On 02/14, Gautham R Shenoy wrote:
>
> This patch reverts all the recent workqueue hacks added to make it
> hotplug safe.
In my opinion these hacks are cleanups :)
Ok. If we use freezer then yes, we can remove cpu_populated_map and just
use for_each_online_cpu(). This is easy and good.
What else you don't like? Why do you want to remove cwq_should_stop() and
restore an ugly (ugly for workqueue.c) kthread_stop/kthread_should_stop() ?
We can restore take_over_works(), although I don't see why this is needed.
But cwq_should_stop() will just work regardless, why do you want to add
this "wait_to_die" ... well, hack :)
> -static DEFINE_MUTEX(workqueue_mutex);
> +static DEFINE_SPINLOCK(workqueue_lock);
No. We can't do this. see below.
> struct workqueue_struct *__create_workqueue(const char *name,
> int singlethread, int freezeable)
> {
> @@ -798,17 +756,20 @@ struct workqueue_struct *__create_workqu
> INIT_LIST_HEAD(&wq->list);
> cwq = init_cpu_workqueue(wq, singlethread_cpu);
> err = create_workqueue_thread(cwq, singlethread_cpu);
> + if (!err)
> + wake_up_process(cwq->thread);
> } else {
> - mutex_lock(&workqueue_mutex);
> + spin_lock(&workqueue_lock);
> list_add(&wq->list, &workqueues);
> -
> - for_each_possible_cpu(cpu) {
> + spin_unlock(&workqueue_lock);
> + for_each_online_cpu(cpu) {
> cwq = init_cpu_workqueue(wq, cpu);
> - if (err || !(cpu_online(cpu) || cpu == embryonic_cpu))
> - continue;
> err = create_workqueue_thread(cwq, cpu);
> + if (err)
> + break;
No, we can't break. We are going to execute destroy_workqueue(), it will
iterate over all cwqs.
> +static void take_over_work(struct workqueue_struct *wq, unsigned int cpu)
> +{
> + struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
> + struct list_head list;
> + struct work_struct *work;
> +
> + spin_lock_irq(&cwq->lock);
> + list_replace_init(&cwq->worklist, &list);
> +
> + while (!list_empty(&list)) {
> + work = list_entry(list.next,struct work_struct,entry);
> + list_del(&work->entry);
> + __queue_work(per_cpu_ptr(wq->cpu_wq, smp_processor_id()), work);
> + }
> +
> + spin_unlock_irq(&cwq->lock);
> +}
I think this is unneeded complication, but ok, should work.
> static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
> unsigned long action,
> void *hcpu)
> + case CPU_UP_CANCELED:
> + list_for_each_entry(wq, &workqueues, list) {
> + if (!per_cpu_ptr(wq->cpu_wq, hotcpu)->thread)
> + continue;
> + /* Unbind so it can run. */
> + kthread_bind(per_cpu_ptr(wq->cpu_wq, hotcpu)->thread,
> + any_online_cpu(cpu_online_map));
> + cleanup_workqueue_thread(wq, hotcpu);
> }
> + break;
> +
> + case CPU_DEAD:
> + list_for_each_entry(wq, &workqueues, list)
> + take_over_work(wq, hotcpu);
> + break;
> +
> + case CPU_DEAD_KILL_THREADS:
> + list_for_each_entry(wq, &workqueues, list)
> + cleanup_workqueue_thread(wq, hotcpu);
> }
Both CPU_UP_CANCELED and CPU_DEAD_KILL_THREADS runs after thaw_processes(),
this means that workqueue_cpu_callback() is racy wrt create/destroy workqueue,
we should take the mutex, and it can't be spinlock_t.
Oleg.
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