[LTP] [PATCH] cgroup_fj: don't disable controller that was already enabled

[Wei Gao]

On Thu, Jun 11, 2026 at 05:03:41PM +0200, Andrea Cervesato wrote:
> From: Andrea Cervesato <andrea.cervesato@suse.com>
> 
> On immutable distributions (and systemd-managed systems in general)
> the cpuset controller is typically already enabled at the root cgroup
> level. The cleanup tried to unconditionally disable it via
> subtree_control, which failed with EBUSY because other system cgroups
> were still using it, producing a spurious TWARN.
> 
> Save whether the controller was already enabled at root before
> cgroup_require and skip the root-level disable in cleanup when it
> was.
> 
> Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
> ---
>  testcases/kernel/controllers/cgroup_fj/cgroup_fj_common.sh | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/testcases/kernel/controllers/cgroup_fj/cgroup_fj_common.sh b/testcases/kernel/controllers/cgroup_fj/cgroup_fj_common.sh
> index 153d351d7936effb15527620f565acaaed7ac747..8b5e73466ba32d2c66a2805a03f4d2136c16509b 100755
> --- a/testcases/kernel/controllers/cgroup_fj/cgroup_fj_common.sh
> +++ b/testcases/kernel/controllers/cgroup_fj/cgroup_fj_common.sh
> @@ -57,6 +57,14 @@ create_subgroup()
>  
>  common_setup()
>  {
> +    # Check if the controller is already enabled at root before
> +    # cgroup_require potentially enables it, so that cleanup does
> +    # not disable a controller the system was already using.
> +    if [ -f /sys/fs/cgroup/cgroup.subtree_control ] && \
> +       grep -qw "$subsystem" /sys/fs/cgroup/cgroup.subtree_control; then
> +        ctrl_was_enabled=1
> +    fi
> +
>      cgroup_require "$subsystem"
>      mount_point=$(cgroup_get_mountpoint "$subsystem")
>      start_path=$(cgroup_get_test_path "$subsystem")
> @@ -77,7 +85,7 @@ common_cleanup()
>  
>      cgroup_cleanup
>  
> -    if [ "$cgroup_version" = "2" ]; then
> +    if [ "$cgroup_version" = "2" ] && [ "$ctrl_was_enabled" != "1" ]; then
>          case "$subsystem" in
>          cpu|io|memory|pids)
>              :;;
> 
> ---
> base-commit: a375e8deed471723f5a0114c56eb48fe6f6f45d3
> change-id: 20260611-fix_cgroup_immutable-2259f7591f8d
> 
> Best regards,
> -- 
> Andrea Cervesato <andrea.cervesato@suse.com>
Reviewed-by: Wei Gao <wegao@suse.com>
> 
> 
> -- 
> Mailing list info: https://lists.linux.it/listinfo/ltp