Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [RFC PATCH v2 1/2] workqueue: Unbind workers before sending them to exit() | Date | Thu, 28 Jul 2022 11:54:19 +0100 |
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On 28/07/22 01:13, Lai Jiangshan wrote: > Quick review before going to sleep. >
Thanks!
> On Wed, Jul 27, 2022 at 7:54 PM Valentin Schneider <vschneid@redhat.com> wrote: >> @@ -1806,8 +1806,10 @@ static void worker_enter_idle(struct worker *worker) >> /* idle_list is LIFO */ >> list_add(&worker->entry, &pool->idle_list); >> >> - if (too_many_workers(pool) && !timer_pending(&pool->idle_timer)) >> - mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT); >> + if (too_many_workers(pool) && !delayed_work_pending(&pool->idle_reaper_work)) >> + mod_delayed_work(system_unbound_wq, >> + &pool->idle_reaper_work, >> + IDLE_WORKER_TIMEOUT); > > system_unbound_wq doesn't have a rescuer. > > A new workqueue with a rescuer needs to be created and used for > this purpose. >
Right, I think it makes sense for those work items to be attached to a WQ_MEM_RECLAIM workqueue. Should I add that as a workqueue-internal thing?
>> >> /* Sanity check nr_running. */ >> WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running); >> @@ -1972,9 +1974,29 @@ static struct worker *create_worker(struct worker_pool *pool) >> return NULL; >> } >> >> +static void unbind_worker(struct worker *worker) >> +{ >> + kthread_set_per_cpu(worker->task, -1); >> + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0); >> +} >> + >> +static void rebind_worker(struct worker *worker, struct worker_pool *pool) >> +{ >> + kthread_set_per_cpu(worker->task, pool->cpu); >> + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask) < 0); >> +} >> + >> +static void reap_worker(struct worker *worker) >> +{ >> + list_del_init(&worker->entry); >> + unbind_worker(worker); >> + wake_up_process(worker->task); > > > Since WORKER_DIE is set, the worker can be possible freed now > if there is another source to wake it up. >
My understanding for having reap_worker() be "safe" to use outside of raw_spin_lock_irq(pool->lock) is that pool->idle_list is never accessed outside of the pool->lock, and wake_up_worker() only wakes a worker that is in that list. So with destroy_worker() detaching the worker from pool->idle_list under pool->lock, I'm not aware of a codepath other than reap_worker() that could wake it up.
The only wake_up_process() I see that doesn't involve the pool->idle_list is in send_mayday(), but AFAIA rescuers can never end up in the idle_list and are specifically destroyed in destroy_workqueue().
> I think reverting a part of the commit 60f5a4bcf852("workqueue: > async worker destruction") to make use of kthread_stop() > in destroy_worker() should be a good idea.
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