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From: Peter Zijlstra <peterz@infradead.org>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>, Qian Cai <cai@redhat.com>,
	Vincent Donnefort <vincent.donnefort@arm.com>,
	Dexuan Cui <decui@microsoft.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU
Date: Sat, 16 Jan 2021 19:46:47 +0100	[thread overview]
Message-ID: <YAM0l2WItxyaHr2N@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAJhGHyBKexR+UmR2Hzf-OU9_9zfc0V6r=s2rS=N8sc+2VnN3mw@mail.gmail.com>

On Sun, Jan 17, 2021 at 12:14:34AM +0800, Lai Jiangshan wrote:

> BP:                 AP:                  worker:
> cpus_write_lock()
> bringup_cpu()                            work_item_func()
>   bringup_wait_for_ap                      get_online_cpus()
>                     kthread_park(worker)

Thanks, pictures are easier. Agreed, that a problem.

I've also found another problem I think.  rescuer_thread becomes part of
for_each_pool_worker() between worker_attach_to_pool() and
worker_detach_from_pool(), so it would try and do kthread_park() on
rescuer, when things align. And rescuer_thread() doesn't have a
kthread_parkme().

And we already rely on this 'ugly' thing of first doing
kthread_set_per_cpu() and fixing up the affinity later for the rescuer.

Let me restart the SRCU-P testing with the below delta applied.

---
 kernel/workqueue.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1db769b116a1..894bb885b40b 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2368,7 +2368,6 @@ static int worker_thread(void *__worker)
 	/* tell the scheduler that this is a workqueue worker */
 	set_pf_worker(true);
 woke_up:
-	kthread_parkme();
 	raw_spin_lock_irq(&pool->lock);
 
 	/* am I supposed to die? */
@@ -2426,7 +2425,7 @@ static int worker_thread(void *__worker)
 			move_linked_works(work, &worker->scheduled, NULL);
 			process_scheduled_works(worker);
 		}
-	} while (keep_working(pool) && !kthread_should_park());
+	} while (keep_working(pool));
 
 	worker_set_flags(worker, WORKER_PREP);
 sleep:
@@ -2438,12 +2437,9 @@ static int worker_thread(void *__worker)
 	 * event.
 	 */
 	worker_enter_idle(worker);
-	set_current_state(TASK_IDLE);
+	__set_current_state(TASK_IDLE);
 	raw_spin_unlock_irq(&pool->lock);
-
-	if (!kthread_should_park())
-		schedule();
-
+	schedule();
 	goto woke_up;
 }
 
@@ -4979,9 +4975,9 @@ static void rebind_workers(struct worker_pool *pool)
 	 * from CPU_ONLINE, the following shouldn't fail.
 	 */
 	for_each_pool_worker(worker, pool) {
-		WARN_ON_ONCE(kthread_park(worker->task) < 0);
 		kthread_set_per_cpu(worker->task, pool->cpu);
-		kthread_unpark(worker->task);
+		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
+						  pool->attrs->cpumask) < 0);
 	}
 
 	raw_spin_lock_irq(&pool->lock);

  reply	other threads:[~2021-01-16 18:49 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-12 14:43 [PATCH 0/4] sched: Fix hot-unplug regressions Peter Zijlstra
2021-01-12 14:43 ` [PATCH 2/4] kthread: Extract KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-12 14:43 ` [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-12 16:36   ` Lai Jiangshan
2021-01-13 11:43     ` Peter Zijlstra
2021-01-12 17:57   ` Valentin Schneider
2021-01-13 13:28   ` Lai Jiangshan
2021-01-13 14:16     ` Valentin Schneider
2021-01-13 17:52       ` Paul E. McKenney
2021-01-13 18:43         ` Valentin Schneider
2021-01-13 18:59           ` Paul E. McKenney
2021-01-14 13:12     ` Peter Zijlstra
2021-01-14 13:21       ` Valentin Schneider
2021-01-14 15:34         ` Peter Zijlstra
2021-01-16  6:27           ` Lai Jiangshan
2021-01-16 12:45             ` Peter Zijlstra
2021-01-16 14:45               ` Lai Jiangshan
2021-01-16 15:16                 ` Peter Zijlstra
2021-01-16 16:14                   ` Lai Jiangshan
2021-01-16 18:46                     ` Peter Zijlstra [this message]
2021-01-17  9:54                       ` Peter Zijlstra
2021-01-16 15:13               ` Peter Zijlstra
2021-01-12 14:43 ` [PATCH 4/4] sched: Fix CPU hotplug / tighten is_per_cpu_kthread() Peter Zijlstra

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