On 01/07, Srivatsa Vaddagiri wrote: > > On Sun, Jan 07, 2007 at 03:56:03PM +0300, Oleg Nesterov wrote: > > Srivatsa, I'm completely new to cpu-hotplug, so please correct me if I'm > > wrong (in fact I _hope_ I am wrong) but as I see it, the hotplug/workqueue > > interaction is broken by design, it can't be fixed by changing just locking. > > > > Once again. CPU dies, CPU_DEAD calls kthread_stop() and sleeps until > > cwq->thread exits. To do so, this thread must at least complete the > > currently running work->func(). > > If run_workqueue() takes a lock_cpu_hotplug() successfully, then we shouldnt > even reach till this point, as it will block writers (cpu_down/up) until it > completes. > > > run_workqueue() > --------------- > > try_again: > rc = lock_cpu_hotplug_interruptible(); > > if (rc && kthread_should_stop()) > return; > > if (rc != 0) > goto try_again; > > /* cpu_down/up shouldnt happen now untill we call unlock_cpu_hotplug */ > while (!list_empty(..)) > work->func();
This mean that every work->func() which may sleep delays cpu_down/up unpredictable, not good. What about work->func which sleeps then re-queues itself? I guess we can solve this, but this is what I said "other changes". Also, lock_cpu_hotplug() should be per-cpu, otherwise we have livelock. Not that I am against lock_cpu_hotplug (I can't judge), but its usage in run_workqueue looks like complication to me. I may be wrong. But the main problem we don't have it :) Oleg. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/