linux-kernel - Re: WARNING at kernel/sched/core.c:2013 migration_cpu

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Date:   Mon, 16 Nov 2020 10:00:14 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org
Subject: Re: WARNING at kernel/sched/core.c:2013 migration_cpu_stop+0x2e3/0x330


On 15/11/20 22:32, Oleksandr Natalenko wrote:
> Hi.
>
> I'm running v5.10-rc3-rt7 for some time, and I came across this splat in 
> dmesg:
>
> ```
> [118769.951010] ------------[ cut here ]------------
> [118769.951013] WARNING: CPU: 19 PID: 146 at kernel/sched/core.c:2013 

Err, I didn't pick up on this back then, but isn't that check bogus? If the
task is enqueued elsewhere, it's valid for it not to be affined
'here'. Also that is_migration_disabled() check within is_cpu_allowed()
makes me think this isn't the best thing to call on a remote task.

---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1218f3ce1713..47d5b677585f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2010,7 +2010,7 @@ static int migration_cpu_stop(void *data)
 		 * valid again. Nothing to do.
 		 */
 		if (!pending) {
-			WARN_ON_ONCE(!is_cpu_allowed(p, cpu_of(rq)));
+			WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), p->cpus_ptr));
 			goto out;
 		}