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>

1 files changed, 10 insertions, 4 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index b387a8de26a5..7286ccb01082 100644
--- 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