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 :)

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1391803122-4425-2-git-send-email-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 49db434a35d05dac966828190a80bec6b64aa954..06da865043ecbebe4c0280349dd18924a40e0d5c 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4443,6 +4443,7 @@ 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