kselftest/cgroup: fix unexpected testing failure on test_memcontrol

The cgroup testing relies on the root cgroup's subtree_control setting,
If the 'memory' controller isn't set, all test cases will be failed
as following:

$ sudo ./test_memcontrol
not ok 1 test_memcg_subtree_control
not ok 2 test_memcg_current
ok 3 # skip test_memcg_min
not ok 4 test_memcg_low
not ok 5 test_memcg_high
not ok 6 test_memcg_max
not ok 7 test_memcg_oom_events
ok 8 # skip test_memcg_swap_max
not ok 9 test_memcg_sock
not ok 10 test_memcg_oom_group_leaf_events
not ok 11 test_memcg_oom_group_parent_events
not ok 12 test_memcg_oom_group_score_events

To correct this unexpected failure, this patch write the 'memory' to
subtree_control of root to get a right result.

Signed-off-by: Alex Shi <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Jay Kamat <[email protected]>
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Roman Gushchin <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>

0 files changed, 0 insertions, 0 deletions