* Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > On 09/01, Ingo Molnar wrote: > > > > In fact i dont see any proper serialization here: there appears to > > be a race between the initial task and the init task (which are not > > one and the same). The race is possibly timing dependent as well, > > hence the (in hindsight, false) dependency on the stackprotector > > commit. > > Yes, this looks racy, and I think this was always racy. > > > I think the bug was introduced > > via: > > > > cdd140b: kthreads: simplify the startup synchronization > > Cough ;) No, I don't think this patch introduced this bug. With or > without this patch, kthread_create() assumes kthreadd_task != > NULL, otherwise wake_up_process(kthreadd_task) is obviously can > crash. yeah - was just a guess. > > static DEFINE_SPINLOCK(kthread_create_lock); > > static LIST_HEAD(kthread_create_list); > > + > > struct task_struct *kthreadd_task; > > +DECLARE_COMPLETION(kthreadd_task_init_done); > > > > struct kthread_create_info > > { > > @@ -129,6 +131,9 @@ struct task_struct *kthread_create(int (*threadfn)(void *data), > > list_add_tail(&create.list, &kthread_create_list); > > spin_unlock(&kthread_create_lock); > > > > + if (unlikely(!kthreadd_task)) > > + wait_for_completion(&kthreadd_task_init_done); > > + > > Yes, this should work. But I _think_ we can make the better fix... > > I'll try to make the patch soon. Afaics we don't need > kthreadd_task_init_done. ok. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html