diff options
authorThomas Gleixner <tglx@linutronix.de>2007-09-16 15:36:43 +0200
committerThomas Gleixner <tglx@chaos.(none)>2007-09-16 15:36:43 +0200
commit5e41d0d60a534d2a5dc9772600a58f44c8d12506 (patch)
parent31d9b3938c0459e5e9755ce0a98ac1e24eeff972 (diff)
clockevents: prevent stale tick update on offline cpu
Taking a cpu offline removes the cpu from the online mask before the CPU_DEAD notification is done. The clock events layer does the cleanup of the dead CPU from the CPU_DEAD notifier chain. tick_do_timer_cpu is used to avoid xtime lock contention by assigning the task of jiffies xtime updates to one CPU. If a CPU is taken offline, then this assignment becomes stale. This went unnoticed because most of the time the offline CPU went dead before the online CPU reached __cpu_die(), where the CPU_DEAD state is checked. In the case that the offline CPU did not reach the DEAD state before we reach __cpu_die(), the code in there goes to sleep for 100ms. Due to the stale time update assignment, the system is stuck forever. Take the assignment away when a cpu is not longer in the cpu_online_mask. We do this in the last call to tick_nohz_stop_sched_tick() when the offline CPU is on the way to the final play_dead() idle entry. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
1 files changed, 12 insertions, 0 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b416995b975..8c3fef1db09 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -160,6 +160,18 @@ void tick_nohz_stop_sched_tick(void)
cpu = smp_processor_id();
ts = &per_cpu(tick_cpu_sched, cpu);
+ /*
+ * If this cpu is offline and it is the one which updates
+ * jiffies, then give up the assignment and let it be taken by
+ * the cpu which runs the tick timer next. If we don't drop
+ * this here the jiffies might be stale and do_timer() never
+ * invoked.
+ */
+ if (unlikely(!cpu_online(cpu))) {
+ if (cpu == tick_do_timer_cpu)
+ tick_do_timer_cpu = -1;
+ }
if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
goto end;