linux-kernel - Re: [tip:sched/core] sched: Change the sched_class::set_cpus

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Date:	Thu, 13 Aug 2015 22:37:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	hpa@...or.com, torvalds@...ux-foundation.org, efault@....de,
	tglx@...utronix.de, linux-kernel@...r.kernel.org, mingo@...nel.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched: Change the
 sched_class::set_cpus_allowed( ) calling context

On Thu, Aug 13, 2015 at 02:47:20PM -0400, Sasha Levin wrote:
> [79817.224383] bad: scheduling from the idle thread!
> [79817.224900] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc6-next-20150813-sasha-00040-g059fd6d #2431
> [79817.225709]  ffffffffae0c6320 ffff880051b77c00 ffffffffade7f739 ffff8800a69e15c0
> [79817.226419]  ffff880051b77c18 ffffffffa43c4ed3 ffff880051be8000 ffff880051b77c48
> [79817.227122]  ffffffffa43a7ffb ffff880051be8000 ffff8800a69e15c0 ffffffffae094d40
> [79817.227806] Call Trace:
> [79817.228039] dump_stack (lib/dump_stack.c:52)
> [79817.228503] dequeue_task_idle (kernel/sched/idle_task.c:45)
> [79817.229005] dequeue_task (kernel/sched/core.c:839)
> [79817.229485] do_set_cpus_allowed (kernel/sched/core.c:1178 (discriminator 9))
> [79817.230006] init_idle (kernel/sched/core.c:4937)
> [79817.230467] idle_thread_get (kernel/smpboot.c:35)

Dhurr.. so oddly enough my actual hardware boots without issue.

But I can see how that could go wrong, does the below make your
(virtual) machine happy again?

---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 56aed8fce3cb..2d2871e2cf5d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4924,7 +4924,7 @@ void init_idle(struct task_struct *idle, int cpu)
 	idle->state = TASK_RUNNING;
 	idle->se.exec_start = sched_clock();
 
-	do_set_cpus_allowed(idle, cpumask_of(cpu));
+	set_cpus_allowed_common(idle, cpumask_of(cpu));
 	/*
 	 * We're having a chicken and egg problem, even though we are
 	 * holding rq->lock, the cpu isn't yet set to this cpu so the
--
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