From ace783b9bbfa2182b4a561498db3f09a0c56bc79 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Thu, 24 Jan 2013 14:30:48 +0800 Subject: sched: split out css_online/css_offline from tg creation/destruction This is a preparaton for later patches. - What do we gain from cpu_cgroup_css_online(): After ss->css_alloc() and before ss->css_online(), there's a small window that tg->css.cgroup is NULL. With this change, tg won't be seen before ss->css_online(), where it's added to the global list, so we're guaranteed we'll never see NULL tg->css.cgroup. - What do we gain from cpu_cgroup_css_offline(): tg is freed via RCU, so is cgroup. Without this change, This is how synchronization works: cgroup_rmdir() no ss->css_offline() diput() syncornize_rcu() ss->css_free() <-- unregister tg, and free it via call_rcu() kfree_rcu(cgroup) <-- wait possible refs to cgroup, and free cgroup We can't just kfree(cgroup), because tg might access tg->css.cgroup. With this change: cgroup_rmdir() ss->css_offline() <-- unregister tg diput() synchronize_rcu() <-- wait possible refs to tg and cgroup ss->css_free() <-- free tg kfree_rcu(cgroup) <-- free cgroup As you see, kfree_rcu() is redundant now. Signed-off-by: Li Zefan Signed-off-by: Tejun Heo Acked-by: Ingo Molnar --- include/linux/sched.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/linux/sched.h') diff --git a/include/linux/sched.h b/include/linux/sched.h index 206bb089c06..577eb973de7 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2750,7 +2750,10 @@ extern void normalize_rt_tasks(void); extern struct task_group root_task_group; extern struct task_group *sched_create_group(struct task_group *parent); +extern void sched_online_group(struct task_group *tg, + struct task_group *parent); extern void sched_destroy_group(struct task_group *tg); +extern void sched_offline_group(struct task_group *tg); extern void sched_move_task(struct task_struct *tsk); #ifdef CONFIG_FAIR_GROUP_SCHED extern int sched_group_set_shares(struct task_group *tg, unsigned long shares); -- cgit v1.2.3