Re: [PATCH 1/1] sched/core: Fix stuck on completion for affine_move_task() when stopper disable

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Sep 27, 2023 at 03:57:35PM +0000, Kuyo Chang (張建文) wrote:

> This issue occurs at CPU hotplug/set_affinity stress test.
> The reproduce ratio is very low(about once a week).

I'm assuming you're running an arm64 kernel with preempt_full=y (the
default for arm64).

Could you please test the below?

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d8fd29d66b24..079a63b8a954 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2645,9 +2645,11 @@ static int migration_cpu_stop(void *data)
 		 * it.
 		 */
 		WARN_ON_ONCE(!pending->stop_pending);
+		preempt_disable();
 		task_rq_unlock(rq, p, &rf);
 		stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
 				    &pending->arg, &pending->stop_work);
+		preempt_enable();
 		return 0;
 	}
 out:
@@ -2967,12 +2969,13 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
 			complete = true;
 		}
 
+		preempt_disable();
 		task_rq_unlock(rq, p, rf);
-
 		if (push_task) {
 			stop_one_cpu_nowait(rq->cpu, push_cpu_stop,
 					    p, &rq->push_work);
 		}
+		preempt_enable();
 
 		if (complete)
 			complete_all(&pending->done);
@@ -3038,12 +3041,13 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
 		if (flags & SCA_MIGRATE_ENABLE)
 			p->migration_flags &= ~MDF_PUSH;
 
+		preempt_disable();
 		task_rq_unlock(rq, p, rf);
-
 		if (!stop_pending) {
 			stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,
 					    &pending->arg, &pending->stop_work);
 		}
+		preempt_enable();
 
 		if (flags & SCA_MIGRATE_ENABLE)
 			return 0;
@@ -9459,6 +9461,7 @@ static void balance_push(struct rq *rq)
 	 * Temporarily drop rq->lock such that we can wake-up the stop task.
 	 * Both preemption and IRQs are still disabled.
 	 */
+	preempt_disable();
 	raw_spin_rq_unlock(rq);
 	stop_one_cpu_nowait(rq->cpu, __balance_push_cpu_stop, push_task,
 			    this_cpu_ptr(&push_work));
@@ -9468,6 +9471,7 @@ static void balance_push(struct rq *rq)
 	 * which kthread_is_per_cpu() and will push this task away.
 	 */
 	raw_spin_rq_lock(rq);
+	preempt_enable();
 }
 
 static void balance_push_set(int cpu, bool on)