On 01/04, Andrew Morton wrote: > > On Thu, 4 Jan 2007 17:29:36 +0300 > Oleg Nesterov <[EMAIL PROTECTED]> wrote: > > > > In brief: > > > > > > keventd thread hotplug thread > > > -------------- -------------- > > > > > > run_workqueue() > > > | > > > work_fn() > > > | > > > flush_workqueue() > > > | > > > flush_cpu_workqueue > > > | cpu_down() > > > mutex_unlock(wq_mutex); | > > > (above opens window for hotplug) mutex_lock(wq_mutex); > > > | /* bring down cpu */ > > > wait_for_completition(); notifier(CPU_DEAD, ..) > > > | workqueue_cpu_callback > > > | cleanup_workqueue_thread > > > | kthread_stop() > > > | > > > | > > > mutex_lock(wq_mutex); <- Can deadlock > > > > > > > > > The kthread_stop() will wait for keventd() thread to exit, but keventd() > > > is blocked on mutex_lock(wq_mutex) leading to a deadlock. > > This? > > > --- > a/kernel/workqueue.c~flush_workqueue-use-preempt_disable-to-hold-off-cpu-hotplug > +++ a/kernel/workqueue.c > @@ -419,18 +419,22 @@ static void flush_cpu_workqueue(struct c > * Probably keventd trying to flush its own queue. So simply run > * it by hand rather than deadlocking. > */ > - mutex_unlock(&workqueue_mutex); > + preempt_enable();
Ah, (looking at _cpu_down()->stop_machine()), so preempt_disable() not only "pins" the current CPU, it blocks cpu_down(), yes ??? I guess this should work then. I'll try to re-check this code on weekend. 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/
