sched: make early bootup sched_clock() use safer

do not call sched_clock() too early. Not only might rq->idle
not be set up - but pure per-cpu data might not be accessible
either.

this solves an ia64 early bootup hang with CONFIG_PRINTK_TIME=y.

Tested-by: Tony Luck <tony.luck@gmail.com>
Acked-by: Tony Luck <tony.luck@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index b387a8de26a5f9ca8b6e2e9d3ad33f66fbf65882..7286ccb01082e62b8b73c145d68d904a41338ad3 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -668,6 +668,8 @@ const_debug unsigned int sysctl_sched_nr_migrate = 32;
  */
 unsigned int sysctl_sched_rt_period = 1000000;
 
+static __read_mostly int scheduler_running;
+
 /*
  * part of the period that we allow rt tasks to run in us.
  * default: 0.95s
@@ -689,14 +691,16 @@ unsigned long long cpu_clock(int cpu)
        unsigned long flags;
        struct rq *rq;
 
-       local_irq_save(flags);
-       rq = cpu_rq(cpu);
        /*
         * Only call sched_clock() if the scheduler has already been
         * initialized (some code might call cpu_clock() very early):
         */
-       if (rq->idle)
-               update_rq_clock(rq);
+       if (unlikely(!scheduler_running))
+               return 0;
+
+       local_irq_save(flags);
+       rq = cpu_rq(cpu);
+       update_rq_clock(rq);
        now = rq->clock;
        local_irq_restore(flags);
 
@@ -7284,6 +7288,8 @@ void __init sched_init(void)
         * During early bootup we pretend to be a normal task:
         */
        current->sched_class = &fair_sched_class;
+
+       scheduler_running = 1;
 }
 
 #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP