Sorry for delay, just noticed this thread... On 07/27, NeilBrown wrote: > > The race as I understand it is with this code: > > > list_replace_rcu(&leader->tasks, &tsk->tasks); > list_replace_init(&leader->sibling, &tsk->sibling); > > tsk->group_leader = tsk; > leader->group_leader = tsk; > > > which seems to be called with only tasklist_lock held, which doesn't seem to > be held in the cgroup code. > > If the "thread_group_leader(leader)" call in cgroup_attach_proc() runs before > this chunk is run with the same value for 'leader', but the > while_each_thread is run after, then the while_read_thread() might loop > forever. rcu_read_lock doesn't prevent this from happening. Yes. This was already discussed. See http://marc.info/?t=127688987300002 Damn. I forgot about this completely. > The code in de_thread() is actually questionable by itself. > "list_replace_rcu" cannot really be used on the head of a list - it is only > meant to be used on a member of a list. > To move a list from one head to another you should be using > list_splice_init_rcu(). Hmm... can't understand this part. And just in case... list_replace_rcu() looks fine afaics. The real problem is release_task(old_leader) which does list_del_rcu(old_leader->thread_group), this is what breaks while_each_thread(). > The ->tasks list doesn't seem to have a clearly distinguished 'head' Exactly. This is the problem. But: you seem to confused ->tasks and ->thread_group ;) Oleg. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
