sched: fix init_idle()'s use of sched_clock()

Maciej Rutecki reported:

> I have this bug during suspend to disk:
>
> [  188.592151] Enabling non-boot CPUs ...
> [  188.592151] SMP alternatives: switching to SMP code
> [  188.666058] BUG: using smp_processor_id() in preemptible
> [00000000]
> code: suspend_to_disk/2934
> [  188.666064] caller is native_sched_clock+0x2b/0x80

Which, as noted by Linus, was caused by me, via:

  7cbaef9c "sched: optimize sched_clock() a bit"

Move the rq locking a bit earlier in the initialization sequence,
that will make the sched_clock() call in init_idle() non-preemptible.

Reported-by: Maciej Rutecki <maciej.rutecki@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 3bafbe350f4f..c94baf2969e7 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5870,6 +5870,8 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
         struct rq *rq = cpu_rq(cpu);
         unsigned long flags;
 
+        spin_lock_irqsave(&rq->lock, flags);
+
         __sched_fork(idle);
         idle->se.exec_start = sched_clock();
 
@@ -5877,7 +5879,6 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
         idle->cpus_allowed = cpumask_of_cpu(cpu);
         __set_task_cpu(idle, cpu);
 
-        spin_lock_irqsave(&rq->lock, flags);
         rq->curr = rq->idle = idle;
 #if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)
         idle->oncpu = 1;