Re: BUG: HANG_DETECT waiting for migration_cpu_stop() complete

[Hillf Danton <hdanton@sina.com>]

On 5 Sep 2022 10:47:36 +0800 Jing-Ting Wu <jing-ting.wu@mediatek.com> wrote
> 
> We meet the HANG_DETECT happened in T SW version with kernel-5.15.
> Many tasks have been blocked for a long time.
> 
> Root cause:
> migration_cpu_stop() is not complete due to is_migration_disabled(p) is
> true, complete is false and complete_all() never get executed.
> It let other task wait the rwsem.

See if handing task over to stopper again in case of migration disabled
could survive your tests.

Hillf

--- linux-5.15/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2322,9 +2322,7 @@ static int migration_cpu_stop(void *data
 	 * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
 	 * we're holding p->pi_lock.
 	 */
-	if (task_rq(p) == rq) {
-		if (is_migration_disabled(p))
-			goto out;
+	if (task_rq(p) == rq && !is_migration_disabled(p)) {
 
 		if (pending) {
 			p->migration_pending = NULL;