Hi, In memcg, we use the cgroup_lock basically to synchronize against two events: attaching tasks and children to a cgroup. For the problem of attaching tasks, I am using something similar to cpusets: when task attaching starts, we will flip a flag "attach_in_progress", that will be flipped down when it finishes. This way, all readers can know that a task is joining the group and take action accordingly. With this, we can guarantee that the behavior of move_charge_at_immigrate continues safe Protecting against children creation requires a bit more work. For those, the calls to cgroup_lock() all live in handlers like mem_cgroup_hierarchy_write(), where we change a tunable in the group, that is hierarchy-related. For instance, the use_hierarchy flag cannot be changed if the cgroup already have children. Furthermore, those values are propageted from the parent to the child when a new child is created. So if we don't lock like this, we can end up with the following situation: A B memcg_css_alloc() mem_cgroup_hierarchy_write() copy use hierarchy from parent change use hierarchy in parent finish creation. This is mainly because during create, we are still not fully connected to the css tree. So all iterators and the such that we could use, will fail to show that the group has children. My observation is that all of creation can proceed in parallel with those tasks, except value assignment. So what this patchseries does is to first move all value assignment that is dependent on parent values from css_alloc to css_online, where the iterators all work, and then we lock only the value assignment. This will guarantee that parent and children always have consistent values. Glauber Costa (4): cgroup: warn about broken hierarchies only after css_online memcg: prevent changes to move_charge_at_immigrate during task attach memcg: split part of memcg creation to css_online memcg: replace cgroup_lock with memcg specific memcg_lock kernel/cgroup.c | 18 +++---- mm/memcontrol.c | 164 +++++++++++++++++++++++++++++++++++++++++--------------- 2 files changed, 129 insertions(+), 53 deletions(-) -- 1.7.11.7 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>