> +	for TUSER in ${CPUSET}/user.slice/user-*.slice ; do
> +		cat ${CPUSET}/cpuset.cpus > ${TUSER}/cpuset.cpus
> +		for SESSION in ${TUSER}/session-*.scope; do
> +			cat ${CPUSET}/cpuset.cpus > ${SESSION}/cpuset.cpus
> +		done
> +	done
> +
> +}
> +
>  # online_cpu(CPU)
>  #
>  #  Onlines the given CPU.  Returns a true value if it was able
> @@ -77,6 +110,9 @@ online_cpu()
>  
>      $TIME echo 1 > /sys/devices/system/cpu/cpu${CPU}/online
>      RC=$?
> +
> +    repopulate_cpusets
> +
>      report_timing "Online cpu ${CPU}"
>      return $RC
>  }
> -- 
> 2.14.2
> 

-- 
Cyril Hrubis
chrubis@suse.cz