In validate_change(), there is a check since v2.6.12 to make sure that each of the child cpusets must be a subset of a parent cpuset. IOW, it allows child cpusets to restrict what changes can be made to a parent's "cpuset.cpus". This actually violates one of the core principles of the default hierarchy where a cgroup higher up in the hierarchy should be able to change configuration however it sees fit as deligation breaks down otherwise.
To address this issue, the check is now removed for the default hierarchy to free parent cpusets from being restricted by child cpusets. The check will still apply for legacy hierarchy.
Suggested-by: Tejun Heo tj@kernel.org Signed-off-by: Waiman Long longman@redhat.com --- kernel/cgroup/cpuset.c | 14 +++----------- 1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index d0e163a02099..0dd7d853ed17 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -616,19 +616,11 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial) struct cpuset *c, *par; int ret;
- rcu_read_lock(); - - /* Each of our child cpusets must be a subset of us */ - ret = -EBUSY; - cpuset_for_each_child(c, css, cur) - if (!is_cpuset_subset(c, trial)) - goto out; - - /* Remaining checks don't apply to root cpuset */ - ret = 0; + /* The checks don't apply to root cpuset */ if (cur == &top_cpuset) - goto out; + return 0;
+ rcu_read_lock(); par = parent_cs(cur);
/* On legacy hierarchy, we must be a subset of our parent cpuset. */