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

[Andrea Cervesato]

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>