linux-kernel - [tip:sched/core] sched: Init idle->on_rq in init

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Date:	Fri, 21 Feb 2014 13:31:28 -0800
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	mingo@...nel.org, peterz@...radead.org, bigeasy@...utronix.de,
	tglx@...utronix.de
Subject: [tip:sched/core] sched: Init idle->on_rq in init_idle()

Commit-ID:  e037fef5fb7d2c887916576c1a288c821b6268f4
Gitweb:     http://git.kernel.org/tip/e037fef5fb7d2c887916576c1a288c821b6268f4
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Fri, 7 Feb 2014 20:58:37 +0100
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 21 Feb 2014 21:43:18 +0100

sched: Init idle->on_rq in init_idle()

We stumbled in RT over a SMP bringup issue on ARM where the
idle->on_rq == 0 was causing try_to_wakeup() on the other cpu to run
into nada land.

After adding that idle->on_rq = 1; I was able to find the root cause
of the lockup: the idle task on the newly woken up cpu was fiddling
with a sleeping spinlock, which is a nono.

I kept the init of idle->on_rq to keep the state consistent and to
avoid another long lasting debug session.

As a side note, the whole debug mess could have been avoided if
might_sleep() would have yelled when called from the idle task. That's
fixed with patch 2/6 - and that one actually has a changelog :)

Cc: Ingo Molnar <mingo@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/1391803122-4425-2-git-send-email-bigeasy@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4c8aaf0..86e0558 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4451,6 +4451,7 @@ void init_idle(struct task_struct *idle, int cpu)
 	rcu_read_unlock();
 
 	rq->curr = rq->idle = idle;
+	idle->on_rq = 1;
 #if defined(CONFIG_SMP)
 	idle->on_cpu = 1;
 #endif
--
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