sched: fix sched_clock_cpu()

Make sched_clock_cpu() return 0 before it has been initialized and avoid
corrupting its state due to doing so.

This fixes the weird printk timestamp jump reported.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

1 files changed, 14 insertions, 4 deletions

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 9c597e37f7de..ce05271219ab 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -59,22 +59,26 @@ static inline struct sched_clock_data *cpu_sdc(int cpu)
         return &per_cpu(sched_clock_data, cpu);
 }
 
+static __read_mostly int sched_clock_running;
+
 void sched_clock_init(void)
 {
         u64 ktime_now = ktime_to_ns(ktime_get());
-        u64 now = 0;
+        unsigned long now_jiffies = jiffies;
         int cpu;
 
         for_each_possible_cpu(cpu) {
                 struct sched_clock_data *scd = cpu_sdc(cpu);
 
                 scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
-                scd->prev_jiffies = jiffies;
-                scd->prev_raw = now;
-                scd->tick_raw = now;
+                scd->prev_jiffies = now_jiffies;
+                scd->prev_raw = 0;
+                scd->tick_raw = 0;
                 scd->tick_gtod = ktime_now;
                 scd->clock = ktime_now;
         }
+
+        sched_clock_running = 1;
 }
 
 /*
@@ -136,6 +140,9 @@ u64 sched_clock_cpu(int cpu)
         struct sched_clock_data *scd = cpu_sdc(cpu);
         u64 now, clock;
 
+        if (unlikely(!sched_clock_running))
+                return 0ull;
+
         WARN_ON_ONCE(!irqs_disabled());
         now = sched_clock();
 
@@ -174,6 +181,9 @@ void sched_clock_tick(void)
         struct sched_clock_data *scd = this_scd();
         u64 now, now_gtod;
 
+        if (unlikely(!sched_clock_running))
+                return;
+
         WARN_ON_ONCE(!irqs_disabled());
 
         now = sched_clock();