sched: enable early use of sched_clock()

some platforms have sched_clock() implementations that cannot be called
very early during wakeup. If it's called it might hang or crash in hard
to debug ways. So only call update_rq_clock() [which calls sched_clock()]
if sched_init() has already been called. (rq->idle is NULL before the
scheduler is initialized.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 1 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 67d9d1799d86..c6e551de795b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -488,7 +488,12 @@ unsigned long long cpu_clock(int cpu)
 
         local_irq_save(flags);
         rq = cpu_rq(cpu);
-        update_rq_clock(rq);
+        /*
+         * 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);
         now = rq->clock;
         local_irq_restore(flags);