On 01/09, Srivatsa Vaddagiri wrote:
>
> On Mon, Jan 08, 2007 at 08:06:35PM +0300, Oleg Nesterov wrote:
> > Ah, missed you point, thanks. Yet another old problem which was not introduced
> > by recent changes. And yet another indication we should avoid kthread_stop()
> > on CPU_DEAD event :) I believe this is easy to fix, but need to think more.
>
> I think the problem is not just with CPU_DEAD. Anyone who calls
> cleanup_workqueue_thread (say destroy_workqueue?) will see this race.
destroy_workqueue() first does flush_workqueue(), so it should be ok.
Anyway I agree with you, we shouldn't clear cwq->thread until it exits,
> Do you see any problems if cleanup_workqueue_thread is changed as:
>
> cleanup_workqueue_thread()
> {
> kthread_stop(p);
> spin_lock(cwq->lock);
> cwq->thread = NULL;
> spin_unlock(cwq->lock);
> }
I think the same. In fact I suspect we even don't need spin_lock, but didn't
have a time to read the code since our discussion.
Oleg.
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