Messages in this thread | | | Date | Tue, 1 Sep 2009 15:04:36 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] kthreads: Fix startup synchronization boot crash |
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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.
> 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.
Oleg.
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