On 10/16, Tejun Heo wrote: > > cgroup_subsys->fork() is invoked way before the new task is added to > the css_set. Plus, it called before this task (and even its task_struct) was fully initialized. All I can say is: personally I like this patch, it also simplifies copy_process(). But I am in no position to ack it. I seem to forget everything (not too much ;) I ever knew about this code. A couple of off-topic questions. With or without this patch I do not understand cgroup_fork, /* * We don't need to task_lock() current because current->cgroups * can't be changed concurrently here. The parent obviously hasn't * exited and called cgroup_exit(), and we are synchronized against * cgroup migration through threadgroup_change_begin(). */ child->cgroups = current->cgroups; get_css_set(child->cgroups); How so? threadgroup_change_begin() is only called if CLONE_THREAD. So in theory this copy + atomic_add looks racy... And it seems that fork() can race with cgroup iterator. post_fork will notice use_task_css_set_links, but until then the child belongs to the parent's css and it is not "visible" to iterator (and right after cgroup_fork() it is not visible to do_each_thread() if use_task_css_set_links is not set). For example. Suppose that the child migrates to another cgroup after copy_process() makes it visible to the user-space. Then update_if_frozen sets CGROUP_FROZEN (again, cgroup_iter_next do not see this child). Now, post_fork calls freezer_fork() and hits BUG_ON(CGROUP_FROZEN). But again, I do not blame this patch. I am starting to think again about a big-rw-lock around copy_process. Recently I tried to add one around dup_mmap for uprobes, but perhaps cgroups can use it too... Oleg. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
